EPA/600/R-07/086F | September 2012 | www.epa.gov
United States
Environmental Protection
Agency
Climate and Land-Use Change Effects
on Ecological Resources in Three Watersheds:
A Synthesis Report
National Center for Environmental Assessment
Office of Research and Development
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EPA/600/R-07/086F
September 2012
Climate and Land-Use Change Effects on Ecological
Resources in Three Watersheds:
A Synthesis Report
Global Change Research Program
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Washington, DC 20460
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DISCLAIMER
This document has been reviewed in accordance with U.S. Environmental Protection
Agency policy and approved for publication. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use.
ABSTRACT
During the early 2000s, the Environmental Protection Agency's (EPA's) Office of
Research and Development, Global Change Research Program, supported three watershed
assessments to evaluate different approaches and tools for understanding and managing climate
and land-use change impacts on watershed ecological resources. Watershed assessments were
conducted for (1) several small rivers in southern Maryland, (2) Arizona's San Pedro River, and
(3) California's Sacramento River. In this report, we comparatively analyze the three case-study
approaches in order to develop recommendations that may be useful as guidance to others
conducting similar assessments. Key insights gained from these studies include:
1. Prioritize locations for studies to maximize decision support.
2. Target selection of stakeholders, establish credibility of underlying methods and
models, and incorporate incentives for mutually beneficial results.
3. Provide essential climate science capabilities and tools to project teams.
4. Develop model linkages at the onset, carry out assessment activities at multiple
scales, and require explicit uncertainty analysis of results.
The watershed assessment case studies described in this report yield richness of detail in
terms of methods and results, as well as inform more generally on best practices for conducting
future watershed assessments. However these were pioneering studies addressing difficult and
complex problems. Future assessments will continue to refine the understanding of how to
maximize decision support, including providing necessary keystone capabilities and tools to
effectively estimate climate change vulnerabilities, developing and supporting successful
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stakeholder processes, and characterizing uncertainty and scaling or transferring results to
increase their relevance.
Cover Photos:
Cover photo of the Sacramento River, courtesy of William L. Graf, University of South Carolina.
Cover photo of the San Pedro River, courtesy of Vladimir Steblina.
Cover Photo of Patapsco River in the spring, courtesy of the Chesapeake Bay Program (www.chesapeakebay.netX
Preferred citation:
U.S. EPA (Environmental Protection Agency). (2012) Climate and land-use change effects on ecological resources
in three watersheds: a synthesis report. National Center for Environmental Assessment, Washington, DC;
EPA/600/R-07/086F. Available from the National Technical Information Service, Springfield, VA, and online at
http ://www. epa. gov/ncea.
in
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CONTENTS
LIST OF TABLES vi
LIST OF FIGURES vi
LIST OF ABBREVIATIONS AND ACRONYMS vii
AUTHORS, CONTRIBUTORS, AND REVIEWERS viii
EXECUTIVE SUMMARY x
1. INTRODUCTION 1
1.1. Purpose of the Report 1
1.2. The Case Studies 3
1.2.1. Motivation for the Watershed Case Studies 3
1.2.2. Criteria for Selecting Case Studies 5
1.2.3. The Portfolio of Case Studies 5
2. CASE-STUDY RESULTS 10
2. I.Maryland 10
2.1.1. Goals of the Case-Study Assessment 10
2.1.2. Major Stressors 11
2.1.3. Assessment Methods 12
2.1.3.1. Submodels 12
2.1.3.2. Land-Use and Climate Change Scenarios 15
2.1.4. Impacts and Findings 15
2.1.5. Methods and Results Applicable to Other Watersheds 17
2.2. San Pedro 17
2.2.1. Goals of the Case-Study Assessment 19
2.2.2. Major Stressors 19
2.2.3. Assessment Methods 20
2.2.3.1. Climate Change Scenarios 20
2.2.3.2. Simulation of Riparian Vegetation Dynamics 22
2.2.3.3. Changes in Avian Biodiversity Resulting from Vegetation
Changes 24
2.2.4. Impacts and Findings 25
2.2.5. Methods and Results Applicable to Other Watersheds 26
2.3. Sacramento 27
2.3.1. Goals of the Case-Study Assessment 27
2.3.2. Major Stressors 27
2.3.3. Assessment Methods 30
2.3.4. Impacts and Findings 32
2.3.5. Methods and Results Applicable to Other Watersheds 34
3. FINDINGS AND RECOMMENDATIONS 35
3.1. Assessment Processes and Results 35
3.1.1. Case-study Team Composition and Management 36
3.1.1.1. Findings 36
3.1.1.2. Recommendation #1—Provide Keystone Capabilities and
Tools to Project Teams 37
3.1.2. Research Design, Case-Study Results, and Future Applicability 38
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3.1.2.1. Findings (Research Design) 38
3.1.2.2. Findings (Case-Study Results) 39
3.1.2.3. Findings (Future Applications) 41
3.1.2.4. Recommendation #2—Emphasize Model Linkages 42
3.1.3. Complexity of Varying Spatial Scales in Watershed Assessments 43
3.1.3.1. Findings 43
3.1.3.2. Recommendation #3—Carry Out Assessment Activities at
Multiple Scales 44
3.1.4. Estimation and Communication of Uncertainty 45
3.1.4.1. Findings (Type and Extent of Uncertainties) 45
3.1.4.2. Findings (Methods for Estimating and Communicating
Uncertainty) 46
3.1.4.3. Recommendation #4—Require Explicit Uncertainty
Analyses as Part of any Assessment 47
3.2. Stakeholder Processes 48
3.2.1. Defining and Identifying Appropriate Stakeholders 49
3.2.1.1. Findings 49
3.2.1.2. Recommendation #5—Build on Existing Stakeholder
Relationships, Target Selection, and Establish Credibility 50
3.2.2. Maintaining Stakeholder Processes 51
3.2.2.1. Findings 51
3.2.2.2. Recommendation #6—Incorporate Incentives for Mutually
Beneficial Results 52
3.3. Relevance of Impacts to Decision Making 54
3.3.1.1. Recommendation #7—Design Selection Criteria to
Maximize Decision Support 55
4. CONCLUSIONS 57
5. REFERENCES 59
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LIST OF TABLES
1. Comparison of the three watersheds 7
2. Comparison of Maryland baseline and climate change scenarios. Climate change driver series
used in the Forecasted Indices for Fish (FIF) for baseline and future climate scenarios 13
3. Summary of Maryland's 10 land-use and climate change scenarios used to project impacts on
stream fish assemblages 16
4. Summary of recommendations for future watershed assessments 35
LIST OF FIGURES
1. Geographic locations of case studies across the United States....
2. Study site locations (watersheds outlined with specific sites indicated by black dots), gauging
site, and weather station. Within the watershed boundaries, dark grey represents urban land,
light grey represents agricultural land, and white represents forested land 11
3. Map of the Upper San Pedro River riparian ecosystem 18
4. Map of the San Francisco Bay Delta Watershed, which includes the Sacramento River
Watershed 28
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LIST OF ABBREVIATIONS AND ACRONYMS
A2
B2
BLM
EPA
FIF
GCM
GCRP
HadCMS
HSI
NCEA
ORD
PCM
SAHRA
SI
SPRNCA
SWAT
USFWS
USPP
WEAP
medium-high
medium-low
Bureau of Land Management
Environmental Protection Agency
forecasted indices for fish
General Circulation Model
Global Change Research Program
Hadley Centre Model v3
Habitat Suitability Index
National Center for Environmental Assessment
Office of Research and Development
Parallel Climate Model
semi-arid hydrology and riparian areas
suitability index
San Pedro Riparian National Conservation Area
Soil Water Assessment Tool
U.S. Fish and Wildlife Service
Upper San Pedro Partnership
Water Evaluation and Planning
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
AUTHORS
Susan H. Julius, U.S. EPA ORD/NCEA
Thomas E. Johnson, U.S. EPA ORD/NCEA
Britta G. Bierwagen, U.S. EPA ORD/NCEA
Susan Asam, ICF International, Inc.
Elizabeth Strange, ICF International, Inc.
Randall Freed, ICF International, Inc.
Sarah Shapiro, ICF International, Inc.
REVIEWERS
Expert Panel
Lawrence Band, University of North Carolina at Chapel Hill
Christopher Lant, Southern Illinois University Carbondale
Marty Matlock, University of Arkansas
Kathleen Miller, National Center for Atmospheric Research
Public
James Devine, U.S. Geological Survey
Internal
Naomi Detenbeck, U.S. EPA ORD/NHEERL
Bruce Herbold, U.S. EPA Region 9
Chris Weaver, U.S. EPA ORD/NCEA
Kate Schofield, U.S. EPA ORD/NCEA
ACKNOWLEDGMENTS
The contributions of many people's experiences and insights made this report possible.
The authors would like to thank those individuals whose help was particularly valuable. First,
and most important, are those individuals who participated on the watershed case-study teams
funded by EPA. They devoted their excellent scientific and leadership skills to the conduct of
each case study and made significant methodological advances in the science of climate change
impacts. They also gave of their time and energy to reflect on ways the process of doing
assessments might be improved to produce information befitting the needs of decision makers.
These case-study teams of researchers are as follows:
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AUTHORS, CONTRIBUTORS, AND REVIEWERS (continued)
Maryland Case Study
Glenn Moglen, Principal Investigator, Virginia Technological University
Nancy Bockstael, University of Maryland
Karen Nelson, University of Maryland
Margaret Palmer, University of Maryland
James Pizzuto, University of Delaware
San Pedro Case Study
Jeff Price, Principal Investigator, World Wildlife Fund
Kate Baird, University of Arizona
Mark Dixon, Arizona State University
Hector Galbraith, Galbraith Environmental Sciences LLC
Thomas Maddock, University of Arizona
Juliet Stromberg, Arizona State University
Sacramento Case Study
Annette Huber-Lee, Principal Investigator,
Hector Galbraith, Galbraith Environmental Sciences LLC
David Purkey, Stockholm Institute of the Environment (SEI)
Jack Sieber, Stockholm Institute of the Environment (SEI)
David Yates, National Center for Atmospheric Research
We would also like to thank Catriona Rogers who contributed to the vision and direction
of the watershed assessments discussed in this report. Catriona also managed the case study
conducted by the University of Maryland.
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EXECUTIVE SUMMARY
During the early 2000s, the Environmental Protection Agency's (EPA's) Office of
Research and Development, Global Change Research Program, supported three watershed
assessments to evaluate different approaches and tools for understanding and managing climate
and land-use change impacts on watershed ecological resources. These were pioneering studies
intended not only to provide useful information in study watersheds but also to advance EPA's
general understanding of the conduct and use of impact assessments of this type to support
management decision making. Watershed assessments were conducted by three independent
case-study teams of scientists for: (1) several small rivers in southern Maryland, (2) Arizona's
San Pedro River, and (3) California's Sacramento River. Although the overarching goal of each
assessment was the same—advance our understanding of the conduct of impacts
assessments—the specific focus, scale, methods, and models of each differed based on priorities
identified by each project team. Detailed results of these studies have been published elsewhere.
In this report, we comparatively analyze the three case-study approaches in order to develop
recommendations that may be useful as guidance to others conducting similar assessments.
Specifically, each watershed assessment was evaluated to determine the following: the extent to
which results obtained in each assessment may apply to similar systems; whether the methods
used to consider the implications of climate change for ecosystem processes at the watershed
scale may be useful for other project teams and in other geographic regions of the country; and
whether the insights gained about the assessment process will be helpful to other researchers
seeking to produce useful climate impacts information for decision makers.
MARYLAND CASE STUDY
The specific goal of the Maryland case study was to better understand how the effects of
climate variability and change on stream ecosystems depend on land-use choices in surrounding
areas. The interaction of climate and land-use change is important in the context of regional
planning and adaptation to climate change. The Maryland case-study team developed and
applied a model, the Forecasted Indices for Fish (FIF), to assess the combined effects of land-use
change and climate change on stream fish assemblages over the next century. The scenarios of
future change used in their analyses were the following: (1) baseline scenario (low urbanization;
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no new construction; and present-day climate), (2) baseline scenario with urbanization (higher
impervious surface, lower forest cover, significant construction activity), (3) four future climate
change scenarios—based on projections from the Hadley CMS and Parallel Climate Models
(PCM) under medium-high (A2) and medium-low (B2) emissions scenarios, and (4) the same
four climate change scenarios plus urbanization.
Four pathways were examined by which urbanization and climate change are likely to
directly and indirectly affect fish reproduction and growth—spawning temperatures, spawning
substrate, juvenile growth, and adult growth. Modeling results showed that urbanization alone
affected growth or reproduction only slightly, suppressing these functions in 8 of 39 fish species.
However, climate change alone depressed these functions in 22-29 species. The combination of
both stressors usually increased the number of stressed species, sometimes to a considerable
degree. Under all of these scenarios, substantial changes in fish assemblage composition are
anticipated, including loss of diversity.
Urban growth and its interaction with climate change could dramatically affect ecosystem
structure and services through impacts to headwater streams. While mitigating the causes of
climate change itself may not be addressed at the local scale to a significant degree, the
Maryland case-study team concluded that stream impacts may be reduced through decisions
made about how land uses change in the future.
Models and results could be applied to other Piedmont streams for hydrologic changes,
and other watersheds of the U.S. East Coast with similar species mixes for the fish assemblage
results (using models reparameterized with local data). For streams with different fish
assemblages, it might be possible to develop a similar model if local data are available on food
resources and on the recruitment, growth, and survival of the species of interest.
SAN PEDRO CASE STUDY
The goal of the San Pedro case study was to determine the likely coupled effects of
climate change, urbanization, and groundwater withdrawals on ecological resources and
biodiversity in the San Pedro Riparian National Conservation Area. This information is
important to aid in managing development and hydrologic conditions in this area.
Five future climate change scenarios were evaluated: (1) baseline (no climate change),
(2) warmer (progressive temperature warming over 100 years, with a 4°C increase in maximum
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daily temperature and a 6°C increase in minimum daily temperature by 2102), (3) warmer and
dryer (same progressive temperature warming as the warm scenario and a progressive decline in
winter daily precipitation of 50% by 2102), (4) warmer and wetter (same progressive
temperature warming as the warm scenario with a progressive increase in winter daily
precipitation of 50% by 2102), and (5) warmer and very wet (same progressive temperature
warming as the warm scenario with a progressive increase in winter daily precipitation of 100%
by 2102).
The San Pedro case-study team analyzed species, vegetation, and habitat suitability first,
and then developed a model linking vegetation, groundwater, and surface water to tie the
fluctuations in groundwater levels to evapotranspiration. Simulations using this model showed
that altered hydrology resulting from climate change would fragment existing riparian and
wetland communities and lead to their replacement by more mesic or xeric communities (i.e.,
vegetation more typical of the desert matrix). The influence of climate change on pioneer
riparian communities depended on the magnitude and direction of precipitation changes: less
winter precipitation would result in fewer winter floods, lower rates of channel migration, and
much lower cottonwood and willow recruitment rates; increased winter precipitation would
result in larger and more frequent winter floods, higher channel migration rates, and higher
cottonwood and willow recruitment rates.
The San Pedro case-study team also determined that avian biodiversity would be affected
by climate change, with some of the most abundant bird species being the most adversely
affected by changes in the vegetative community. Results from the three driest climate scenarios
suggested that the gallery forest would be fragmented or nonexistent and would result in
biodiversity loss and a likely drop in ecotourism. However, results from the warmer and wetter
scenario suggested that the water supply to the ecosystem would be adequate enough to maintain
ecosystem services and ecotourism.
Results from this case study, and, in particular, the challenges of aquifer depletion were
applicable to other areas. The vegetation, hydrology, and wildlife data inputs used in the models
made them specific to the Southwestern United States and other arid environments with
groundwater-dependent riparian systems. The channel migration model was useful in other
regions, as long as the specific vegetation data inputs were adapted; however, the approach was
not applicable to systems where vegetation uses water from the unsaturated zone.
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SACRAMENTO CASE STUDY
The focus of the Sacramento case study was to assess how global change (climate and
land-use change) would alter water supply, and how water supply and demand changes would
interact to affect offstream water uses for agriculture and instream flows for Chinook salmon
(Oncorhynchus tshawytscha) in the Sacramento Basin. The assessment was conducted using an
integrated decision support tool, the Water Evaluation and Planning (WEAP) modeling system,
to link climate and land-use/land-cover conditions with watershed conditions, water supply and
anticipated demands, ecosystem needs, infrastructure, the regulatory environment, and water
management options.
Four future climate change scenarios were evaluated based on downscaled output from
two General Circulation Models (GCMs) (PCM and Geophysical Fluid Dynamics Laboratory,
and two greenhouse gas emissions scenarios [A2 and Bl]). Two of the four scenarios resulted in
decreasing precipitation over the next century. The two remaining scenarios showed less
pronounced precipitation changes. All four scenarios projected increases in average winter and
summer temperatures over the next century ranging from a lower bound increase of 1.5°C in
winter and 1.4°C in summer to the higher bound of 3.0°C in winter and 5.0°C in summer.
All four climate change scenarios resulted in reductions in water availability, with large
impacts on supply at the end of the 100-year simulations. Reservoir levels were much lower in
the late summer and early fall, and groundwater pumping increased. The Sacramento River's
water temperature regime was altered, leading to further reductions in habitat for Chinook
salmon due to exceedances of critical spawning and rearing temperatures. Management
measures, such as improving irrigation efficiency and changing cropping patterns, resulted in a
decline in water supply requirements. Managing the releases of cold water stored in reservoirs
alleviated some of the future impacts of climate change on habitat for Chinook salmon.
The modeling framework used in this case study, WEAP, was developed specifically to
be applied in other locations. The insights gained from this case study may also be applicable in
a qualitative sense to other watersheds of similar character and nature: For example, areas where
water supply is fully subscribed among users and climatic changes will require an understanding
of the types of tradeoffs that may be required in the future—but the specific quantitative results
would not be transferable.
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FINDINGS AND RECOMMENDATIONS
The conduct and results of these three assessments suggest a number of conclusions
concerning methodological advances, lessons learned, and other insights that might be useful
guidance to others conducting similar assessments. They are provided to add to the body of
literature and general wisdom that continues to grow regarding how to conduct assessments that
provide actionable results. The following is a summary of key insights gained from these studies.
Prioritize Alternative Study Locations to Maximize Decision Support
One way to prioritize alternative study locations is to consider whether decisions are
being made in that location that are sensitive to climate change, and whether information
relevant to climate-sensitive decisions can be provided by the project team. To assess feasibility
of producing good science and sound decision support, the project team should consider the
resolution of the climate change data and the scale at which watershed-level information are
available along with the scale at which key endpoints of the decisions at hand have to be
assessed and the uncertainty introduced by bridging the gap. Assessment usefulness might also
be strengthened by building in consideration of the study design to allow extrapolation of
methods, models, or results to other locations across the country to inform broader audiences of
decision makers.
Target Selection of Stakeholders, Establish Credibility, and Incorporate Incentives for
Mutually Beneficial Results
Stakeholder engagement is an extremely important but potentially difficult and
time-consuming task. The case studies described in this report suggest that stakeholder
relationships may not need to extend to all potentially interested members of the lay public.
Rather, The best strategy may be to target only specific decision makers with a clear stake in the
study's goals. For these targeted stakeholders, project teams should consider how to demonstrate
the credibility of the science underlying their methods and models because the public debate on
climate science has been polarizing, and its relevance to issues on the ground difficult to discern
for the average person. To maintain stakeholder processes throughout the project lifetime, case-
study teams need to empower and motivate them to participate. Elements of empowerment and
motivation include ensuring transparency of the work and communicating results often,
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remaining flexible in the assessment process to incorporate feedback from stakeholders in the
analysis, recognizing and rewarding stakeholder contributions to an assessment, developing and
tracking factors to identify and institutionalize those factors that ensure and enhance stakeholder
engagement, and providing technical assistance to build capacity at the local level to refine
analyses with new information and evaluate effectiveness of adaptation responses over time.
Provide Keystone Climate Science Capabilities and Tools to Project Teams
Organizations considering supporting climate change assessments should consider
whether to provide expertise to project teams to aid in selecting, interpreting, and downscaling
GCM output (or otherwise incorporating climate change information into the assessment).
Choosing among different combinations of emission scenarios and climate sensitivities and
different methods of downscaling GCM output can be both daunting and resource intensive.
Additional tools may also be provided, such as statistical techniques to evaluate trends in climate
and hydrologic variables to complement GCM output. If climate change assessments are to be a
core task of an organization, then building capacity in keystone skills or offering tools to project
teams in areas such as climate scenario development, habitat suitability analysis, stakeholder
facilitation, and uncertainty analysis and communication should be considered.
Emphasize Model Linkages, Carry Out Assessment Activities at Multiple Scales, and
Require Explicit Uncertainty Analysis
For any climate change impact assessment, spending sufficient time in the beginning of
the design process to clearly define inputs, outputs, and interactions among submodels may help
to avoid scale-related integration issues that arise later when conducting the assessment. In the
design process, consideration should also be given to whether different spatial scales of analysis
are required to reliably address key decision endpoints when scale-dependent processes and
cross-scale effects are involved. Finally, the inclusion of explicit methods to characterize and
communicate uncertainty in the assessment design is critical to both the production of
scientifically credible results and to the appropriate use of those results in decision making.
Many techniques are available for watershed assessments that range from quantitative to
qualitative. Providing uncertainty information allows more complete consideration of the
potential range of outcomes and their implications and tradeoffs among alternative decisions.
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The watershed assessment case studies described in this report yield richness of detail in
terms of methods and results, as well as inform more generally on best practices for conducting
future watershed assessments. We hope that the results presented here will contribute to
developing a foundation for a long-term strategy for providing effective decision support. It must
be noted, however, that these were pioneering studies addressing difficult and complex
problems. As such, these studies and the lessons learned that are presented in this report
represent only a single step forward in what is sure to be an ongoing process of experimentation
and learning. Future assessments will continue to refine the understanding of how to maximize
decision support, including providing necessary keystone capabilities and tools to effectively
estimate climate change vulnerabilities, developing and supporting successful stakeholder
processes, and characterizing uncertainty and scaling or transferring results to increase their
relevance.
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1. INTRODUCTION
1.1. PURPOSE OF THE REPORT
The effects of global change drivers differ by place and in scale, necessitating
place-specific impacts information to enable stakeholders to respond appropriately. Place and
scale also determine appropriate adaptation strategies and expected outcomes. This report is a
synthesis of three watershed case-study assessments conducted by the U.S. Environmental
Protection Agency's (EPA's) Office of Research and Development (ORD), Global Change
Impacts and Adaptation Program (GCIA) to advance the capability of managers to consider
climate and land-use change in watershed management decisions. Rather than presenting
methodological details, the purpose of this synthesis report is to highlight important findings.
The watershed case studies were initiated in 2002 to better understand the effects of
global change on aquatic ecosystems within watersheds and to build capacity at appropriate
levels of decision making to respond to these effects. The studies focused on key ecosystem
services provided by the watersheds under study. Ecosystem services are the physical and
biological functions performed by natural resources and the human benefits derived from those
functions. Examples include water storage and delivery, water purification, habitat for species,
and recreational opportunities that help promote human well-being. An advantage of focusing on
ecosystem services is that they are "cross-cutting" indicators of ecological conditions that can be
readily communicated to diverse stakeholders. A focus on services also makes it possible to
concentrate a large amount of ecological data into a limited number of variables that are directly
relevant to environmental decision making.
The case studies yielded valuable scientific understanding and provided important lessons
about assessment and stakeholder processes. In this report, we set out to document those results,
findings, and lessons learned across case studies in order to inform future watershed assessments.
The remainder of Chapter 1 provides a more detailed introduction to the three watershed case
studies that were conducted. Chapter 2 describes the assessment methods used by the case-study
teams and key results, emphasizing those that are applicable elsewhere and those that support
decision making to adapt to climate change. Chapter 3 provides a discussion of the findings and
recommendations derived from those case studies, including insights gained from looking across
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all of the studies, and Chapter 4 summarizes the conclusions and implications for future
watershed assessments.
The watershed case-study assessments were conducted by three EPA-funded research
teams. National Center for Environmental Assessment (NCEA) GCIA Program provided
technical direction to each project team and contributed directly to the synthesis results presented
in this report. Additional support with this synthesis was provided by ICF International. The
locations selected for the case studies are the San Pedro River watershed led by the American
Bird Conservancy, the Sacramento River watershed led by the Tellus Institute, and watersheds in
the Washington, D.C. metropolitan area conducted by the University of Maryland. We
established criteria prior to the selection of these locations, including having a diversity of
geographic regions and river ecosystem types represented, different land-use pressures (e.g.,
agricultural pressures, urban growth pressures), different future climate-induced changes (e.g.,
increased versus decreased streamflow), and different highly valued ecosystem services. This
synthesis is based on each case-study team's scientific publications, final reports, an expert
meeting of team members held toward the end of their assessment process, and a series of
interviews conducted at the conclusion of the projects. The questions to which they responded in
the interviews are the following:
1. What are the major methodological advances developed in your case study?
2. What is the applicability of the methodologies that you employed to other watersheds? Is
applicability tied to scale, assessment endpoints, regions, or some other factor(s)?
3. What do you regard as the most important/interesting results?
4. To what extent do the case-study findings apply to other watersheds? Is applicability tied
to scale, assessment endpoints, regions, or some other factor(s)?
5. To what extent could the outputs of your project support decisions, and what types of
decisions are they? More specifically, would your results affect watershed management
practices, and if so, how? If you suspect they won't, what are the obstacles, if any?
6. To what extent did you isolate land-use change and climate change as driving factors, and
what were the results?
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7. If you were to propose additional work, what do you think the next phase of the project
should entail? What steps would be natural extensions of the work that has already been
done?
8. What do you consider to be the most important lessons learned or recommendations for
future watershed assessments?
The remainder of this chapter provides more detail on the criteria for case-study design
and selection and a brief introduction to the case studies themselves.
1.2. THE CASE STUDIES
1.2.1. Motivation for the Watershed Case Studies
The Global Change Research Act of 1990 established the U.S. Global Change Research
Program (USGCRP) to coordinate a comprehensive, multiagency research program on global
change. As a member of the USGCRP, the ORD conducts research and assessments that examine
the effect of climate, land use, and other factors on aquatic ecosystems and providing decision
support resources and adaptation options to stakeholders.
NCEA GCIA initiated watershed case studies to gain a better understanding of the effects
of global change on aquatic ecosystems and water quality, and to build capacity to respond to
these effects at appropriate levels of decision making. That led to the choice of case-study sites
that differed hydrologically and bioclimatically from each other. The studies were also in
different regions, including the Western United States, the arid/semiarid Southwest, and the
Eastern United States. We chose to focus at the watershed scale based on the knowledge that the
properties of aquatic systems are strongly influenced by the surrounding land and are often
managed and analyzed as a component of a larger watershed. The case-study approach stems
from a motivation to conduct assessments that fit into the existing watershed-based strategy used
by U.S. water management programs to integrate water management activities within
hydrologically defined drainage basins or watersheds. Additionally, NCEA GCIA has
historically had a program-wide emphasis on examining site- or region-specific impacts and
adaptation measures.
The assessment approach used for each case study integrates methods and concepts of
ecological risk assessment, ecosystem services, scenario analysis, and stakeholder engagement
processes. The design of the case studies was guided by EPA's ecological risk assessment
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framework (U.S. EPA, 1998). Climate change scenarios are used in conjunction with scenarios
of other relevant global change stressors and quantitative and conceptual models to examine the
potential impacts of global change on aquatic ecosystems. Therefore, the following list of desired
case-study design elements were identified prior to selecting the case-study sites:
• Address the combined impacts of climate change with other stressors, especially land-use
change. Over the past century, there has been a trend for a higher proportion of
precipitation to fall in intense events (e.g., more than 2 inches per event), and these
intense events contribute to nonpoint source pollution (Karl and Knight, 1998). Climate
change is anticipated to amplify this effect. Land use change (especially urbanization)
modifies stream hydrology by affecting the proportion of precipitation that immediately
enters the stream as runoff, and, thus, can also result in a "flashier" flow pattern (or
hydrograph) (Karl and Knight, 1998). The case studies were designed to examine these
(and other) interactions.
• Emphasize ecosystem services. The concept of ecosystem services enables individuals
from a cross section of society to express the values they hold for ecological processes or
functions using a common language that helps frame assessment questions relevant to
decision making. Most of the watershed management decisions address a subset of
ecosystem services that aquatic systems provide. These services—which include water
supply, hydropower, recreational amenities, habitat for species, and transportation—are
the amenities that motivate stakeholders. Thus, the case studies attempted to identify
assessment endpoints that relate to these services.
• Involve stakeholders. The goals of an assessment are to communicate insights about the
possible consequences of global change and the potential for adaptive responses.
Stakeholder involvement is crucial throughout this process to ensure that the assessment
is timely and relevant, and that results are communicated effectively.
• Use a risk assessment approach. Consistent with the human health and ecological risk
assessment programs within ORD, we applied EPA's ecological risk assessment
paradigm (U.S. EPA, 1998) to our global change assessments. The case studies were thus
designed to clearly articulate the problem and develop an analysis plan (problem
formulation), conduct an exposure assessment, effects assessment, and risk
characterization, and to use best practices to produce high-quality scientific results.
Watershed assessments employ a modification of the strict exposure-effects approach
because multiple stressors are being examined. Climate and land-use scenarios are
intended to serve as exposure scenarios in order to project a range of potential effects.
With these design elements serving as the genesis for the effort, EPA formulated the
problem that the case studies would address and selected a portfolio of three case studies.
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1.2.2. Criteria for Selecting Case Studies
The goal of the case studies was to build capacity at appropriate levels of decision
making to assess and respond to potential global change impacts on aquatic ecosystems within
watersheds. The scientifically complex environmental problems associated with global change
are beginning to be addressed under circumstances of increasingly complicated decision-making
processes. Watershed management has become a process of balancing multiple objectives, such
as drought and flood protection, habitat and species protection, and provision of adequate
supplies of water for withdrawals for municipal, industrial, and agricultural uses. Waters and
watersheds increasingly are seen as complex systems comprising both ecological and human
processes (Webler and Tuler, 1999). Undertaking a set of watershed case studies enabled us to
do an integrated examination of the processes of interest at scales that are amenable to decision
making and scientific analysis.
Criteria used to evaluate and select the three watershed case studies were the following:
• The set of sites chosen should represent different geographic scales of a watershed
system with respect to ecosystem services and stakeholders, different climate regimes,
different land-use pressures, and different vulnerabilities and intensities of use in the
context of a variety of current/existing stressors.
• Each site chosen should have services that are highly valued by the local community (and
beyond the local community, if possible).
• Because of limited resources, gathering original data was beyond the capability of the
NCEA GCRP. Therefore, sites chosen needed to have fairly detailed and comprehensive
data sets already available. Supporting research conducted in the selected location(s) was
considered an additional benefit.
1.2.3. The Portfolio of Case Studies
Three case-study locations were chosen based on the above criteria. The selected
case-study sites were from diverse geographic regions and aquatic ecosystem types, with
different land-use pressures (e.g., agricultural pressures, urban growth pressures) and different
future climate-induced changes (e.g., increased versus decreased runoff). Each site provided
highly valued ecosystem services and had substantial amounts of data and existing research on
which the case-study teams were able to build. Table 1 provides a comparison of some of the key
aspects of each of the case studies, and Figure 1 shows the location of the case studies across the
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United States.
The Maryland case study focused on riverine systems and their associated riparian zones
in four selected watersheds of the greater Washington, DC, metropolitan area. Ecosystem
services of interest involved the maintenance of water quality, fish and invertebrate species, and
primary production and the availability of detritus. Primary stressors of concern include climate
change and land-use change, specifically disturbances resulting from urbanization, increasing
imperviousness in watersheds, and destruction of streamside vegetation.
The San Pedro case study was located in the Upper San Pedro River riparian ecosystem
in southeastern Arizona and northern Sonora, Mexico. This area supports a riparian ecosystem
that maintains biodiversity at the ecotone between the Sonoran and Chihuahuan deserts and the
plains grassland. The area contains one of the richest assemblages of species and supports one of
the most important migratory bird habitats in western North America. The ecosystem services of
interest thus included avian habitat suitability. Primary stressors of concern include groundwater
pumping, climate change, and population growth.
The Sacramento case study was located in the Central Valley of California from the
headwaters of the San Joaquin River in the south to the headwaters of the Sacramento River in
the north. The area's ecosystem services that were the focus of study included the provision of
water for agriculture and instream habitat for Chinook salmon (Oncorhynchus tshawytscha). The
Central Valley winter run of Chinook salmon in the Sacramento River is listed as "endangered"
under the federal Endangered Species Act. The Central Valley spring run is listed as
"threatened." The watershed also provides water to the regional municipal and industrial sectors.
Primary stressors of concern include land-use change, population growth, and climate change.
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Table 1. Comparison of the three watersheds
Size
Flow
Ecosystem
services (and
assessment
endpoints)
Major stressors
(other than climate
change and
land-use change)
Modeling
approach
Maryland
Subwatershed scale
(13-28 mi2)
Variance in daily
streamflow has changed
dramatically over the past
50 years; enhanced peak
flows, and reduced
baseflows are attributed to
increased urbanization.
Habitat suitability for fish
(temperature, siltation,
flashiness, riparian zone
condition, riffle vs. pool
habitat)
Changes in water
temperature, siltation rates,
streamflow, riparian zone
condition, and stress on
aquatic habitats due to
urbanization.
System of submodels on
climate, hydrology,
ecosystem, land-use
economics, and
geomorphology.
San Pedro
Watershed scale
(-2,500 mi2)
A portion of the flow in the
San Pedro River comes
from the groundwater
aquifer, but there is large
seasonal run-off resulting
from heavy precipitation
events during the
"monsoon" season
(July- August).
Avian habitat suitability
Groundwater withdrawals
for agricultural and
municipal uses; increasing
water demand due to
population growth.
System of submodels of
climate, hydrology,
ecosystem, groundwater
flow, and geomorphology.
Sacramento
Basin scale (42,000 mi2 SF
Bay watershed)
Flow maxima typically
occur during the late winter
through spring period and
flow minima (dramatically
reduced relative to peak
flows) in the late summer
and early autumn.
Services related to water
supply (quantity of flow
and seasonality) for
irrigated agriculture and
fish habitat
Instream water withdrawals
for urban populations,
agriculture, and industry.
Linked climate, hydrologic
model with information on
water for fish habitat and
irrigation.
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Study Area Watersheds
Sacramento Study Area
Maryland Study Area
San Pedro Study Area
Figure 1. Geographic locations of case studies across the United States.
The studies' fundamental approaches were similar; all three case studies linked climate,
hydrology, and ecosystem models. At their core, the analytic frameworks of all three studies
were driven by integrated modeling systems that start by simulating the effect of climate change
on hydrologic characteristics, and, subsequently, address how changes in these characteristics
affect ecosystem functioning. Two of the three case studies, Sacramento and Maryland, also used
results of large-scale climate models—known as General Circulation Models (GCMs)—to
provide the bounds for, or to drive, the regional climate-change scenarios. The San Pedro case
study relied on historical data rather than downscaled GCM results because the historical data
provided more information on natural climate variability related to periodic regional-scale
events. In the Sacramento and Maryland case studies, GCM outputs provided the basis for
creating downscaled scenarios of temperature, precipitation, and derivative climate parameters.
The San Pedro case-study team developed climate scenarios that represented a reasonable set of
potential climate trajectories, given natural climate variability and the range of climate change
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projections for the region derived from climate models (SWRAG, 2000). They used a 52-year
daily time series of historic weather data (1951-2002) to create transient climate scenarios for
the period 2003-2102. All case studies used multiple climate scenarios rather than limiting their
investigation to one particular future projection. This attempt to bound the range of plausible
futures was used in recognition of the documented uncertainties inherent in simulating future
climate.
The three case studies all examined climate change along with population and other
land-use-related stressors, but the choices of specific stressors were different. For example, the
Sacramento study included in-stream water withdrawals; the San Pedro case study carefully
examined groundwater withdrawals; and the Maryland study focused on sediment load due to
land-use change. Because of the differences in focus, there were also differences in model
components. In the Sacramento River Watershed, model components were added to simulate
groundwater flow and geomorphology. The San Pedro case-study team developed a model to
simulate the effects of flow changes on riparian vegetation. The Maryland case-study team used
geomorphologic models to simulate changes in sediment load and bed sediment composition.
The relative effects of climate change, land-use change, and other stressors demonstrated
by each of the case-study teams showed a mixed response, with each of the systems exhibiting
different sensitivities based on the region, the current stressors, the management goals, and the
anticipated changes.
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2. CASE-STUDY RESULTS
The following section discusses the three case studies, including background on each of
the regions, goals of the project, major stressors, assessment methods, results, adaptation options
(if analyzed), and how the case studies are applicable to other regions.
2.1. MARYLAND
The team for this case-study assessed the potential combined effects of land-use and
climate variability and change on the composition of the fish assemblages of first- through
third-order headwater streams in four watersheds of the greater Washington, DC metropolitan
area. The watersheds lie primarily within the Piedmont physiographic province, and range in size
from 13-28 mi2—much smaller than the watersheds addressed by the other case studies. These
sites were selected because they have all experienced major changes in land use—but with
differing patterns.
Figure 2 shows the study site locations in the accompanying map (from Nelson et al.,
2009). Three of the four watersheds are in Montgomery County (Hawling River, Northwest
Branch, and Paint Branch). One of them, Cattail Creek, is in Howard County, which has different
growth and planning policies. All four watersheds have similar amounts of remaining forested
land; however, the Northwest and Paint Branches have more residential development, whereas
Hawling and Cattail have more agricultural land. Most of the urban development in these
watersheds occurred since World War II, with additional development episodes in the late 1960s
and early 1970s.
2.1.1. Goals of the Case-Study Assessment
The project's goal was to better understand how the effects of climate variability and
change on stream ecosystems depend on land-use choices in surrounding areas. This
understanding is intended to provide decision makers with information about the ecological
consequences of alternative land-use configurations that will assist them in developing potential
strategies for adapting to climate change and variability.
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,(h
Figure 2. Study site locations (watersheds outlined with specific sites
indicated by black dots), gauging site, and weather station. Within the
watershed boundaries, dark grey represents urban land, light grey represents
agricultural land, and white represents forested land.
2.1.2. Major Stressors
Climate change, land-use change, and land cover change, specifically urbanization,
increases in impervious surface, and destruction of streamside vegetation are associated with
stream degradation at the Maryland case-study sites. Streams, which occupy topographic lows,
collect runoff and sediment discharge, making them highly vulnerable to land-use and climate
change. Urbanization, in particular, is a major stressor on habitats in Maryland, contributing to
changes in aquatic temperature, siltation rates, streamflow, riparian zone condition, and the
availability of riffle versus pool-type habitats for fish (Nelson et al., 2009; Nelson and Palmer,
2007).
Climate change is projected to cause a 2-11.5°F warming nationally by 2100 (Karl et al.
2009), but the consequences of this warming depend on the seasonality of temperature shifts. For
example, fewer—but more intense—storms in summer could produce storm-related heating in
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much the same way that urbanization does. Storm-related heating results from heavy rains that
increase runoff over impervious surfaces, leading to spikes in stream temperatures (Nelson and
Palmer, 2007).
The specific stressors that were modeled in the Maryland case study were air temperature
and precipitation from downscaled GCMs and land-use variables (extent of impervious cover,
percentage forested land, percentage of new construction).
2.1.3. Assessment Methods
The endpoint of interest for this watershed study was the suitability of a stream
environment for selected fish species. Fish assemblage composition was chosen by the Maryland
case-study team as the assessment endpoint because fish are effective indicators of systemic
stressors and are widely used as indicators of environmental quality (Fausch et al., 1990; Karr,
1981).
To understand how changes climate and urbanization, separately and in combination,
affect fish assemblages, the Maryland case-study team integrated five submodels. These models
included downscaled climate projections (daily air temperature and precipitation), hydrology,
geomorphology, water temperature, and fish growth and reproduction. Each of the submodels is
outlined below, followed by a description of the land-use scenarios used for the case study;
additional details are provided in Nelson et al. (2009).
2.1.3.1. Submodels
2.1.3.1.1. Downscaled climate projections
Projections of air temperature and precipitation over the period of 2085-2094 were from
the U.S. Department of Energy/National Center for Atmospheric Research Parallel Climate
Model (PCM; Washington et al., 2000) and the U.K. Meteorological Office Hadley Centre
Model v3 (HadCMS; Gordon et al., 2000; Pope et al., 2000). These coupled atmosphere-ocean
GCMs were run under two sets of future emissions scenarios developed by the
Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios
(Nakicenovic et al., 2000)—the A2 (medium-high within the full range of scenarios) and B2
(medium-low within the full range of scenarios) (see Table 2). The outputs from these climate
realizations were statistically downscaled for the specific location of Rockville, MD. Climate
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sensitivity is a metric that captures the magnitude of the model-simulated increase in global
temperature in response to a doubling of atmospheric CO2 concentration. Present climate is taken
from the years 1995-2004 based on historical simulations by the HadCMS model and
statistically downscaled to match observed historical distributions.
Table 2 Comparison of Maryland baseline and climate change scenarios.
Climate change driver series used in the Forecasted Indices for Fish (FIF) for
baseline and future climate scenarios.
Statistic
Mean annual air
temperature
(Mar-Sept)
No. of rainfall events
in 10 years (>0.1 cm)
Average annual P
Average P event"1
No. of heavy P events
year l (>10 cm)
Max 1-Day/1
Baseline
17.2°C
1,170
112.9cm
1.02cm
5
17.4 cm
Hadley A2
20.5°C
1,087
132.9cm
1.22cm
13
21.1 cm
Hadley B2
21.7°C
1,093
111.9cm
1.10cm
10
26.7 cm
PCMA2
15.5°C
1,104
116.9cm
1.05 cm
3
10.3 cm
PCMB2
15.3°C
1,047
94.1 cm
0.90 cm
0
8.4cm
Summary compared to present:
Average summer T
Total P
Heavy P events
Warmer
Wetter
Increased
Warmer
Increased
Decreased
Drier
Decreased
Source: Nelson et al. (2009).
2.1.3.1.2. Hydrology
The hydrology submodel is a continuous streamflow model that projects daily streamflow
over the course of a scenario to capture flashiness. Three different forms of runoff were
examined: surface runoff, subsurface runoff, and groundwater runoff. The model requires inputs
of daily precipitation and temperature, along with variables giving land-use characteristics and
geology (Nelson et al., 2009).
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2.1.3.1.3. Geomorphology
The geomorphology submodel, a sediment transport model, computes changes to the
stream bed as a function of climate and land-use changes. Output is on a daily time-step and
includes particle size distribution, bedload and suspended material discharge, turbidity, and
interstitial clogging (Nelson et al., 2009). The land-use variables that drive the hydrologic and
geomorphic submodels are discussed below.
2.1.3.1.4. Water temperature
The water temperature submodel uses the methods of Mohseni et al. (1998) to project
minimum and maximum instream temperatures based on a daily air temperature series derived
from the downscaled climate projections, percentage deforestation, and watershed size.
2.1.3.1.5. Forecasted Indices for Fish (FIF)
To model food availability, FIF uses a data series giving daily estimates over the course
of the year of detritus, algae, small invertebrates, and small fishes as food sources. This approach
was taken because there are no calibrated models that predict fish food availability as a function
of flow, temperature, and geomorphic conditions. The data series was developed using literature
values, data from the study sites, and expert opinion. Details are provided in Appendix S2 of
Nelson et al. (2009).
Changes to the baseline values for food resources are driven by changes in temperature
and flow. The model assumes that flashier flow will reduce the abundance of invertebrates and
their foods, and that high summer temperature combined with low summer flow will increase
this effect (Nelson et al., 2009).
Fish spawning and growth vary as a function of temperature and flow (direct effects) as
well as food availability (indirect effect). The spawning and growth results over any 10-day
period are combined into indices, which are then related to a matrix offish traits to predict
vulnerable species and the composition of the fish assemblage under a given scenario. The
indices were validated using an independent data set on fish assemblages across urbanization
gradients. Additional details on the FIF and its various components are given in the
supplementary online material provided by Nelson et al. (2009).
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In turn, outputs of these submodels determine instream habitat conditions. Instream
habitat, along with estimates of food availability, control fish growth and spawning success. In
the final modeling step, the fish submodel calculates indices of spawning days available,
spawning substrate, juvenile growth, and adult growth. These indices are then related to a matrix
offish traits to determine which species are most vulnerable under a given scenario and the
resulting composition of the fish assemblage (Nelson et al., 2009).
2.1.3.2. Land-Use and Climate Change Scenarios
To simulate potential land-use change, three variables were used: percentage impervious
surface, percentage new construction, and percentage of watershed forested. These variables
influence infiltration capacity, sediment input, and water temperature and organic input.
Agricultural land use was not included in the scenarios because little of the remaining land
surrounding Washington, DC is dedicated to agricultural use, and there is little difference in the
hydrologic outputs for agricultural versus residential land use.
The case-study team examined two scenarios of land-use change along with the
four climate change scenarios. The baseline land-use scenario assumed 10% impervious surface,
20% forested, intact riparian buffers, and no on-going construction in the watershed. The
urbanization scenario assumed 30% impervious surface, 2% forested, no intact riparian buffers,
and 2% of the watershed under construction (see Table 3 for details of each of the scenarios).
The baseline scenario represented actual conditions in the study area. In total, 10 scenarios were
examined—1 baseline scenario with present climate and present day urbanization ("Baseline"),
4 climate change scenarios with present day urbanization ("Climate change only"), 1 scenario
with increased urbanization and no climate change ("Urbanization only"), and 4 climate change
scenarios with increased urbanization ("Urbanization + climate change").
2.1.4. Impacts and Findings
Under two scenarios (Hadley A2 and B2), March through September temperatures were
higher than baseline temperatures by 3.2-4.5°C and lower under other scenarios (PCM A2 and
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Table 3 Summary of Maryland's 10 land-use and climate change scenarios
used to project impacts on stream fish assemblages
Scenario
Baseline
Climate change
only
Urbanization only
Urbanization +
climate change
Percentage
impervious
10
10
30
30
Percentage
forested
20
20
2
2
Presence of
riparian
buffer
Yes
Yes
No
No
Percentage
watershed under
construction
0
0
2
2
Climate
Present
Future
Present
Future
Source: Nelson et al. (2009).
B2) by 1.7-1.9°C." Total precipitation showed the same pattern of increases over baseline for
the Hadley A2 and B2 and decreased from baseline for PCM A2 and B2. The projected
precipitation trends were more significant than future temperature trends in their influence on
hydrological and ecological processes (Nelson et al., 2009). HadCMS scenarios projected more
extreme temperature changes and a doubling of scouring extreme precipitation events. The
PCM-based climate change scenarios had relatively little changes in precipitation, less scouring
extreme precipitation events, and minimal changes in temperature.
Using these projected changes in temperature and precipitation, the FIF projected results
for each of the following indices for each species: spawning day availability; spawning substrate;
juvenile growth; washout on eggs and young-of-year; adult growth; feeding efficiency; and
thermal maximum. The pathways that proved to have the greatest impact on fish species from
increased urbanization and climate change were stresses on juvenile growth (from altered
temperature and hydrology), and stresses on adult growth (from altered changes in temperature,
siltation, and food resources). For the nine scenarios that projected changes in urbanization
and/or climate change, species adversely affected through reductions in juvenile or adult growth
numbered between 8 and 29 of the 39 fish species studied. Urbanization alone affected few
species, primarily by reducing adult growth (8 of 39 species). However, climate change alone
affected the most species (22-29 of 39 species, depending on the scenario). Urbanization and
climate change together typically increased the number of stressed species through depression of
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adult growth (2-14 species, depending on the scenario). Pathways for such results are increased
siltation in the PCM-based climate scenarios and increased flashiness in the HadCMS scenarios.
Of those species projected to be affected, urbanization and climate change significantly affect
almost all of the recreationally important species, including trout, bass, and sunfish. Overall,
these results suggest that community composition could change significantly with climate
change and/or increased urbanization, causing a loss of diversity under future projected changes
(Nelson et al., 2009).
2.1.5. Methods and Results Applicable to Other Watersheds
The downscaled climate projections used in the Maryland case study could be used for
other studies in the region. The hydrology, geomorphology, and water temperature models are
transferable to regions where similar processes are dominant, as long as the modeled empirical
relationships are the same and it is possible to reparameterize the models with local data (e.g.,
North Carolina Piedmont). The FIF could be applied to other Piedmont streams and other
watersheds of the U.S. East Coast with a similar species mix. The fish assemblage of the
Maryland Piedmont is more likely to apply to a similar region such as the North Carolina
Piedmont rather than the Maryland coastal plain, even though the latter is geographically closer.
For streams with different fish assemblages, it may be possible to develop a similar model if
local data are available on food resources and on the recruitment, growth, and survival of the
species of interest.
2.2. SAN PEDRO
The Upper San Pedro River riparian ecosystem in southeastern Arizona and northern
Sonora, Mexico (shown in Figure 3) is of critical importance in maintaining regional biodiversity
at the ecotone between the Sonoran and Chihuahuan deserts and the plains grassland. It contains
one of the richest assemblages of species and supports one of the most important migratory bird
habitats in western North America. The biodiversity found along the Upper San Pedro River
exceeds that found almost anywhere else in the United States due, in part, to the fact that in other
regions, many natural habitats have been lost. More than 20 different biotic communities occur
in the basin, and the river sustains three vegetation types that are considered "threatened":
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Fremont cottonwood (Populus fremontii) and Goodding willow (Salix gooddingii) forests; river
marshlands (cienegas); and big sacaton (Sporobolus wrightif) grasslands (Price et al., 2005).
Figure 3: Map of the Upper San Pedro River riparian ecosystem.
The abundance, diversity, and health of riparian vegetation and wildlife in the Upper San
Pedro are strongly influenced by river geomorphology and the hydrologic regime, including the
amount, timing, and pattern of surface and groundwater flows. Channel and river flow conditions
have changed dramatically over time, with accompanying changes in riparian vegetation. Prior to
1850 (approximate), the San Pedro was shallower, with marshes—with longer stretches of
perennial flow than are observed today—and a mosaic of vegetation, including cienegas, sacaton
grasslands, and more patches of riparian woodlands of cottonwood, willow, and ash (Arias Rojo
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et al., 1999). From 1850 to the mid-19th century, there was a period of channel down-cutting
(incision), followed by entrenchment, and the formation of a wide, braided channel resulting
from factors such as reduced soil infiltration due to overgrazing and large floods. Subsequent
declines in floodplain groundwater and high fluvial disturbance in the widened channel
destroyed most of the existing riparian vegetation and the floodplain. After the 1950s, there was
a decline in flood magnitudes and rates of fluvial disturbance, allowing vegetation colonization,
channel narrowing, and formation of a new floodplain. Today, the Upper San Pedro is
characterized by cottonwood-willow forest. Increases in recruitment of these species have been
linked to an increase in the size and frequency of winter floods since about 1960. However,
increased channel narrowing in recent years is now reducing the availability of open substrate for
colonization (Price et al., 2005 and references therein). It should be noted that the San Pedro is
also distinguished from other rivers in the region because it is one of the few that remains
undammed and it is partially ephemeral.
2.2.1. Goals of the Case-Study Assessment
The primary goal of the San Pedro case study was to model the likely effects of climate
change, coupled with existing stressors, on riparian plant communities and associated avian
species in the San Pedro Riparian National Conservation Area (SPRNCA; Price et al., 2005).
2.2.2. Major Stressors
Major stressors affecting the riparian ecosystem of the Upper San Pedro include
groundwater pumping, land use, and, in the past decade, fire. Climate change, through direct
effects on temperature and precipitation and indirect effects on water tables and
evapotranspiration rates, is also increasingly important (Price et al., 2005).
River flow in the San Pedro results from a dynamic interaction between surface and
groundwater flows. As a result of climate variability, surface water flow varies considerably both
between and within years. During periods of low precipitation, the flow in the river comes
primarily from groundwater inflow. During periods of storm flows, the shallow alluvial aquifer
is recharged by the stream. Both low flows (base flows) and high flows (flood flows) are
important for vegetation dynamics. The composition of the riparian vegetation community
changes as the depth of the water table changes because of species differences in depth to
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rooting, drought tolerance, and saturation tolerance. Willow and cottonwood—and particularly
the seedlings of these species—require the shallowest groundwater levels (Stromberg, 1998;
Stromberg et al., 1996).
Because of the importance of groundwater for surface flows and riparian vegetation
dynamics, groundwater pumping is an ongoing concern. Most of the pumped groundwater goes
to agricultural use. According to the Arizona Department of Water Resources (ADWR),
agriculture accounts for approximately 7,500 acre-feet of groundwater extraction annually, while
other end uses, such as residential, industrial, and municipal, consume over 20,000 acre-feet of
groundwater (ADWR, 2005). Although some of the pumped water returns to the aquifer via
percolation, 70% of the water used for agriculture is lost. The primary crops in the area are
alfalfa and pasture, which have low water return rates per unit of water used (ADWR, 2005).
Over the next few decades, agricultural water use in the area is expected to decrease, while urban
water uses are expected to rise (Price et al., 2005).
2.2.3. Assessment Methods
A simulation approach was used to evaluate the potential effects of groundwater
depletion and climate change on riparian vegetation structure and dynamics at three sites along
the Upper San Pedro River. Processes modeled included changes in the main vegetation
communities (including riparian, mesic, and xeric), river baseflow, soil water content, channel
migration, and the incidence and intensity of wildfires. Climate change scenarios were
constructed from historical data, and vegetation dynamics were simulated as a function of the
climate drivers and outputs from models of the primary physical processes influencing
vegetation change, including streamflow, channel dynamics, and fire (Price et al., 2005).
The methods used to develop and implement each of these components of the analytical
system are described below.
2.2.3.1. Climate Change Scenarios
Temperature and precipitation interact to influence the relative success of different
vegetation types. For example, in the Upper San Pedro, a greater proportion of precipitation in
summer may benefit perennial grasses, which have shallow roots and are intensive water users,
and, therefore, benefit from more frequent rainfall during the summer growing season. Species
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with deep root systems, such as mesquite, may be favored when there is more precipitation in
winter, which allows for deeper water infiltration by the start of the growing season. A
combination of high temperatures and low precipitation may lead to high evapotranspiration
rates and water stress for shallow-rooted, intensive water users like grasses. Increases in winter
precipitation would increase recharge, while increased winter and summer temperatures would
reduce recharge and increase evapotranspiration (Price et al., 2005).
To examine these dynamics in a changing climate, the San Pedro case-study team
constructed five precipitation and temperature scenarios for the 100-year period from 2003
through 2102 using a 52-year time series of daily temperature and precipitation from the
National Weather Service station in Tombstone, Arizona. Changes in precipitation and
temperature were linearly applied to the historic data, which were used to preserve the
periodicity of El Nino Southern Oscillation and Pacific Decadal Oscillation events. The
scenarios were designed to correspond loosely to those reported for the southwestern United
States over this century (SWRAG, 2000). Climate change projections suggest an increase in
mean seasonal temperatures of 2-7°C over the next 100 years. While all GCMs broadly agree
with this temperature increase, they differ in their projections for precipitation, and so the
researchers examined both increases and decreases in precipitation (Price et al., 2005).
The five scenarios that were modeled include (Price et al., 2005):
Baseline (historical): no climate change; daily temperature and precipitation data were
generated by repeating the actual 1951-2002 data over the 100-year period 2003-2102.
Warm: progressive temperature warming over 100 years, with a 4°C increase in
maximum daily temperature and a 6°C increase in minimum daily temperature by 2102.
Warm and dry: same progressive temperature warming as the warm scenario and a
progressive decline in winter (nonmonsoonal: October 1-May 31) daily precipitation of
50% by 2102.
Warm and wet: same progressive temperature warming as the warm scenario with a
progressive increase in winter daily precipitation of 50% by 2102.
Warm and very wet: same progressive temperature warming as the warm scenario with
a progressive increase in winter daily precipitation of 100% by 2102.
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2.2.3.2. Simulation of Riparian Vegetation Dynamics
Using a 5-day time step, changes in riparian vegetation were simulated as functions of
changes in streamflow, channel migration, and wildfire in response to the different climate
change scenarios. Vegetation population dynamics (changes in recruitment, growth, and
survival) were modeled at the scale of individual sampling plots (10 m by 10 m) for three sites
representing the range of physical conditions and vegetation composition along the Upper San
Pedro River. All plots began with a 20% cover of both annuals and wetland plants (Price et al.,
2005).
Models of the major geophysical processes (stream flow, channel migration, and fire) that
drive riparian vegetation dynamics along the Upper San Pedro are outlined below, followed by a
description of the vegetation model itself. The output of the geophysical process models are the
key inputs to the vegetation model. Additional details on the models are given in Price et al.
(2005).
2.2.3.2.1. Streamflow
Daily streamflow was modeled using the Soil Water Assessment Tool (SWAT), a
physically based hydrologic model designed to project the effects of land management practices
on water and sediment yield in complex watersheds over long time periods (Srinivasan et al.,
1998). In addition to daily temperature and precipitation, input data for SWAT include soils,
topography, vegetation, land management practices, and parameters representing
streamflow-groundwater interactions. SWAT outputs of daily streamflow were inputs to
MEANDER, the model of channel migration described in the next section.
2.2.3.2.2. Channel migration
The MEANDER model (Odgaard, 1989) used daily streamflow outputs from SWAT to
project lateral channel migration under the different climate change scenarios. MEANDER
models channel migration as a function of channel hydraulics, annual stream power, and spatial
heterogeneity in bank erodibility. Channel migration in the model was calibrated using aerial
photographs of channel locations in 1973 and 1996 and annual cumulative stream power from
daily flows over the period 1973-1996 taken from nearby U.S. Geological Survey stream flow
gages (Price et al., 2005).
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2.2.3.2.3. Fire
To examine the effects of fire on riparian vegetation dynamics, the San Pedro case-study
team modeled fine fuel moisture, probabilities of fire occurrence, and fire intensity as a function
of relative humidity, temperature, wind speed, and precipitation. Fire has become more frequent
along the Upper San Pedro in the past decade, possibly as a result of fuel build-up from removal
of cattle and an increase in winter storms during El Nino years. Because riparian plant species
vary in their rates of resprouting following fire, the intensity and frequency of fire may have
important effects on riparian patch dynamics. In general, saltcedar, willow, velvet ash, and
mesquite show higher resprouting under low-to-moderate intensity fires compared to
cottonwoods. More frequent fires could reduce all trees and shrubs and shift the balance to
grasses. In fact, there is some evidence for higher proportions of grassland compared to riparian
forest and woodland on sites where fire has occurred in the last 10 years (Price et al., 2005).
2.2.3.2.4. Vegetation model
The vegetation model was developed using the STELLA II Dynamic Simulation
Software (Peterson and Richmond, 1996). The model simulates effects of changes in climate
(precipitation and temperature), streamflow, channel dynamics, and fire on the recruitment,
growth, and mortality of the following 10 species and functional groups of southwestern riparian
plants: Fremont cottonwood; Goodding's willow; riverine marsh (cienega); mesquite woodland;
saltcedar shrublands; a hydromesic shrub group; a xeric riparian shrub group; herbaceous
annuals; wetland perennials; and mesic perennial grasses. Climate inputs included incident solar
radiation, air temperature, precipitation, relative humidity, and wind speed, averaged (or
summed) over each 5-day time step of the model. Solar radiation and mean daily temperature
were used to calculate potential evapotranspiration using the Jensen-Haise (Wright and Hanson,
1990) and Hargreaves (Wu, 1997) methods. Soil and plant moisture dynamics were modeled as a
function of precipitation, plant cover and moisture uptake, and potential evapotranspiration. Plant
growth was modeled as a function of light availability (modified by leaf area above the plant),
crowding, air temperature, moisture availability (soil water and groundwater), disturbance, and
plant life history characteristics (Price et al., 2005).
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2.2.3.3. Changes in Avian Biodiversity Resulting from Vegetation Changes
Expert judgment about likely changes in avian biodiversity in response to predicted
vegetation changes focused on 87 abundant bird species in the SPRNCA. The expert used the
relative degree of species' dependences on (1) dominance by riparian species in the vegetative
community; (2) extensive and nonfragmented stands of riparian forest; (3) wetland habitat; and
(4) running or standing water to predict future avian community composition (Price et al., 2005).
In addition to this analysis, likely changes in the relative abundances of five rare bird
species were evaluated using Habitat Suitability Index (HSI) models developed by a biologist on
the project team. The five species were Botteri's sparrow (Aimophila botterii arizonae),
southwestern willow flycatcher (Empidonax traillii extimus), Wilson's warbler (Wilsonia
pusilla), yellow-billed cuckoo (Coccyzus americanus occidentalis), and yellow warbler
(Dendroicapetechid). The southwestern willow flycatcher is an "endangered" species, and
several groups have petitioned the U.S. Fish and Wildlife Service (USFWS) to list the
yellow-billed cuckoo as "threatened" or "endangered" (USFWS, 1981).
HSI models were introduced in the 1970s by the USFWS. HSI models are developed
from available information on the habitat preferences and patterns of habitat use of the species of
interest. The models are considered hypotheses of species-habitat relationships rather than
statements of proven cause-and-effect relationships. The value of these hypothesis-based models
is that, because they can be tested and improved as needed, they lead to increased understanding
of habitat relationships for management purposes. Once the models are verified with field
observations, they can be used to evaluate the likely effects of an actual or potential change in
habitat quality on a habitat's "carrying capacity," i.e., the habitat's capacity to support a species
(USFWS, 1981).
HSI models are developed by the following:
• Identifying the critical habitat variables that affect the habitat's carrying capacity for the
species of interest.
• Establishing relationships between the occurrence of these variables and the carrying
capacity of the habitat. Each variable is assigned a suitability index (SI). This is a score
between 0 and 1, where the former is completely unsuitable habitat (i.e., minimal
carrying capacity) and the latter is optimal habitat (i.e., greatest carrying capacity).
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• Developing metrics that can be used in the field to quantify the occurrence of the critical
habitat components (and, therefore, the carrying capacity of the habitat).
• Developing algorithms that combine the variable scores (Sis) into an expression of the
overall carrying capacity of the habitat. This final score is the HSI and can be between 0
(unsuitable for species or guild) and 1 (optimal habitat).
In the San Pedro case study, HSI models were developed by the project team for Botteri's
sparrow, southwestern willow flycatcher, Wilson's warbler, yellow-billed cuckoo, and yellow
warbler and used to make expert judgments about the likely impacts of predicted vegetation
changes on the habitat's capacity to support these species (Price et al., 2005).
2.2.4. Impacts and Findings
Vegetation modeling indicated that changing hydrology and climate change may
fundamentally impact vegetation in the SPRNCA by fragmenting existing riparian and wetland
communities and leading to their replacement by more mesic or xeric communities (i.e.,
vegetation more typical of the desert matrix). The influence of climate change on pioneer
riparian communities will depend on the magnitude and direction of precipitation changes. A
decrease in winter precipitation will likely result in fewer winter floods, lower rates of channel
migration, and much lower cottonwood and willow recruitment rates. An increase in winter
precipitation is expected to result in larger and more frequent winter floods, higher channel
migration rates, and higher cottonwood and willow recruitment rates. Model results suggested a
decreasing trend in coverage by pioneer woody vegetation across the floodplains of the Upper
San Pedro over the next 100 years. At the same time, results indicated that coverage by later
successional communities such as mesquite, ash patch types, and sacaton grassland are likely to
increase over the next 100 years (Price et al., 2005).
The avian biodiversity modeling projected that 26% of the most abundant bird species
would likely be vulnerable to, and adversely affected by, changes in the vegetative community
due to climate change. An additional 25% could be relatively unaffected, and 43% could benefit.
Results of the HSI models indicated that the species most dependent on the cottonwood/willow
gallery forest would show the greatest projected decreases. Even without factoring climate
change into future conditions, marked changes in habitat quality are projected for two of the
five species. This change is caused by a maturation and contraction of the cottonwood/willow
25
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forest in the middle of this century; the change will result in decreased habitat for the
yellow-billed cuckoo and an increase in habitat for the Botteri's sparrow as the forest is replaced
with grassland and shrublands (Price et al., 2005).
The no change, warmer, and warmer drier climate modeling scenarios all resulted in a
loss of riparian forest and wetlands and their replacement by mesic or xeric vegetation
communities. High avian biodiversity in the SPRNCA is supported by the proximity of riparian
gallery forest and wetland habitats within a matrix of desert scrub and grassland (Price et al.,
2005). Loss of either of the habitats could reduce the biodiversity of the SPRNCA, because the
birds that currently inhabit these areas are expected to be replaced by current occupiers of the
desert scrub matrix. These findings suggest that climate change could have important
implications for the ecosystem services provided by the SPRNCA (Price et al., 2005).
A decline in ecosystem services that sustain ecotourism could adversely impact demand
for those activities within the region. The SPRNCA is a major attraction to wildlife viewers and
ecotourists. If the gallery forest were to be fragmented or entirely lost as is projected under the
three driest climate change scenarios, the area would be less attractive to the public. If future
climate changes more closely resemble the warmer and wetter scenario, adequate water supply to
the ecosystem might help maintain ecosystem services (Price et al., 2005).
Case-study findings indicate that a warmer wetter future climate does not pose as
significant a threat for vegetation as a warmer drier climate projection. The case study did not
separately quantify the effects of aquifer depletion and climate change. Climate change will
cause changes in the ecosystem and aquifer even without water extraction and other forms of
human interaction. The impact of aquifer depletion, however, is expected to be more dramatic in
terms of scale than the effect of climate change alone on the San Pedro River ecosystem.
Together, these two stressors will have a major combined effect (Price et al., 2005).
2.2.5. Methods and Results Applicable to Other Watersheds
The results from this case study and, in particular, the challenges of aquifer depletion are
applicable to other areas. The vegetation, hydrology, and wildlife data inputs used in the models
make them specific to the southwestern United States and other arid environments with
groundwater-dependent riparian systems. Migration is useful in other regions, as long as the
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specific vegetation data are adapted. However, the approach is not applicable to systems where
vegetation uses water from the unsaturated zone (Price et al., 2005).
2.3. SACRAMENTO
2.3.1. Goals of the Case-Study Assessment
The broad goal of this case study was to develop a model for assessing how global
stressors may affect the balance of water supply and demand in the Sacramento River Watershed
and the many ecosystem services in the basin that depend on freshwater. The case study focused
on two services: offstream water supply for agriculture and instream flows for Chinook salmon.
2.3.2. Major Stressors
The Central Valley of California extends approximately 450 miles, from the headwaters
of the San Joaquin River in the south to the headwaters of the Sacramento River in the north (see
this area within the larger San Francisco Bay Delta Watershed in Figure 4). This area of
9
approximately 42,000 mi is referred to as the Sacramento River Watershed. The two rivers and
their tributaries drain into the Sacramento-San Joaquin Delta (Delta), eventually flowing into San
Francisco Bay and the Pacific Ocean. Water from the basin supports a number of highly valued
ecosystem and human use services in the region, including agriculture, municipal and industrial
uses, hydropower, recreation, and aquatic habitats and biota.
Historically, most precipitation occurred in winter (November-April), primarily as snow.
Flow maxima occurred in spring from snowmelt runoff, while flow minima occurred in late
summer. This general pattern prevails, but land use and water development—particularly the
construction of large dams and reservoirs on all of the major rivers—have significantly altered
the basin's natural hydrology.
As the population has grown, agriculture and urban activities have required larger and
larger quantities of the basin's water. Irrigated land is currently stable or decreasing slightly, at
about 1.5 million hectares, but the main crops continue to be those that are water-demanding
(e.g., cotton, grapes, tomatoes, fruits, hay, and rice). In addition to uses within the basin, a
significant amount of water is exported through Delta pumps to satisfy municipal and industrial
demands along the Southern California Coastal Plain and agricultural demands in other basins
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O t\ h Li O .
Sacramento fftVer
Watershed *
Sacrami
San Joaq
Delta
Santa fio
San Francisco
Bay Watershed
San Franci
Pioneer Seamoum
San Joaquin River
lyajershed
" d Si : <
SanLuisObispo"
fe'i
Figure 4: Map of the San Francisco Bay Delta Watershed, which includes the
Sacramento River Watershed.
The rerouting and depletion of basin water supplies have resulted in several major
changes to natural hydrology. Now winter peak flows occur earlier, and spring runoff is
significantly reduced. Summer flows are higher than under natural conditions because of
upstream reservoir releases to meet summer irrigation needs.
Projected climate changes will again change basin hydrology. It is anticipated that more
precipitation in the basin in winter will fall as rain, reducing water storage in the snowpack,
snowmelt runoff in spring, and summer base flows. At the same time, increased air temperatures
will warm surface waters, potentially above the tolerances of the basin's aquatic life.
The model was designed to (1) understand the relationships among stressors and
ecological processes and the aquatic ecosystem services they provide; (2) use this information,
along with water resource models, climate change scenarios, and assumptions about the future
28
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intensities of existing stressors to project effects on the future functioning of these services;
(3) provide stakeholders with information on how valued ecosystem services are likely to be
affected, so that they can make informed decisions; (4) develop appropriate methodologies for
assessing effects on ecosystem services that will be transferable to other large watersheds in
different locations and settings; and (5) provide integrated decision support for issues of
reservoir location, Federal Energy Regulatory Commission dam relicensing, and system
operations to preserve the ecosystem services of interest or of regulatory necessity.
Agriculture is an important activity in the basin. Eight of California's 15 most
agriculturally productive counties are in the Central Valley, which makes it one of the most
important agricultural areas in the world. The main crops grown there—for example, cotton,
grapes, tomatoes, fruits, hay, rice—are generally water-demanding. The annual crop value is
typically in excess of $14 billion, and more than 30% of the total economy is attributed to
agriculture. (California Research Bureau, 1997.)
Another highly valued ecosystem service provided by water in the basin is instream
habitat for Chinook salmon. Chinook salmon populations have declined dramatically over the
last century, primarily because of overfishing, the construction of dams that blocked access to
historical spawning habitats, sedimentation of spawning beds, and water diversions that reduced
flows and increased water temperatures during critical stages in the salmon life cycle
(Yoshiyama et al., 1998).
Suitable spawning habitat for Chinook salmon in the Upper Sacramento River is
currently dependent on releases of cool water from reservoir hypolimnia between May and
September. Without these releases, the water temperatures would exceed the physiological
tolerances of the eggs and juveniles of the winter and spring runs. Reservoir releases also keep
summer water temperatures in the lower river at levels suitable for juveniles moving
downstream. However, if releases of cool waters from upstream reservoirs between May and
September are reduced or discontinued, summer water temperatures in the lower Sacramento
River could reach levels that exceed the physiological tolerances of adult and juvenile salmon.
Climate change will exacerbate these problems. Water temperatures will show additional
increases as air temperatures rise or precipitation and runoff decrease in response to global
warming. It is possible that water temperatures could reach levels that will impair the ability of
salmon to find any suitable cold water habitat.
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The major stressors on water supply in the Sacramento River Watershed are population
growth, land-use change, and, increasingly, climate change. Steady growth in population,
particularly around existing urban areas and transportation corridors, directly affects the demand
for water in the Sacramento River Basin. In addition, changing land use, in particular, the
extension of urban area into other land-use types, stresses water supply and demand in the basin.
Climate change is expected to exacerbate these demands on water (Yates et al., 2006).
The primary problem caused by land-use change and population growth in the
Sacramento River Basin is the transfer of water from irrigated agricultural systems and into the
urban environment (Yates et al., 2006). The scale of water development in California is among
the most substantial in the world, with water often being shifted from one basin to another over
distances of hundreds of kilometers to satisfy water demands. Much of the water in the basin is
exported through pumps in the Delta in order to satisfy municipal and industrial demands along
the Southern California Coastal Plain and agricultural water demands in other basins. Land-use
change and water development—particularly the construction of major reservoirs on all of the
major rivers—has altered surface water hydrology in the basin and created peak flow conditions
earlier in the winter and reduced spring flows. In addition, summer flows are higher than under
natural conditions because operators attempt to meet summer irrigation demands by releasing
water downstream (Yates et al., 2006). Climate change—particularly projected increases in
summer temperatures—is expected to cause an increase in water supply requirements for all land
uses (Yates et al., 2006).
The two major challenges in water management under these conditions are (1) to
overcome the spatial and temporal mismatch between where and when precipitation occurs and
where and when water is needed, and (2) to balance offstream uses for agriculture and urban
areas with instream needs for aquatic habitats and biota.
2.3.3. Assessment Methods
The case-study team applied the Water Evaluation and Planning (WEAP) modeling
system to analyze tradeoffs among offstream and instream water needs. The model recognizes
that water supply is defined by the amount of precipitation that falls on a watershed and is
depleted through natural watershed processes, with evapotranspiration being the first significant
point of depletion. The residual supply is available to the water management system. WEAP is
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thus able to link climate, land-use/land-cover conditions, and water management (Yates et al.,
2006).
WEAP includes a transparent set of model objects and procedures that can be used to
analyze a full range of issues faced by water planners using a scenario-based approach. The list
of issues includes climate variability and change, watershed condition, anticipated demands,
ecosystem needs, the regulatory environment, operational objectives, and available
infrastructure. Biological requirements in the model, such as fish mortality or reproduction, can
be related to projected climate characteristics as well as hydrological and water quality
characteristics (Yates et al., 2006).
In the modeling process for this study, the Sacramento River Basin was divided into more
than 100 subcatchments, groundwater basins, irrigated areas, and urban demand centers in an
attempt to completely characterize the forces that act on water in the basin. A monthly climate
time series from 1962-1998 was used to drive a distributed hydrologic model that simulates
runoff, groundwater-surface water interactions, and consumptive water demands. Water
management infrastructure, including reservoirs, canals, and diversions, was superimposed over
the physical watershed. A verification analysis showed that the model is able to reproduce both
local and regional water balances for the 37-year period, including managed and unmanaged
streamflow, reservoir storage, agriculture and urban water demands, and the allocation of
groundwater and surface water supplies (Yates et al., 2006).
This study evaluated the impact of four climate scenarios on water management in the
region and whether water management adaptation could reduce the potential impacts of climate
change on irrigated agriculture and salmon habitat. The four climate scenarios were derived by
downscaling the output from two GCMs (Parallel Climate Model and Geophysical Fluid
Dynamics Laboratory) and two emission scenarios (A2 and Bl) to a 1/8-degree grid over
California. The A2 and Bl emission scenarios are from the Special Report on Emissions
Scenarios published by the Intergovernmental Panel on Climate Change (Nakicenovic et al.,
2000). The A2 storyline describes a heterogeneous world where local identities dominate,
economic development is regionally oriented, and per capita economic growth and technology
change are more fragmented and slower than in other storylines. The Bl storyline describes a
world where economic growth is rapid and there is convergence among nations, capacity
building, and increased cultural and social interactions. In the Bl storyline, there are rapid
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changes in economic structures toward a service and information economy, with reductions in
material intensity and the introduction of clean and resource-efficient technologies. The
four climate scenarios were (1) Parallel Climate Model with an A2 scenario; (2) Parallel Climate
Model with a Bl scenario; (3) Geophysical Dynamics Laboratory with an A2 scenario; and
(4) Geophysical Dynamics Laboratory with a Bl scenario (Yates et al., 2006).
Simulations also took cropping patterns and irrigation management into account. In
one simulation, cropping patterns and irrigation management remained fixed over the course of a
100-year simulation. In a second simulation, cropping and irrigation management changed with
climate. The case study did not isolate climate and land-use stresses to determine their individual
effects on the system (Yates et al., 2006).
2.3.4. Impacts and Findings
Two of the four climate scenarios predicted a decreasing trend in precipitation over the
next century, with the other two scenarios showing less pronounced changes—one scenario
predicted slightly wetter conditions at the end of the century, and the other showed a decrease in
precipitation in normal-dry years and an increase in precipitation in normal-wet years. All
four scenarios predicted increases in average winter and summer temperatures over the next
century ranging from a lower bound increase of 1.5°C in winter and 1.4°C in summer to the
higher bound of 3.0°C in winter and 5.0°C in summer.
Key hydrologic factors were examined under the four scenarios to determine whether
existing water management was capable of responding to potential climate and land-use changes.
For the first hydrologic factor—annual inflows to reservoirs—two scenarios projected increased
annual inflows to the major reservoirs and two projected lower annual inflows.
The second hydrologic factor was changes in the timing of stream flows. All scenarios
showed earlier stream flows compared to historic conditions, which would have the greatest
effect on those basins dependent on snow melt runoff (e.g., Sacramento watershed above Lake
Shasta).
Persistence of drought conditions, the final hydrologic factor, was projected to be less
severe than the historical record under two scenarios. A third scenario projected that droughts
comparable in magnitude to the early 1990s drought would occur with regularity. The
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fourth scenario projected a very severe drought during the last 15 years of the century (Yates
et al., 2006).
All four scenarios showed an increasing trend in water requirements with time. The
increasing water supply requirements were due primarily to increasing summer temperatures and
increasing crop water demands as summer temperatures increased.
Groundwater pumping was projected to be relatively stable for all scenarios for the
period 1960-2064. In the last period, 2070-2099, pumping increased significantly in dry years
for one scenario when surface water deliveries were less reliable. Aquifers in the region showed
relatively stable fluctuations around a mean for most of the period between 1960 and 2070.
During this period, the surface water deliveries were increasing as a result of growing crop water
requirements, so that groundwater pumping levels were only marginally increased. During the
final period of analysis (2070-2099), however, an extended 10-year drought in one scenario
shifted agricultural water supplies to groundwater. As a result, groundwater levels decreased
sharply (Yates et al., 2006).
Future climate changes, particularly shifts in temperature and precipitation patterns could
lead to further reductions of the Chinook salmon's fragmented habitat. Specifically, increased
water temperatures were projected to result in exceedances of critical spawning and rearing
temperatures, thus jeopardizing the productivity of Chinook salmon (Yates et al., 2006).
The Sacramento case-study team considered two adaptation approaches, one focused on
cropping practices to reduce water demand, the other focused on water management to maintain
suitable instream flows for salmon. The first was incorporated into the WEAP model and
consisted of strategies to adapt cropping practices. The options analyzed included improved
irrigation efficiency and changes in cropping patterns in response to water supply conditions.
The results showed a decline in water supply requirements as improvements in irrigation
efficiency were implemented (Yates et al., 2006).
Adaptation options for salmon focused on managed releases of cold water stored in
reservoirs. The schedule and magnitude of releases can be used to ensure adequate instream
flows. Ironically, more 'natural' and unmanaged systems may provide fewer opportunities for
adaptation to climate change effects (Yates et al., 2006). Because Chinook salmon are coldwater
fish, they may be particularly vulnerable to increasing water temperatures as a result of climate
change. Rising water temperatures in their natal rivers could adversely affect the salmon's ability
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to find suitable breeding habitats, especially because that habitat has already been reduced by
dam construction. However, dams allow scheduled releases of cold water stored in reservoirs,
such that the frequency and timing of these releases could be used to aid salmon survival during
spawning (Yates et al., 2006).
2.3.5. Methods and Results Applicable to Other Watersheds
In most managed water systems, a major challenge is to balance the complex tradeoffs
and interactions of the multiple uses of water (e.g., water for food and water for environment),
some of which are in conflict, and others which are not. The WEAP model framework has
proven useful for this purpose, with the flexibility to apply to multiple locations and systems.
The intrinsic logic behind WEAP is universal and could be easily adapted for other locations
using site-specific data.
Further, the results from this case study would apply to other watersheds that are similar
in character and nature. For example, if agricultural sector water demand is scaled back due to
improved irrigation efficiency and changes in cropping practices, there will be more water for
other sectors. Given that all water resource systems and hydrologic systems are unique, however,
the specific results would not be transferable. In other words, the results would be applicable
qualitatively—but not quantitatively.
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3. FINDINGS AND RECOMMENDATIONS
NCEA GCIA initiated a set of watershed case studies to gain a better understanding of
the effects of global change on aquatic ecosystems and water quality, and to build capacity to
respond to these effects at appropriate levels of decision making. The case studies demonstrated
that certain factors help ensure a sufficient "capacity" for conducting assessments that produce
useful information. The discussion and recommendations below are centered on (1) whether the
assessment processes and results from the studies are useful in furthering our understanding of
global change effects beyond the specific places in which the studies were done and the factors
that would improve usefulness and transference in the future, and (2) the effectiveness of each
case-study team's stakeholder and communication processes and the factors that would enhance
these processes in the future (see Table 4 below for a list of the recommendations).
Table 4. Summary of recommendations for future watershed assessments
Assessment process
Stakeholder process
Provide keystone capabilities and tools to
project teams
Emphasize model linkages to ensure
seamless integration
Carry out assessment activities at multiple
scales
Require explicit uncertainty analyses in
assessments
Build on existing stakeholder relationships
Target selection
Establish credibility
Incorporate incentives for mutually
beneficial results
Design selection criteria to maximize
decision support
3.1. ASSESSMENT PROCESSES AND RESULTS
The first question is whether the assessment processes used by each case-study team are
instructive to other project teams, and whether the climate impacts information generated is
useful to specific decision makers and applicable to other geographic regions. The sections
below discuss the composition of each case-study team and the methods used for facilitating
effective scientific collaborations (see Section 3.1.1); the research design and ways in which
specific results from each of the case studies may be more broadly useful (see Section 3.1.2); the
methodological issues related to the spatial scale of each study and how to address these issues in
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the future (see Section 3.1.3); and each case-study team's treatment of uncertainty and methods
for improving estimation and communication (see Section 3.1.4).
3.1.1. Case-study Team Composition and Management
3.1.1.1. Findings
Given the multi disciplinary nature of the assessments, and the complexity of the models,
all three case-study teams included multiple investigators and disciplines. The San Pedro and
Maryland case-study teams included experts in hydrology, geomorphology, and aquatic and
avian ecosystems. The principal challenge in both of those case studies involved linking a series
of separate models to provide an integrated analytical capability suitable for the assessment
endpoints selected. Both San Pedro and Maryland invested considerable effort in developing new
research approaches that involved modifying existing models and linking those models to
provide a complete assessment capability that started with the physical effects of climate change
and finished with some measures of ecological changes.
The Sacramento case-study team primarily chose hydrologic endpoints (i.e., flows and
quantities of water), and, consequently, balanced their expertise in hydrology with some
expertise in ecology. Rather than developing new models, they selected an existing modeling
framework that integrates water supply, demand, and quality to address the complexity of the
water management system in California (the WEAP model).
The Team Managers/Principal Investigators of all three case-study teams were faced with
a challenging series of tasks, including:
• Guiding their teams through an extensive scoping and method development phase;
• Deciding how to depict climate change and variability in a way that related to the
ecosystem services of concern;
• Developing and implementing plans to engage appropriate stakeholders;
• Implementing a model development and integration phase; and
• Communicating results in a variety of forums and formats.
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Each project manager guided the project based on the particular expertise he or she
brought to the table. Ecologists led the San Pedro and Maryland case-study teams, and many of
the technical advances were related to methods for simulating important ecological processes. A
hydroclimatologist led the Sacramento study, and much of the effort on that study—particularly
in the initial stages of the project—was devoted to developing an innovative technique to
downscale Global Circulation Model results to the regional scale.
One issue faced by all three case-study teams was the need for several "keystone" skills,
especially expertise in interpreting climate change scenarios, working with stakeholders, and
evaluating and communicating uncertainty. To address one area of expertise lacking from some
of the case-study teams, Dr. David Yates, the hydroclimatologist who led the Sacramento
case-study team, acted as an informal consultant to the other two project teams in developing
their climate scenarios. Another missing area of expertise was addressed by the Sacramento
case-study team through the addition of an expert in stakeholder processes who conducted an
evaluation of stakeholder needs, processes, and decision points related to climate change impacts
information. The extent to which each case-study team expressed the need for a set of "key"
skills raises the question of whether future watershed assessments would benefit from some
degree of standardization in terms of expertise, methods, or tools.
3.1.1.2. Recommendation #1—Provide Keystone Capabilities and Tools to Project Teams
As noted earlier, there were several areas where all three case-study teams expended
considerable effort on similar tasks. It is reasonable to expect that other watershed-level
assessments would need to undergo similar processes. When conducting similar assessments in
the future, several useful keystone capabilities and tools to include are as follows:
Tools for converting GCM output to watershed modeling input. The case-study teams
all had an initial focus on reviewing and interpreting GCM runs to develop their climate
scenarios. GCMs simulate temperature and precipitation on short time steps ranging from
15 minutes to half a day. Such data are often stored as averages over longer periods of
time (often monthly), because of data storage constraints. Most hydrologic processes
require daily (or even hourly) inputs over a finer geographic scale and need to be
downscaled on both a temporal and geographic basis. GCM runs are also available for
many different combinations of emission scenarios and climate sensitivities, and it can be
daunting to choose among the scenarios. The lesson learned from these case studies is to
provide expertise to future project teams to aid in selecting, interpreting, and downscaling
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GCM output. Future assessments could use an existing tool or develop a new tool for
handling climate information. For example, one tool developed by EPA is the BASINS
Climate Assessment Tool. This tool provides users flexible capabilities for creating
climate change scenarios that allow users to quickly assess a wide range of "what if
questions about how weather and climate could affect their systems using the Hydrologic
Simulation Program FORTRAN watershed model (U.S. EPA, 2009), and provides case
studies of potential applications (U.S. EPA, 2012).
Tools to develop or apply trend analysis of precipitation and hydrology to
complement GCM output. A simple trend analysis of climate variables may be a
complementary approach to create future scenarios (Denault et al., 2006). Although
conventional precipitation and hydrology analyses of intensity, duration, and frequency
are based on the assumption that there is no underlying trend in the record (i.e., that a
record from 100 years ago has equal relevance to predicting tomorrow's conditions as a
record from 100 days ago), several new powerful statistical techniques exist to evaluate
trends and could be made available to watershed researchers to complement GCM output
(Denault et al., 2006).
Build capacity in keystone skills. Project teams could benefit from having access to
expertise in key areas such as climate scenario development, habitat suitability analysis,
stakeholder facilitation, and uncertainty analysis and communication. To the extent that a
set of assessments begin and end with similar inputs and outputs, it may streamline
assessment processes to provide access to such experts.
For all of these keystone capabilities and tools, the benefit of providing them to the
watershed case-study teams would have to be balanced against the objective of building
broad-based technical capacity and testing alternative approaches, which argues for less, rather
than more, concentration and standardization of expertise.
3.1.2. Research Design, Case-Study Results, and Future Applicability
3.1.2.1. Findings (Research Design)
All three case-study teams developed approaches that relied on linking a chain of
submodels to simulate physical, hydrological, geomorphologic, and ecological components that
ultimately related to ecosystem services. All three of the case-study teams also reported
challenges in coupling the model elements.
The Maryland case-study team invested considerable effort in linking submodels and
developed a paper on the topic (Nelson et al., 2009). The San Pedro case-study team pushed the
state of the art in several of the individual submodels, but those submodels remained largely
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discrete and required considerable effort to provide working interfaces such that the outputs of an
"upstream" module could be used as inputs for a "downstream" module. The Sacramento
case-study team started with a preexisting modeling framework that linked hydrology and water
management. The Sacramento case-study team invested in improvements in the model's ability
to incorporate climate scenarios and represent surface water-groundwater interactions.
Geomorphology took on a central role in two of the three studies (San Pedro and
Maryland). One of the key aspects of climate change—more intense precipitation as well as
longer dry periods—translates to higher high flows and lower low flows in the hydrographs of
streams. These changes, in turn, affect the processes that create transitional ecosystems vital for
certain avian species. They also govern sediment transport and stability, which affect spawning
success for fish. The resulting changes in avian and aquatic habitat were key drivers in the San
Pedro and Maryland studies.
With the exception of the Sacramento case-study team's modeling framework, methods
of linking were primarily functional, in which the models were not significantly modified, but
calculations were coordinated, with certain models' outputs directed to other models' inputs
according to a specified order for the computations. Each of the case-study teams recognized the
value of linking these types of models and expressed an interest in integrating additional models
to add more dimensions to the studies.
These linked sets of models were helpful from both the scientific and decision support
points of view. Modeling system behavior helps to explore uncertainties and identify critical
system interactions and sensitivities. Fully integrated models may also facilitate assessments of a
broader array of decision-relevant questions using multiple scenarios. For example, the
Sacramento case-study team's assessment framework helps decision makers evaluate a number
of different adaptation strategies to identify tradeoffs among important ecosystem services. This
framework, known as WEAP (Yates et al., 2009), is able to provide integrated water resource
management support to the Sacramento region, to the state of California, and to other regions of
the country.
3.1.2.2. Findings (Case-Study Results)
As noted earlier, a "portfolio approach" was used to select case studies and commission
assessments in three distinctly different watersheds with differing ecosystem services, scales, and
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decision-making processes. The Maryland case-study team separately quantified the effects of
land-use change and climate change, but they determined that it was unclear which stressor had a
larger impact; they found that each contributes to the same impacts but in slightly different
proportions. Land-use change provides more sediment due to increased construction and
increased impervious surface, and climate change causes more increased storm flow,
disturbances to the streambed, and variability in conditions than land use. Effects on ecological
processes are thus generally negatively influenced by the projected climate and land-use changes
and, when the stressors are combined, predominantly negative effects emerge. (Nelson et al.,
2009; Nelson and Palmer, 2007.)
The Sacramento and San Pedro case-study teams did not separate the effects of land-use
change and climate change but expressed interest in evaluating these stressors independently in
the future. Sacramento researchers noted that they would like to systematically separate
ecosystem stressors given their particular challenge of moving water out of irrigation and into the
urban environment (U.S. EPA, 2005). The San Pedro case-study team noted that climate change
is not as significant a stressor as aquifer depletion; however, when both stressors are applied
together, there is a synergistic effect. The San Pedro case-study team also acknowledged that
isolating the effects of land-use change and climate change in the future could provide
information about runoff and surface flow (U.S. EPA, 2005).
The Maryland case-study team found that up to three-quarters of the fish species would
be highly stressed under the combined effects of land-use change and climate change and that
this outcome could be mitigated by maintaining riparian buffers and decreasing urbanization.
The Maryland case-study team also concluded that not all ecological processes were negatively
influenced by projected climate change and land-use change; however, when they are combined,
predominantly negative effects emerge. In addition, low-flow modeling indicates that future
precipitation trends will influence hydrologic and ecological processes more than future
temperature trends, and the frequency of low flow events of a given magnitude will increase
under future climate and land-use changes (Moglen et al., 2006).
The San Pedro case-study team found that among their five climate scenarios, the warmer
drier scenario could exacerbate current water use conflicts between the human and natural
ecosystems of the Upper San Pedro basin and could accelerate the decline of cottonwood-willow
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gallery forests. A wetter future could partially mitigate the impacts of human water use (Dixon
et al., 2008).
The Sacramento case-study team addressed the issue of adapting to climate change by
looking at three future alternatives including a simulation without adaptation, a simulation with
increases in irrigation efficiency, and a simulation with improved irrigation efficiency and shifts
in cropping patterns related to the simulated status of available water supplies. The results
showed that improvements in irrigation efficiency led to a decline in supply requirements. When
coupled, the effect of improved irrigation efficiency and a dynamic crop pattern was a decrease
in water supply requirements. In addition, the study showed that the management structures and
practices that adversely affected the fish populations historically may provide an opportunity to
alleviate some of the future impacts of climate change (such as changes in the schedule of water
releases from dams) (Yates et al., 2006).
3.1.2.3. Findings (Future Applications)
All three of these place-based assessments provided impacts information that will be
useful to specific decision makers as they develop management responses. Each case-study team
was able to examine the interaction of climate change with other stressors already present,
particularly land-use change, and was able to conclude that climate change will exacerbate those
effects. Where stressors were examined separately by the Maryland case study, results revealed
that the interactive effects were strongly negative and more apparent than when the stressors
were considered separately.
Even though there are many distinctions in the hydrology and bioclimatology of the
case-study sites and differences in the assessment processes used to achieve specific objectives
and endpoints, findings emerged that can be extrapolated to other watersheds and regions and
that can shape strategies for designing processes for similar assessments. The main ways that
results are more broadly useful are as follows:
1. Extrapolation of the results themselves: individual results may be extrapolated for some
watersheds to similar systems. For example, results from the San Pedro can be
extrapolated to other riparian ecosystems in the southwestern United States that rely
primarily on runoff during the summer "monsoon" season; Maryland results can be
extrapolated to other Piedmont rivers (such as those in North Carolina); the interactive
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effects of climate and land-use change can be generalized to other watersheds, as well as
the results that climate will exacerbate existing effects of stressors.
2. Transferability of models to other watersheds: the San Pedro model, although it is
specific to riparian systems in the southwestern United States, could be applied to other
similar ecosystems, and the riparian evapotranspiration submodel could also be
transferable to specific types of wetlands, such as the Everglades; the WEAP modeling
system may be the most transferable because the intrinsic logic behind WEAP is
universal—it could be produced for other locations with site-specific data over a
relatively short time frame (and has been, as of the release of this report—see
http://www.weap21.org/index.asp7doc = 05).
3. The methods used to link process models across disciplines may be used by other project
teams and in other geographic regions of the country.
4. The insights gained about the assessment process, such as the standardization of methods
for climate scenarios, stakeholder processes, and other topics described below, will be
helpful to any research institution seeking to produce useful climate impacts information
for decision makers (see Recommendation #2 below).
3.1.2.4. Recommendation #2—Emphasize Model Linkages
Given the multi disciplinary nature of these projects and the need for project teams to
develop new modeling capabilities to analyze climate change impacts or opportunities for
decision support, one of the key challenges is to facilitate smooth links between submodels. This
was one of the most difficult challenges for the case-study teams to overcome.
Although "systems thinking" may be considered the norm for conducting watershed
assessments, it may not be sufficient for assuring seamless integration of models. Combining a
conceptual framework of the complete system with an information technology perspective to
plan the detailed integration of modeling components may be necessary for "seamless" coupling.
There are trade-offs between setting up an IT-intensive interface for linked models versus a
"hand-crafted" solution. Regardless of the approach taken, more design work done up front to
clearly define inputs, outputs, and interactions among submodels may help to avoid scale-related
integration issues.
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3.1.3. Complexity of Varying Spatial Scales in Watershed Assessments
3.1.3.1. Findings
Each case-study team worked at a variety of spatial scales, a result both of the
phenomena they were investigating and the scale at which decisions are being addressed.
The case-study team investigating small watersheds in Maryland worked at a
subwatershed scale (13-28 mi2), in part because urban growth is regulated at the county-level.
Individual parcels of land rather than pixilated representations were represented in this analysis,
and surrounding land uses were fed back into subsequent land-use change dynamics for each
parcel.
The San Pedro case-study team examined the upper portions of the San Pedro basin
r\
(2,500 mi ), where most of the remaining perennial or near-perennial river reaches exist, making
this stretch of greatest importance for the ecosystem service addressed in the study: the
maintenance of avian habitat. Model representations were limited to plot-scale information,
however, meaning that the simulations were not run simultaneously for the entire landscape but
only for certain representative patches within it.
9
The Sacramento River Watershed study worked at the basin scale (42,000 mi ) but
designed the study modularly, so that smaller subbasins that performed ecosystem services of
particular value (such as Chinook salmon spawning) were nested separately within the design,
and stand-alone results could be produced for those areas. The primary decisions being addressed
here, including water allocation and the balance of competing legislative and regulatory
authority, occur at the state-level, and, consequently, it was necessary to consider the watershed
as a whole.
One of the challenges addressed by all three case-study teams was that available data may
not be suited to the questions under consideration. For example, the geomorphologic processes
that shape channel migration act at a localized level within a stream reach, but information on the
hydrologic and geologic factors that control these processes may be available only on a much
broader scale. The case-study teams dealt with this issue by developing scenarios and scaling up
their results for sample situations to the larger watershed.
Another important scale issue that the case-study teams addressed was the delivery of
ecosystem services at varying scales and with different levels of "connectedness" to other
resources outside the study area. For example, in San Pedro, with its focus on migratory
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neotropical birds, the birds are dependent on the availability of suitable habitat at other locations
and other times. Similarly, in Sacramento, one of the key endpoints—instream flows to support
salmon—is necessary but not sufficient for sustaining "threatened" and "endangered" salmon
populations. Climate change could affect the other critical resources needed to support these
populations, but to keep the scope manageable, the case-study teams assumed that conditions
outside their study's boundaries were essentially static.
Cash and Moser (2000) suggest that the multiscale nature of global environmental
problems poses fundamental challenges to how both assessors and managers work and interact,
including matching the (spatial and temporal) scales of biogeophysical systems with scales of
management systems; matching the scales of the assessment with the scales of management; and
accounting for cross-scale dynamics in both natural systems and institutions. All three case-study
teams experienced these challenges.
3.1.3.2. Recommendation #3—Carry Out Assessment Activities at Multiple Scales
One approach to consider when conducting a watershed assessment is to carry out
assessment activities at multiple scales. Multiscale approaches provide more useful information
than a focus on any one single scale (e.g., Alessa et al., 2008; Vincent, 2007; Sullivan and
Meigh, 2007, among many others). Benefits of this approach include: (1) better problem
definition, as a single-scale assessment may focus on issues most relevant to that scale;
(2) improved analysis of scale-dependent processes, cross-scale effects, and causality;
(3) improved accuracy and reliability of findings; (4) improved relevance of problem definition
and assessment findings for users and decision makers; and (5) increased ownership by the
intended users (MA, 2005).
One specific method that may be used within a multiple scale approach is the integrated
indicator approach. This involves aggregating vulnerability indicators, sometimes multiple layers
of indicators, into a representative index or indices to represent the vulnerability of the target
region (see Kurd et al., [1999], and U.S. EPA [2011] for examples for water resources). The
integrated indicator approach can provide a simple way to combine biophysical, social,
economic, and environmental data to produce a single value representing vulnerability, allowing
a systematic evaluation of individual and sets of indicators, and to compare geographical or
political units. It can also be useful at the screening level to identify candidates for more
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extensive vulnerability analysis. Screening-level indicator applications provide information
useful at multiple scales: (1) they can provide a national-level picture of how vulnerability varies
across the country; (2) they can limit the number of resource-intensive local-scale assessments
needed; and (3) they can foster discussion at the local level of the suitability of the ranking for
the local community which may, in turn, provide useful information in national policy
discussions.
3.1.4. Estimation and Communication of Uncertainty
The first section below discusses sources of uncertainty, and the second briefly reviews
issues that arose when communicating uncertainty to stakeholders.
3.1.4.1. Findings (Type and Extent of Uncertainties)
There are three sources of uncertainty that could affect case-study results, including
uncertainties about the forcing of climate data, model structure, and model parameter values.
Following the usual practice, climate change uncertainties were addressed using climate change
scenarios. Three different approaches were used by the case-study teams: (1) multiple GCM
realizations (assuming that more common results indicate more probable outcomes), (2) Monte
Carlo-type analysis (Yates et al., 2003), or (3) the use of historical data to bracket the range of
variation for particular climate parameters.
Uncertainties about land-use effects, hydrology, and geomorphology were the primary
sources of structural and parameter uncertainty. For example, the Maryland researchers found
that land use was quite sensitive to regulatory changes, population growth, and income changes.
Once the potential land open for development has been developed, the possible responses by
landowners is unknown, but possible outcomes are intensification of developed areas or
reclassification of previously undeveloped land and further landscape alteration. Additionally,
while land use may be predicted on a large scale with some degree of certainty, the
idiosyncrasies of individual land owners and managers may never be anticipated with complete
predictability. Other sources of uncertainty in the Maryland study included a lack of knowledge
regarding the effects of the interactions of multiple stressors in streams, the biology of
understudied fish species, and predictions of habitat suitability.
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Hydrological responses to changing land use were identified by both the Maryland and
Sacramento case-study teams as primary contributors to overall model uncertainty.
Geomorphological responses were another large contributor to uncertainty, particularly in the
San Pedro watershed, for which management goals are predicated, in part, on the occurrence of
transitional ecological states. These transitional states are highly dependent upon sporadic
hydrological events such as flooding, which transfer to the ecosystem through their
geomorphological effects. The creation of unvegetated areas on channel islands or river banks by
floods allows colonization by plants that would otherwise be unable to compete with the
established plant communities and, thereby, increases overall habitat diversity. With time, these
colonizing plants are replaced by more stable assemblages, and floods create new unvegetated
areas. Any one plot may show little change, but over a larger area, the patchiness of habitat types
allows high avian diversity to be maintained. In general, it is more challenging to predict and
monitor processes associated with unusual or extreme events and transitional conditions, and
analyses of this type tend to be more uncertain than those dealing with processes that are driven
by average conditions.
3.1.4.2. Findings (Methods for Estimating and Communicating Uncertainty)
In communicating to stakeholders the uncertainties associated with climate and land-use
change effects on ecological and water resources, a concern of the researchers was that
uncertainty ranges would undermine the possible contribution of results to the decision-making
processes. At issue was whether managers would be willing to place confidence in results that
are presented as uncertain. The uncertainties could be used to justify setting aside the results,
particularly under conditions in which resources are limited and more pressing matters demand
immediate attention and action.
Another issue involved determining the way in which uncertainty analysis might be
conducted to be most useful to stakeholders. The Sacramento case-study team found that their
stakeholders were interested in "stylized" scenarios. For example, the El Dorado Irrigation
district currently uses the worst 3-year drought on record as the basis for developing drought
plans. To be responsive to and consistent with their existing planning guidelines, the Sacramento
case-study team developed alternative scenarios such as a 4-year drought of similar magnitude to
the 3-year drought but one that is also 2°C warmer.
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The project teams noted that it would be helpful to have guidance on how to characterize
and communicate uncertainty results. In addition, several noted that it would be useful to be able
to compare climate change-related uncertainty to uncertainty from other, more familiar sources
relevant to long-term water resource decision making, (e.g., population, land-use change, per
capita water demand).
3.1.4.3. Recommendation #4—Require Explicit Uncertainty Analyses as Part of any
Assessment
Future assessments should consider carefully how to address uncertainty within the
decision-making context. The data available and the degree of uncertainty related to the decision
at hand may require alternative approaches to a classic uncertainty analysis (Groves and
Lempert, 2007). Several approaches include sensitivity and scenario analyses, and scenario
planning. For the purposes of this report, a scenario may be defined as a plausible description of
how the future may develop, based on a coherent, internally consistent set of assumptions about
driving forces and key relationships (Morgan et al, 2008; IPCC-TGICA, 2007).
Analyses that evaluate the sensitivities in a system should be designed based on the
questions being addressed by an assessment. Approaches such as examining the scientific
literature or eliciting expert judgment may be sufficient to address certain questions. Useful,
though limited, information may also come from observed responses to historical climate
variability. However, analyses of more detailed scenarios may be required in other situations,
such as those in which multistressor impacts are being assessed, or variability is outside the
range of observations. Scenarios may also be developed in which climatic drivers are
systematically and incrementally changed. In all cases, the emphasis is on exploring the behavior
of the system in order to identify the following:
• Significant responses of endpoints to changes in some particular drivers and not others
• Asymmetrical responses of endpoints (e.g., large sensitivities to dry conditions but little
response to wet conditions in response to changes in precipitation,)
• Other nonlinear behaviors, such as large, disproportionate responses of endpoints to
drivers in certain portions of the range
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• Thresholds above or below which particularly severe system impacts occur (e.g., the
amount of climatic warming required to raise water temperatures in a stream to the point
that a cold water fish species cannot reproduce and survive)
Techniques for watershed studies that address uncertainty are available from many
sources (e.g., Johnson and Weaver, 2009; Groves and Lempert, 2007; Moss and Schneider,
2000; Hession et al., 1996). The goal of these approaches is to support improved decision
making by allowing more complete consideration of outcomes and their implications, and to
highlight the tradeoffs among alternative decisions. Rather than avoiding discussions of
uncertainty, uncertainty needs to be recognized as a crucial component of any assessment that is
intended to inform decision making.
With respect to communicating uncertainty, conversations with stakeholders can be
useful and informative rather than daunting. For example, discussing with stakeholders those
management options that are robust over a wide range of potential future conditions can relieve
the burden they may feel to identify "the optimal solution" for a single most-likely future.
Climate change uncertainty may also be communicated using comparisons with more familiar
sources of uncertainty. For example, long-range water resource plans generally make
assumptions on population growth, changes in demand for key uses (e.g., agriculture), and
changes in per capita demand. While these assumptions are sometimes heroic, they are
nevertheless familiar (unlike climate change-related factors). Comparing sources of uncertainty
may help illustrate the similarities between other long-term decisions made in an uncertain
context and climate change uncertainties, perhaps reducing reluctance to incorporate results into
decision making. Regardless of the specific approach taken to analyze uncertainty, future
watershed assessments need to plan for conducting such analyses and then execute the plan.
3.2. STAKEHOLDER PROCESSES
Each case-study research team approached stakeholder inclusion somewhat differently,
though a number of features and impressions were common among them. In general, the
case-study teams relied on existing stakeholder relationships and processes. Interactions with
these stakeholder groups were moderate in their frequency, scope, and intensity. The information
flows were primarily unidirectional, from the case-study research teams to stakeholders—
although stakeholders were given opportunities to provide input on each study's endpoints. A
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kickoff meeting was a common feature among all of the case studies. After that point, the
Sacramento case-study team continued with structured elicitation of stakeholder input.
Stakeholder involvement for the Maryland and San Pedro case-study teams was generally less
structured and more opportunistic after the initial kickoff. All case-study teams found that
stakeholder involvement can be a resource-intensive exercise. This and other challenges the
case-study teams faced in engaging stakeholders are discussed in more detail below.
3.2.1. Defining and Identifying Appropriate Stakeholders
3.2.1.1. Findings
For each case-study team, the concept of stakeholder engagement initially included a
wide array of individuals from decision makers to nongovernmental organizations to interested
citizens. Over time, the case-study teams became more sophisticated in their understanding of
the types of stakeholder interactions that were productive and refined their processes to reflect a
targeted and focused approach. Without such targeting, the case-study teams found that
continuing a meaningful dialogue with a broad array of stakeholders could be paralyzing to the
assessment process.
The Maryland case-study team initiated a broad-based introductory meeting for
stakeholders. Professional, academic, and EPA personnel were the initial contact points for
assembling this group. The goal of the meeting was primarily information dissemination from
the researchers to interested parties. Subsequently, the case-study team developed a close and
interactive relationship with the Montgomery County Department of Environmental Protection
that led to an exchange of data and some collaboration and incorporation of researchers' findings
into a wider planning context. Interactions were focused primarily on this stakeholder group
throughout the rest of the assessment process (U.S. EPA, 2005).
Researchers in the Upper San Pedro Basin began work in a setting that had an active
stakeholder group—the Upper San Pedro Partnership (USPP). The USPP is a consortium of
local, state, and federal government organizations, Fort Huachuca Army Base, businesses,
citizens, and conservation groups. The USPP works to develop decision support tools for
analysis of alternative water management regimes, and members of the case-study team became
participants in this ongoing process. Additionally, their affiliation with the Sustainability of
Semi-Arid Hydrology and Riparian Areas (SAHRA)—a National Science Foundation-supported
research center at the University of Arizona—provided them with indirect access to stakeholders.
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The San Pedro case-study team made study results available to the USPP and SAHRA and their
stakeholder organizations.
The case-study team working in the Sacramento River Watershed sought to identify
stakeholders engaged in ongoing decisions regarding water allocations. The Sacramento
case-study team started by assembling a Technical Advisory Panel formed of regionally-based
academics from the physical, ecological, and economic sciences. Meetings with this Panel
occurred at the beginning, middle, and end of the investigation to gather input on other experts to
consult with and to refine the development and application of their modeling framework.
Additionally, a consultant was brought on board the Sacramento case-study team to interview
other high-level water and ecosystem management organizations in the Sacramento area in order
to make strategic recommendations regarding potential applications of their research. This effort
resulted in meetings with several other decision-making organizations and follow-on analyses to
support their decision processes. The case-study team found that the key to establishing working
relationships with stakeholders was to demonstrate that their work was relevant to the decisions
at hand, scientifically credible, and legitimate as an approach to climate change analysis. The
Sacramento case-study team also stressed the importance of finding an advocate among the
participating stakeholders. One person who acts as a champion for collaborating with researchers
and participating in the assessment process can help sustain and facilitate the relationship (U.S.
EPA, 2005).
3.2.1.2. Recommendation #5—Build on Existing Stakeholder Relationships, Target Selection,
and Establish Credibility
Research case-study teams already work with stakeholders in many areas and have
developed long-standing relationships with decision makers, and can build on these existing
relationships when seeking input from stakeholders. Strengthening existing relationships will
take less time and resources than trying to establish new relationships with numerous
stakeholders. Such existing stakeholder groups have also demonstrated a sustained and ongoing
interest in an issue or issues for which they were formed, and if those issues are related to the
focus of a new case-study research team's assessment, than they may bring that sustained
engagement to those issues as well. Further, existing relationships can open doors to meeting and
collaborating with new stakeholders who may be similarly interested in study findings. In much
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the same way that the selection criteria for this set of projects involved availability of existing
data, future projects may also benefit from a selection criterion to evaluate availability of
existing relationships.
Streamlining and focusing stakeholder-related efforts is necessary and desirable.
Effective stakeholder interactions are those that produce results that directly support policies.
The case studies showed that stakeholder relationships may not need to extend to all potentially
interested members of the lay public; instead, they should target only specific decision makers
who have an identifiable stake in the study's goals. Working closely with decision makers to
supply information based on their needs and demands may also help facilitate later transferability
of results and processes because the questions being addressed are likely to be relevant to
decision makers elsewhere. An additional advantage when targeting and engaging stakeholders
interactions might be derived from developing collaborative working partnerships with members
of the decision-making body where possible, to gain their interest and trust in the assessment
results. A working partnership builds technical capacity within the decision-making body that
increases the likelihood of climate change impacts being considered beyond the particular
assessment.
When beginning to engage stakeholders, the first step may need to be establishing
credibility—credibility of the science underlying the methods and models to be used, and
credibility of the planned analysis to be useful to the decisions at hand. The public debate on
climate science has been polarizing, and its relevance to issues on the ground difficult to discern
for the average person. So credibility, or the level of trustworthiness and authority that
stakeholders perceive a project team has related to the work at hand, is key to producing results
that are used in a decision-making process. The project team must set aside time to demonstrate
to decision makers that their models have been reviewed and validated by others, experts in the
field corroborate the methods and analytical approach, and hard evidence exists to support all of
the above. Without credibility, the results may be easily dismissed.
3.2.2. Maintaining Stakeholder Processes
3.2.2.1. Findings
Stakeholders engaged in each case study had diverse views on which services should
receive highest priority for study resources. Case-study teams had to balance those competing
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stakeholder interests with their own research interests. The case-study team members recognized
the dilemma that the primary focus of many scientists—credibility—requires academic
achievements that can come at the expense of spending time with stakeholders to prove the
credibility and relevance of their work to decisions. While stakeholder interactions increase the
likelihood of a project's usefulness, maintaining those interactions can be onerous and
resource-intensive, and thus, come at the expense of other priorities. The inverse of this
challenge is also true: managers do not necessarily recognize the relevance of research
(especially research on long-term problems), often deeming it merely an academic exercise with
no application to their pressing concerns.
Climate change is a particularly acute example of this situation. All research case-study
teams reported at the time of these studies that climate change was not recognized by managers
and decision makers as a primary concern that must be addressed within a relevant timeframe.
Similarly, it may not be clear to them that investing time in climate change-related work could
help in addressing more immediate concerns. Thus, neither side (researchers nor stakeholders)
may be willing or prepared to participate in collaborative exercises that require sustained
interactions over the lifetime of a study, especially a study with results that do not seem relevant
in the near-term.
3.2.2.2. Recommendation #6—Incorporate Incentives for Mutually Beneficial Results
Sustaining researcher and stakeholder interactions throughout an assessment process will
require creating incentives for both parties. Example principles that need to govern a project
team's approach to a study may help ensure that both stakeholders and researchers commit to
long-term engagement. These principles include the following:
1. Empower stakeholders: Stakeholders need to have defined roles and responsibilities in
the study process, with representation rather than marginalization of the various interests.
Stakeholders' views and contributions should be considered, responded to, and if
appropriate, integrated into an assessment, thus making the participatory approach a
means of encouraging contribution and cooperation among the different stakeholder
groups. Seeking a collaborative role (working partnerships) for stakeholders, as
mentioned in the previous recommendation, is an effective way to empower them and
ensure continued engagement. Participatory needs assessment, collaborative research,
and mutual exploration of results represent "best practices" for stakeholder processes.
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2. Motivate stakeholders: As mentioned in the previous recommendation, case-study
teams need to demonstrate how their analysis will support effective solutions to real
problems (a component of establishing credibility) and how stakeholder participation in
the process will add value to the results. Elicitation of all views and timely and thoughtful
consideration of them, along with responses that address their expressed needs and
concerns will help to increase their motivation.
3. Be transparent and communicate often: Case-study members need to be accessible and
communicate in plain language their methods, approach, results, assumptions,
uncertainties, etc. throughout the assessment to build stakeholder awareness and support.
They must also provide stakeholders access to results and develop their capability to
share the information with their own organizations and with broader stakeholder
audiences. This will widen the sphere of support for the study and its results. Information
sharing can happen through printed materials (such as research reports, workshop
proceedings, presentations, fact sheets, maps, and posters) or other more innovative
media (such as audio or visual podcasts). These materials need to be designed with all of
the relevant audiences in mind, because these audiences may be as disparate as high level
politicians and citizen farmers.
4. Be flexible and innovative: The project team needs to be flexible and innovative with
respect to responding to stakeholder priorities and interests as assessment goals, targets,
methods, and endpoints are established. Flexibility can stimulate the design and
implementation of innovative analytic approaches and solutions and encourage
continuous improvement in the assessment process.
5. Recognize and reward stakeholders: It is key that the case-study team recognize and
reward exemplary efforts by stakeholders to engage and contribute to an assessment
process and promote or use results. This may be done in many ways, but should include
feedback to the stakeholder's organization on the contribution a member is making to the
assessment process.
6. Track success: Develop indicators to track the success of the engagement process. Then
note responses to engagement incentives to understand what works best and what needs
to be improved. Indicators may include the number of meetings attended, the continuity
of participation of individuals and groups, the degree of information shared by
stakeholders to those beyond the established members, number of conflicts that arise, and
amount, degree, and type of feedback received from members. Additionally, evaluating
other groups' stakeholder processes may provide valuable information that can highlight
potential barriers, opportunities, and practical lessons that a case-study team can use in its
own processes.
7. Build local capacity: To make the study useful beyond the results themselves,
case-study teams should consider building local capacity to conduct their own analyses
through providing technical assistance and training. If any stakeholders are interested,
providing such assistance will engender good will, increase the capacity of communities
to respond to climate change, and catalyze stakeholder participation in any future studies.
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3.3. RELEVANCE OF IMPACTS TO DECISION MAKING
The Maryland and San Pedro case-study teams focused primarily on conducting impact
assessments—determining the effects of global change (including climate change and land-use
change) on water quantity and quality and the consequences for aquatic ecosystems. These
assessments made significant contributions by linking multiple models to better understand
stressor interactions and responses. Although assessment results did not immediately and directly
inform specific decisions, they provided a foundation on which subsequent work can build to
inform future decisions. Those decisions will have to be based on an evaluation of alternative
policies that prove to be robust across a wide variety of potential future climatic changes and
ecological responses.
The Maryland case-study team found that decision makers at the county level
(Montgomery County) were very interested in the land-use change component of the case study.
Montgomery County officials were focused on problems they are facing in the immediate term
and took a special interest in the findings regarding nutrient concentrations in various streams.
They were pleased to see evidence that riparian buffers have a definite impact on those
concentrations. They have used the study findings to validate research they have in progress and
recommendations they have already put forward. The Maryland case-study team's findings also
reveal the importance of considering climate change. One important area in which to do so is
stormwater management. Facilities that are being built or retrofitted need to account for potential
changes in the intensity of future rainfall events, because such events could affect their
performance (U.S. EPA, 2005).
The San Pedro case-study team's findings were used by the Bureau of Land Management
(BLM) and water resource managers to assess flow rules for reservoir releases from a dam in the
middle San Pedro area. The San Pedro case-study team's results regarding loss of water in the
system led to a BLM decision to reintroduce beaver in an attempt to impound and detain water
rather than letting it flow downstream. However, the BLM decision is unusual. In general, the
San Pedro case-study team noted that a number of obstacles exist for the incorporation of study
findings into the decision-making process, including the uncertainty inherent in climate change
projections, other factors that take precedence in management decisions, and sometimes politics
(U.S. EPA, 2005).
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With a second phase of funding, the Sacramento case-study team identified key
water-related decisions and then tailored their analytical work to meet the needs of decision
makers. They consulted stakeholders to develop a list of ongoing decision-making processes in
the California water system that might be sensitive to climate change. The list was then narrowed
to include only decision-making processes that met three criteria (Purkey et al., 2007):
• The success of a project to be implemented would be strongly influenced by hydrologic
variability.
• The investment in a project would be substantial enough to merit the consideration of
climate change impacts.
• Some segment of the stakeholder community was concerned about the potential impact of
climate change on the project.
This second round of funding enabled the Sacramento case-study team to produce results
for the following decision-making processes: (1) the Integrated Regional Water Management
Plan for the Consumes, American, Bear, and Yuba watersheds; (2) the California Department of
Water Resources' 5-year water planning process (Bulletin 160); (3) an assessment by several
water utilities generating hydropower in the American river basin of how vulnerable they are to
climate change and their ability to meet more stringent inflow water demands; and (4) the 2006
Climate Action Team Final Report to Governor Schwarzenegger and the California Legislature.
3.3.1.1. Recommendation #7—Design Selection Criteria to Maximize Decision Support
One of the recurring themes in this report is that the case studies were quite thorough and
innovative in assessing climate change impacts but were somewhat more limited in providing
direct decision support. It may be because selection criteria were dominated by choosing sites
with a good foundation of existing data and models so that impacts could be assessed as
efficiently as possible. For future watershed assessments, it may be useful to modify the selection
criteria to emphasize case studies (1) where it is clear that decisions are being made that are
sensitive to climate change, and (2) where there are existing relationships with decision makers
that would enable the project team to provide relevant decision support products.
Another factor that should be reevaluated in terms of selection criteria and study design
relates to scale. The research case-study teams noted that there were some mismatches between
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available data versus the scale of data needed to support assessments and decision-making
processes. All three case-study teams were able to bridge the gaps. Nevertheless, in developing a
strategy for future work, it would be useful to consider the scale at which GCM and
watershed-level information are available, the scale at which key endpoints are assessed, and the
uncertainty introduced by bridging the gap, to assure that it will be feasible to produce good
science and sound decision support.
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4. CONCLUSIONS
The case-study approach yields richness of detail in terms of methods and results, and it
propels a research team well up the learning curve on climate change issues. Because conducting
case studies requires linking models from multiple disciplines in some fashion to complete
assessments and provide useful results, this approach has proven extremely effective in both
pushing forward the state of the art of impact assessment and characterizing the potential effects
of climate change and land-use change on ecosystem services to support adaptation planning.
It is important to ensure that capacity for doing assessments is in place before the project
starts. As discussed in Section 3, there are a number of critical factors that ensure success for
impact assessments, including good data, good models, clear goals, appropriate technical
expertise, and public awareness of and engagement in the issue. Identifying that these critical
success factors are in place before launching an assessment will help determine if there is
sufficient capacity to undertake such an assessment.
Assessments may be initiated to achieve a variety of different goals. If the goal of an
assessment is to inform specific decisions, then those decisions should be the primary guide for
selecting endpoints and processes to be modeled. To leverage limited resources, the assessment
community could also think about designing assessments that can inform a broader set of
decisions and decision makers in different regions and watersheds with similar goals and
environmental issues. The ability to transfer the assessment methodology and model results is
more likely if goals are defined upfront and the assessment approach is decision-relevant.
Project teams also need to address uncertainty. However, this can be a difficult task if the
expression of uncertainty is perceived by the decision maker to render the results unusable.
Understanding how to address uncertainty in an appropriate and meaningful way to inform
decision making can be challenging but can be made more tractable by focusing on those
uncertainties that matter to decisions and identifying robust management options across those
uncertainties.
Moving forward, it may be constructive for case-study teams to develop a formal
framework for assuring that assessments are decision-driven, not necessarily by early and
frequent exposure to a broad set of stakeholders, but instead by a focus on a narrow set of
decisions and stakeholders where the information will be most useful. In addition to adopting the
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recommendations found in Section 3, case-study teams may also want to use the following
questions to help establish assessment priorities:
1. Are the decisions (e.g., about choices of management actions) likely or unlikely to be
affected by climate change?
2. If the decisions are likely to be affected by climate change, can they (the particular
management actions) be modified/adapted to ameliorate climate change impacts?
3. If the decisions can be modified/adapted to ameliorate climate change impacts, do they
have short or long planning horizons, implementation periods, or lifespans?
Decisions, or management actions that are affected by climate change and that can be
adjusted to ameliorate impacts present opportunities for effective adaptation, provided the right
scientific information can be offered as to how management actions should be modified/adapted.
If management actions have short planning horizons and/or lifetimes, than providing scientific
information to appropriately adjust those actions becomes less critical than if those same actions
are long-lived. Ongoing research and assessments that directly inform such long-lived decisions
would thus be particularly useful.
The questions above that are intended to focus assessments on providing key,
decision-driven information can build the capacity of decision makers to better respond to global
change impacts on water quality and aquatic ecosystems, but there is still much work to be done
to understand all of the elements needed to make information as useful as possible. Future
projects will afford the opportunity to learn more about how to best address all of the challenges
identified in this report (and more challenges that will likely emerge) to improve the usefulness
of assessment results.
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