Compendium of Tools and Methods to Estimate Environmental Benefits for Nature-Based Solutions Environmental Benefits Related to Water Quantity, Climate Mitigation, Air and Habitat


EPA-832-R-24-005
November 2024

United States
Environmental Protection
Agency

A Compendium of Tools and Methods
to Estimate Environmental Benefits for
Nature-Based Solutions

Environmental Benefits Related to Water Quantity,
Climate Mitigation, Air and Habitat

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A Compendium of Tools and Methods to
Estimate Environmental Benefits for
Nature-Based Solutions

Environmental Benefits Related to Water Quantity, Climate Mitigation, Air and Habitat

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Acknowledgements

This document was prepared by the U.S. Environmental Protection Agency Office of Water/Office of
Wetlands, Oceans and Watersheds/Nonpoint Source Management Branch.

Tetra Tech assisted with editing and formatting the document.

Reviewers included staff from the U.S. Environmental Protect Agency Office of Water and Office of
Research and Development.

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Acronyms and Abbreviations

ac-ft	acre-feet

ac-ft/yr	acre-feet per year

BMP	best management practice

BRAT	Beaver Restoration Assessment Tool

CH4	methane

CN	curve number

C02	carbon dioxide

CSU	Colorado State University

gal/yr	gallons per year

GHG	greenhouse gas

GSI	green stormwater infrastructure

HMI	Heat Mitigation Index

in.	inches

kg	kilograms

kg C/m2	kilograms of carbon per square meter

kg C/yr	kilograms of carbon per year

LID	low impact development

m3/yr	cubic meters per year

MAR	managed aquifer recharge

Mgal/mi2/y"	million gallons per square mile per year

N/A	not applicable

N20	nitrous oxide

NBS	nature-based solution

N02	nitrogen dioxide

03	ozone

PLET	Pollutant Load Estimation Tool

PM2.5	particulate matter less than 2.5 microns

S02	sulfur dioxide

SWAT	Soil and Water Assessment Tool

SWMM	Storm Water Management Model

USDA	U.S. Department of Agriculture

USFS	U.S. Forest Service

USGS	U.S. Geological Survey

W/m2	watts per square meter

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Contents

Acknowledgements	2

Acronyms and Abbreviations	3

Introduction	5

What are Nature-based Solutions and Environmental Benefits?	5

Compendium Purpose, Scope and Organization	5

Water Quantity Benefits	7

Water quantity method and tools	9

Climate Mitigation Benefits	11

Climate mitigation tools	13

Air Benefits	14

Air quality improvements	14

Regional scale air quality tools	14

Local-scale considerations for air quality benefits	15

Ambient air temperature reduction	15

Ambient air temperature reduction tools	16

Habitat Benefits	17

Habitat assessment tools and metrics	18

Conclusion	19

References	19

Appendix A: Restoration versus Protection Actions	22

Appendix B: Literature Review - Systematic Abstract Screening	23

Methodology	23

Results	25

Appendix C: Referenced Equations	26

Tables

Table 1. Summary of environmental benefits covered in the compendium with water quality as the

primary outcome	7

Table 2. Water quantity-related benefits, estimation tools and methods	8

Table 3. Climate mitigation-related benefits and estimation tools	12

Table 4. Air quality benefits and estimation tools	14

Table 5. Air temperature reduction benefits and estimation tools	16

Table 6. Habitat related benefits, estimation tools and metrics	17

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Introduction

State programs, cities and local communities develop plans and implement best management practices
to address water quality impairments. Some best management practices may fall under the umbrella of
nature-based solutions and provide social, economic and environmental outcomes, or benefits to
communities and watersheds. Environmental benefits may be of particular interest when considering
hazard mitigation and offsetting the impacts of land use change. The U.S. Environmental Protection
Agency developed this easy-to-use resource for states, Tribes, local watershed groups and others
interested in estimating environmental benefits, beyond water quality, at the planning level. This
compendium connects urban and agricultural nature-based solutions to publicly available tools and
methods that quantify environmental benefits related to water quantity, climate mitigation, air and
habitat. The compendium will be updated periodically as new resources become available.

What are Nature-based Solutions and Environmental Benefits?

Land use changes and urbanization disrupt the natural hydrologic cycle and cause cascading effects such
as degradation of water quality, localized and riverine flooding, increased air pollution and urban heat
islands. These impacts are further exacerbated by climate change. Holistic solutions to mitigate these
impacts need to integrate traditional gray infrastructure (e.g., storm pipes) with management practices
that rely on natural processes (e.g., floodplain restoration and urban tree canopy).

The EPA defines nature-based solutions (NBS) as actions that protect, conserve, restore and sustainably
manage natural or modified ecosystems. They use natural features or processes to address public health
and environmental challenges while providing multiple benefits to people and nature. NBS encompass a
wide range of actions that may include planning, design and maintenance of engineering practices that
restore, use or enhance natural processes (e.g., green infrastructure, agricultural conservation practices
and coastal restoration) or protect natural features to preserve ecosystem function (e.g., wetlands,
forest, riparian areas and coral reefs).

NBS are often selected and designed to achieve a primary outcome while simultaneously delivering
additional benefits. For the purposes of this document, environmental benefits occur when the design
of NBS achieves benefits beyond the intended primary function of restoring or protecting water quality.
For example, cover crops planted on an agricultural field to control erosion also provide carbon
sequestration benefits. Other common terms used to describe environmental benefits include co-
benefits, ecosystem services, multiple benefits, stacked benefits, ancillary benefits and climate mitigation
benefits.

Compendium Purpose, Scope and Organization

The federal government has scaled up resources, funding and support to advance the implementation
of NBS. This includes historic investments through the 2021 Infrastructure Investment and Jobs Act
(P.L. 117-58, Nov. 15, 2021), also known as the Bipartisan Infrastructure Law, executive orders
(e.g., EO 14008 and EO 14072) and policy directives such as the White House Nature-Based Solutions
Roadmap. NBS align with Clean Water Act goals to restore, protect and preserve water quality and
the EPA's 2022-2026 Strategic Plan to accelerate resilience and adaption to climate change impacts.
Other federal agencies, such as the Federal Emergency Management Agency and the U.S. Army Corps of
Engineers, support and prioritize planning and implementing NBS to achieve natural hazard mitigation

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and resilience goals. When managing nonpoint sources of pollution, aligning goals related to NBS in
hazard mitigation plans and watershed-based plans help planners to leverage activities of mutual
interest and achieve multiple benefits (i.e., water quality and resilience).

What is the scope? This compendium summarizes tools that grantees and sub-grantees may use at the
planning level to quantify and communicate environmental benefits of NBS when implementing
restoration- and protection-based management practices with funds from EPA's CWA Section 319 Grant
Program and the Bipartisan Infrastructure Law, which funds the Gulf Hypoxia Program.1 In addition, this
resource may be valuable to others implementing NBS. During project planning, grantees, sub-grantees
and communities may need to identify and quantify a project's primary outcome and other benefits
(Table 1). However, informational resources that connect specific NBS to existing methods or tools that
help quantify environmental benefits are lacking; this compendium aims to address that gap and
presents details of varied methods and open-source tools. The EPA assessed a wide range of resources,
including white papers, peer-reviewed journal articles, government web pages and other technical
resources, to compile useful and constructive information available on NBS and environmental benefits.
Appendix B discusses a component of the literature review. In general, users of the compendium can
apply these relatively simple quantification methods and tools throughout the contiguous United States.
This compendium is intended to be an informational resource and does not impose any binding
requirements on grantees. Users who are considering applying any of the tools discussed here for
programmatic or regulatory purposes should connect with their EPA Regional Office or State Regulatory
Program on whether the tool(s) are appropriate to use.

Primary outcomes and additional environmental benefits will vary depending on the goals and factors of
integrating NBS into a watershed. Table 1 lists benefit categories and specific environmental benefits
most common in the Section 319 program. The list is not exhaustive but will be updated periodically as
new tools and resources develop. Because water quality improvements are the primary driver of Section
319 and Gulf Hypoxia Program projects, water quality is not listed as a benefit in Table 1. The EPA's
Handbook for Developing Watershed Plans to Restore and Protect our Waters and Green Infrastructure
Modeling Toolkit web page provide an overview of watershed models available to estimate pollutant
load reductions associated with NBS implementation for urban and agricultural land uses (EPA 2008a,
2023).

How is the document organized? This compendium is organized into four main sections specific to the
benefit categories presented in Table 1. Each section consists of two parts. The first part presents a
summary table that connects NBS to identified environmental benefits, quantification methods or tools,
reported units and applicable project scale. The second part provides a brief description of each method
or tool and points users to additional resources.

1 "Restoration" refers to actions implemented to reduce existing pollutant loading to waterbodies, whereas
"protection" refers to actions specifically implemented to preserve existing natural lands to prevent future
pollutant loading to waterbodies. Refer to Appendix A for additional clarification.

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Table 1. Summary of environmental benefits covered in the compendium with water quality

as the primary outcome

Benefit Category	Specific Environmental Benefits

Water quantity

•	Runoff reduction

•	Runoff prevention

•	Groundwater recharge potential

•	Rainfall interception

Climate mitigation

•	Carbon emission reductions

•	Carbon storage

•	Carbon sequestration

Air

•	Air quality improvement

•	Ambient air temperature reduction

Habitat

•	Improved habitat scores or indices

•	Aquatic connectivity

•	Habitat creation

•	Riparian shading

Water Quantity Benefits

Some NBS capture and retain runoff to minimize the volume of runoff entering rivers and streams and
reduce flooding risk. Runoff captured by NBS can be managed through natural hydrologic processes,
such as evapotranspiration and infiltration, or stored for reuse. Table 2 highlights two methods and five
tools that can be used to estimate water quantity-related benefits associated with urban and
agricultural NBS.

The water quantity-related benefits considered here include the following:

Runoff volume prevented, which refers to preventing increased runoff as a result of future land
use changes relative to runoff generated from existing natural land cover.2

Runoff volume reduction, which refers to runoff that is captured, intercepted, stored and

a0a

DQU reta'nec' by restoration-based NBS. Captured runoff volume can be subsequently managed
through processes of infiltration, transpiration and evaporation or reused.2

Groundwater recharge potential, which applies to systems that capture and introduce runoff





into the subsurface for infiltration and eventual migration to the water table.2

Rainfall interception, which describes the amount of precipitation captured by vegetation.2

Icons made by Freepik from www.flaticon.com.

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Table 2. Water quantity-related benefits, estimation tools and methods

Intervention
Type

Method/Tool

Lead Agency

Applicable NBS

Benefit

Units

Scale

CN Method

N/A

Easement/land
conservation

ac-ft/yr

Varies
(site to

c
o

watershed)

u
-------
Water quantity method and tools

The curve number (CN) method is an empirical method developed by the U.S. Department of
Agriculture and is widely used to estimate the runoff response for a particular land use area (USDA
2004). The equation estimates runoff amount (Q, in.) as a function of rainfall depth (P, in.), potential
maximum retention after runoff begins (S, in.) and initial abstraction (la, in.) (Equations 1-3 in Appendix
C). S can be represented as a function of the CN—a unitless parameter that accounts for various
hydrologic soil groups, land use type or treatment and antecedent soil moisture condition. Land use
types include urban, cultivated agriculture, other agriculture and arid and semiarid rangeland uses. CNs
range from 0 to 100; with higher CNs corresponding to increased runoff. The CN method was developed
for a single event but can be scaled to determine annual average runoff.

The CN method can be used to estimate reductions in runoff resulting from changes in land use and soil
conditions from different agricultural NBS such as cover crops, grass buffers and riparian buffers.
Additionally, the CN method can estimate the annual runoff volume generated from a particular land
use cover and available for groundwater recharge and potential managed aquifer recharge. Practices
often used for managed aquifer recharge include infiltration basins, infiltration trenches, porous
pavement, bioretention and dry wells. This method can be applied at the regional scale (state, county or
watershed level) and at the site level. The EPA's Enhanced Aquifer Recharge of Stormwater in the United
States: State of the Science Review synthesizes current scientific and technical literature surrounding
managed aquifer recharge (EPA 2021). Table 4-2 in the report summarizes recharge volumes and
infiltration rates from case studies across the United States. Managed aquifer recharge can pose risks to
groundwater; appropriate site characterization and data collection is needed to determine the feasibility
of a project.

EPA's Pollutant Load Estimation Tool (PLET) uses the CN method to estimate runoff volume prevented

for protection-based NBS. The runoff volume prevented approach determines the difference in runoff
volumes between an existing land use scenario (such as a forested land use) and a potential future land
use scenario (such as conversion to urban land use). PLET also uses a runoff volume reduction method
to estimate the volume of runoff captured by specific urban BMPs designated with "LID" for low impact
development. Practices include cisterns, rain barrels, bioretention, dry wells, buffer strips, infiltration
swales, infiltration trenches, vegetated swales and wet swales. This method considers the storage
capacity of the BMP, the BMP drainage area (DA, acres), the design runoff depth to be captured by the
BMP (RD, in.) and the runoff volume per storm event (P, in.) to determine an annual runoff volume
reduction (Equations 4-6 in Appendix C).

InVEST's Urban Stormwater Retention model estimates urban runoff retention and potential
groundwater recharge in response to annual precipitation for different land use types. NBS relevant to
the model would include existing or planned natural land covers such as urban tree canopy or parks.
Required model inputs include runoff coefficients, percolation coefficients and a raster of land use and
landcover types. The Urban Stormwater Retention section of the InVEST user guide provides more
details on the methodology.

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i-Tree includes a suite of web-based and desktop tools developed to quantify the benefits of trees for a
variety of user applications (Nowak 2021). The flagship tool, i-Tree Eco, contains all the detailed science
and data inputs; in general, other i-Tree tools discussed here are simplified and faster versions of i-Tree
Eco and apply multipliers determined from i-Tree Eco runs. Across the i-Tree suite, benefits quantified
include water quantity, carbon, air quality and energy savings. Environmental benefits relevant to the
scope of this compendium are highlighted for select i-Tree tools. Users are encouraged to explore the
variety of i-Tree tools beyond what is highlighted here.

• i-Tree Canopy is a web-based tool used to assess the benefits of existing tree canopy cover.
I-Tree canopy uses Google aerial imagery and a standard statistical point survey approach to
determine cover types, such as tree cover, impervious, grass/shrub and so forth. The tool also
includes a change analysis functionality that enables users to evaluate changes over time.
Rainfall interception and avoided runoff are determined based on local weather data and a
standardized volumetric removal rate based on the area of canopy cover (i.e., cubic meters per
square meter, m3/m2).

• i-Tree Planting Calculator is a web-based tool commonly used to estimate the benefits of tree
planting projects for numerous species. The input data requirements include information
specific to the tree species type and diameter at breast height, distance of tree plantings from
buildings, mortality rate and the project lifespan. Estimates for runoff reductions and rainfall
interception use the same methodology as i-Tree Canopy, but results are reported for the
project duration.

EPA's National Stormwater Calculator is a screening-level tool used to compute site hydrology (12 acres
or less) under various land use scenarios. Users can determine runoff volume reduction for specific LID
controls, including disconnection, rain harvesting, rain gardens, green roofs, street planters, infiltration
basins and permeable pavement. Site hydrology is computed in the background using EPA's Storm
Water Management Model (SWMM). The tool provides regionally adjusted capital and operations and
maintenance costs and enables users to consider climate change scenarios for internationally
recognized climate change projections.

Green Roof Energy Calculator is an online tool that estimates and compares the energy performance,
heat flux, evapotranspiration and stormwater runoff volume reductions between a conventional roof
and a green roof. The tool can be used for new and old residential and office buildings. The input data
includes annual precipitation data for 100 cities in the United States and Canada. Runoff volume
reductions are determined based on the user's inputs for the roof surface area, coverage of the green
roof and soil media depth.

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Climate Mitigation Benefits

"Climate mitigation" refers to interventions and actions that reduce greenhouse gas (GHG) emissions
and protect or enhance carbon storage. Protection of forests and many vegetative agricultural NBS
implemented by the Section 319 Program and the Gulf Hypoxia Program provide climate mitigation
benefits. Table 3 lists eight tools to estimate emission reductions, carbon sequestration or carbon
storage.

Climate mitigation-related benefits considered here include the following:

: Emission reductions, which refers to interventions and actions that reduce GHGs (carbon dioxide

[C02], nitrous oxide [N20] and methane [CH4]) emitted into the atmosphere. In the context of
agricultural conservation practices, emission reductions may result from changes in fertilizer
management or biomass burning.3

Carbon sequestration (sometimes referred to as biological carbon sequestration), which refers

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to the natural uptake of C02 from the atmosphere by grasses, shrubs, trees and crops through

the process of photosynthesis. Carbon sequestration is represented as a rate (mass per time).4
C02 Carbon storage, which refers to the total carbon currently stored in vegetation or soil.5

3 Icon made by inipagistudio from www.flaticon.com.

4 Icon made by Freepik from www.flaticon.com.

5 Icon made by Smashicons from www.flaticon.com.

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Table 3. Climate mitigation-related benefits and estimation tools

Tool/Metric

Lead Agency/Org.

Applicable NBS

Benefit

Units

Scale

COMET-Planner

USDA and CSU

Agriculture conservation
practices,

pastureland conservation
practices

ro-trtrtrv

Tons ofC02
equivalents
per yearb

County

ALU National GHG

Inventory

Software

CSU,

EPA,

USAID and
USFS

Agricultural and forest
activities

Unknown

National

lnVEST®-Carbon

Natural Capitals
Project, 2024

Agriculture

pastureland

forest

co2

<&JL

itt

SIJ'TJ OTTtf

i
(

Metric tons of
C per pixel per
year

Land parcel

CaRPE Tool

American
Farmland Trust
and USDA
Agricultural
Research Service

Agriculture conservation
practices (6),
pastureland conservation
practices (4)

Tons ofC02
equivalents
per year

Varies (county
to national
scale)

FLR Carbon
Storage Calculator

Winrock
International

Agroforestry, natural
regeneration

co2
¥

Tons ofC02
stored per
year

State

Cool Farm

Cool Farm Alliance

Reduced tillage, nutrient
management, cover
crops, reforestation

Kg C02
equivalents
per year

Field

i-Tree Canopy

USFSand

cooperating

partners3

Protection of existing
tree canopy

fl IBf!

i
I

Storage:
kg C/m2
sequestration:
kg C/yr

Varies (parcel
to watershed)

i-Tree Planting
Calculator

USFSa

Tree-planting projects

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Climate mitigation tools

COMET-Planner is a web-based tool designed for initial planning purposes and provides an estimate of
the potential carbon sequestration and GHG emission reductions of conservation practices at the county
level. Results are reported as C02 equivalents in tons of C02 per year. Practices within COMET-Planner
have an associated emission reduction coefficient for C02, N20 and CH4 that is derived from a sample-
based approach and COMET-Farm model runs. The USDA Natural Resources Conservation Service
provides a list of NBS that may deliver quantifiable reductions in greenhouse gas emission and/or
increase carbon sequestration on the COMET-Planner web page. The COMET-Planner Report provides
detailed information on the quantification methods behind the tool (USDA and CSU 2022).

The Agriculture and Land Use (ALU) National Greenhouse Gas Inventory Software estimates carbon
emissions and removals associated with biomass and soil in addition to N20 emissions (soil and manure)
and CH4 emissions (rice, enteric and manure). Methods stem from the Intergovernmental Panel on
Climate Change. The program can be downloaded from the tool web page.

The InVEST Carbon Storage and Sequestration model is a simple carbon model that estimates the
annual carbon storage for existing land cover and future land cover scenarios. The tool can be used to
assess changes in carbon storage overtime between existing and future land use scenarios and relies on
land cover maps for inputs. The tool was designed to assist decision-makers with natural resource
management. Because the model is map-based, mapping software such as ArcGIS is needed. More
details can be found on the InVEST Carbon page.

CaRPE Tool. or the Carbon Reduction Potential Evaluation Tool, is a web-based tool that couples
emission reduction coefficients from COMET-Planner with cropland and grazing data from the Census of
Agriculture (2012, 2017, or 2022) to estimate GHG reductions at the county, state, regional or national
scale. CaRPE can map current and future GHG reductions from conservation practice adoption. The
visual interface allows users to view results via table and map displays.

FLR Carbon Storage Calculator is a global tool that estimates carbon storage based on the hectares of
annual planted or restored vegetation for the following activities: agroforestry, plantation operations,
natural regeneration and mangrove restoration. Estimates are based on literature-derived bioaccumulation
rates (carbon dioxide, C02, per hectare per year) for the listed activities (Bernal et al. 2018).

Cool Farm Tool Online, developed by Cool Farm Alliance, is a web-based tool that provides GHG
emission estimates for a specific product at the farm scale (Cool Farm Alliance 2024). The tool can
account for reduced tillage, nutrient management, cover crops and tree planting. Unlike other climate
mitigation tools identified in the compendium, Cool Farm accounts for other direct field emissions,
including combustion of diesel and indirect emissions such as transport. Methodologies in the tool
primarily stem from the Intergovernmental Panel on Climate Change (IPCC 2006, 2019).

i-Tree Canopy uses percent tree cover to determine annual estimates of carbon storage using a
nationalized C02 storage rate (7.69 kg/m2). Carbon sequestration is determined using state-specific
sequestration rates (kg C/m2/yr) (Nowak et al. 2013). Refer to the Water Quantity section of this
compendium for more background details on i-Tree Canopy.

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i-Tree Planting Calculator estimates carbon sequestration over the designated lifespan of a tree-
planting project based on species-specific biomass equations. Refer to the Water Quantity section of this
compendium for more background details on i-Tree Planting Calculator.

Air Benefits

This section presents tools for air quality improvements and ambient air temperature reduction
benefits.

Air quality improvements

Increased traffic density in urban centers contributes to air pollution and areas of elevated exposure
alongside roadways and other air pollution sources (e.g., Karner et al. 2010). Air quality benefits
described in this section refer to air quality improvements by trees and other vegetation for gaseous and
particulate-borne pollutants. While the protection or planting of urban tree canopy and other
vegetation can improve air quality, the impact varies from the local to the regional scale. At the local
scale, air quality benefits are complicated by site-specific factors. Refer to the section Local Scale
Considerations for Air Quality Benefits for resources that discuss more about site-specific factors that
influence green stormwater infrastructure (GSI) air quality benefits in urban settings. At the regional
scale, studies demonstrate the reduction of air pollution via leaf surfaces from tree canopy and
vegetation (Janhall 2015; Gallager et al. 2015). Table 4 lists two tools available for estimating air quality
benefits at the regional and county scale.

Table 4. Air quality benefits and estimation tools

Tool

Lead Agency/Org.

Applicable NBS

Benefit

Units

Scale

i-Tree

Planting

Calculator

USFSa

Tree canopy planting

Air quality
improvement

Pounds or
kg/project
lifespan

County,
project level

i-Tree
Canopy

USFSa

Protection or
management of
existing tree canopy

Air quality
improvement

Tons/year

Varies (parcel
to watershed
scale)

Note: kg = kilograms; USFS = U.S. Forest Service.

aThe i-Tree suite of tools is supported by the cooperative agreement between the USDA Forest Service, Davey Tree Expert
Company, The Arbor Day Foundation, Urban and Community Forestry Society, International Society of Arboriculture and Casey
Trees.

Regional scale air quality tools

i-Tree Planting Calculator estimates air pollution reductions for ozone (03), nitrogen dioxide (N02),
sulfur dioxide (S02) and particulate matter less than 2.5 microns (PIVh.s)- Air pollutant reductions are
reported in pounds or kilograms for the total project lifespan specified by the user. Air pollutant removal
values are derived from i-Tree Eco runs using air pollution and weather data at the county level. Refer to
the Water Quantity section of this compendium for more background details on i-Tree Planting
Calculator.

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i-Tree Canopy applies the same methodology as i-Tree Planting Calculator to determine annual air
pollutant reductions of carbon monoxide, N02, 03, S02, PM2.5 and particulate matter less than 10
microns for an area of existing tree cover (Nowak 2021). Refer to the Water Quantity section of this
compendium for more background details on i-Tree Canopy.

Local-scale considerations for air quality benefits

At the local scale, roadside vegetation type and placement influence whether vegetation reduces or
increases air pollution in urban environments. To achieve air pollution benefits, vegetation along
roadways and near other air pollution sources must have full coverage from the ground to the top of the
canopy with low porosity and high leaf-area density. If gaps between the vegetation or areas of high
porosity exist, air pollutants can accumulate within and beyond the canopy, leading to increased local air
pollution levels. In addition, vegetation near air pollution sources needs to be sufficiently tall and thick
to promote air pollution capture and increased wind turbulence to improve local air quality. While tools
are not yet available to quantify the impacts of GSI along roadways and other air pollution sources, the
following resources highlight important characteristics needed to inform design decisions and optimize
air quality benefits:

• Recommendations for Constructing Roadside Vegetation Barriers to Improve Near-Road Air
Quality: This report identifies qualitative characteristics and best practices to improve air quality
when implementing vegetation along roadsides (Baldauf 2016).

• The effects of roadside vegetation characteristics on local, near-road air quality: This review
article provides estimates of air pollution reductions under differing vegetation characteristics
(Deshmukh et al. 2019).

• Air pollution abatement performances of green infrastructure in open road and built-up street
canyon environments - A review: This review focuses on the effect of tree canopy, sedges,
green walls and green roofs on air quality in street canyon and open road settings (Abhijith et al.
2017).

Ambient air temperature reduction

Because of the higher density of buildings and pavement in urban environments, developed settings
absorb and reemit more heat than natural land covers. The release of heat in urban environments
creates pockets of higher temperature on surfaces and in the air referred to as "heat islands." Heat
islands can contribute to compromised human health and increased temperatures of urban runoff,
which can lead to thermal pollution and the degradation of habitat in nearby rivers and streams.
Ambient air temperature reductions refer to temperature reductions provided by trees, vegetation and
green roofs through processes of shading and evapotranspiration (EPA 2008b). Table 5 lists three tools
for estimating ambient air temperature reductions.

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Table 5. Air temperature reduction benefits and estimation tools

Tool

Lead Agency/Org.

Applicable NBS

Benefit

Units

Scale

InVEST-Urban
Cooling

Natural Capital
Project, 2024

Urban green spaces
(i.e., tree canopy and
urban parks) > 2 ha

Urban Heat

Mitigation

Index

Unitless
(0-1)

City

i-Tree Research
suite; Cool Air

USFSa

Tree canopy

Ambient air

temperature

reduction

°F

Varies
(local, city,
regional)

Green Roof

Energy

Calculator

Arizona State
University,
Toronto
University and
Green Roofs for
Healthy Cities

Green roofs

Latent and
sensible heat
flux

W/m2

Building
level

Notes: °F = degrees Fahrenheit; ha = hectares; W/m2 = watts per square meter.

Ambient air temperature reduction tools

InVEST's Urban Cooling model estimates the cooling effect of green spaces (more than 2 hectares in
area) on surrounding land covers using the Heat Mitigation Index (HMI). The HMI is determined based
on the cooling capacity, a function of shade, evapotranspiration and albedo, for each land cover grid cell
in the study area. Cooling capacity is a unitless number ranging from 0 to 1 where "0" represents no
cooling capacity and "1" represents maximum cooling capacity. HMI equals the cooling capacity if the
pixel is unaffected by green space or equals a weighted average of the cooling capacity values along the
distance from the green space to the area of interest. The Urban Cooling section in the InVEST User Guide
provides more detail on the methodology. HMI is displayed on a map. Similar to the InVEST Carbon
Storage and Sequestration model, mapping software such as ArcGIS is needed.

i-Tree Cool Air is a spatial air temperature model that is a component of the i-Tree Research Suite. i-Tree
Cool Air simulates the impact of land use and tree cover on air temperature and humidity. The tool
requires the use of a geographic information system to display outputs and can evaluate air
temperature effects at the local and regional scale.

Green Roof Energy Calculator is an online tool that compares the energy performance, heat flux,
evapotranspiration and stormwater runoff reductions between a conventional roof and a green roof.
The tool can be used for residential and office buildings and includes input data for 100 cities in the
United States and Canada. Latent heat is felt as humidity and is represented in units of watts per square
meter (W/m2). Sensible heat flux describes the temperature difference between the roof surface and
surrounding air and also is represented in units of W/m2. Green roofs result in an increase in latent heat
and a decrease in sensible heat flux, which results in a cooling effect.

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Habitat Benefits

Habitat benefits can be realized when NBS create, protect or restore habitat for wildlife and ecological
function. Quantification of habitat is more nuanced than other environmental benefits previously
described because it can be represented by a variety of indicators or metrics such as a habitat quality
score, vegetation diversity, abundance of wildlife or miles of stream length connected for fish passage.
Table 6 summarizes qualitative tools or metrics to communicate habitat benefits.

Table 6. Habitat related benefits, estimation tools and metrics

Benefit
Tool/Metric

Lead

Agency/Org.

Applicable NBS or
land use types

Units

Scale

Habitat

Potential Index

Field to Market's
Field Print
Platform
(partnered w/
USGS)

Cropland,
pastureland, forest
and wetlands

Unitless
(0-100)

Field/farm
scale

InVEST Habitat
Quality

Natural Capitals
Project, 2024

Protection of
existing natural land
cover

Unitless
(0-1)

Watershed

Beaver
Restoration
Assessment
Tool (BRAT)

Utah State
University

Stream conservation
and restoration

Varies

Watershed
or regional

Database of

biodiversity,

habitat, and

aquatic

resource

quantification

tools

USGS and EPA

Conservation and

compensatory

mitigation

Varies

Habit
protected

N/A

Conservation
easements, land
acquisition wetland
protection

Examples include:

• Acres of wetland
protected

• Acres of open space

Varies

Habitat created

N/A

GSI, cropland and
pastureland NBS

Examples include:

• Acres of greening from
GSI

• Acres of tree canopy

Varies

Aquatic
connectivity

N/A

Dam removal, road
stream crossing
removal or
replacement with
ecological function

Example units include:

• Stream miles connected
for fish passage

• Stream miles of restored
floodplain connection

Varies

Notes'. N/A = not applicable; USGS = United State Geological Survey; GSI = green stormwater infrastructure.

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Habitat assessment tools and metrics

The Habitat Potential Index for Biodiversity provides a qualitative assessment of the effect of
agricultural land use on habitat quality and quantity. Both production and nonproduction lands are
considered. The index ranges from 0 to 100 and is meant to promote protection and/or enhancements
of existing habitat. For example, a score less than 50% indicates more opportunities exist to improve
habitat. More information about the Habitat Potential Index Score can be found in Field to Market's
Harnessing Sustainability Insights & Unleashing Opportunity.

InVEST's Habitat Quality model maps the biodiversity of a landscape by coupling land use data with
threats to biodiversity. The model displays habitat quality scores as a proxy for biodiversity. Habitat
quality is a qualitative unitless number that ranges from 0 to 1 where "0" indicates poor habitat
suitability and "1" indicates high habitat suitability. The habitat quality score is a function of several
factors that include the relative impact of each threat, the impact across the distance between the
threat and the habitat, whether the habitat is protected from disturbance, and the sensitivity of habitat
type to threats on the landscape. The model can be used to evaluate the impact of different land use
changes or management scenarios on biodiversity relative to a baseline.

Beaver Restoration Assessment Tool (BRAT) is a planning-level tool that consists of spatial models to
predict the potential for beaver dam building activity. BRAT can be used at the watershed or regional
scale. Outputs of the tool provide information for each stream segment, including beaver dam capacity
(units of dams per kilometer or mile) and estimated beaver dam complex or the maximum number of
beaver dams. The tool also provides management information such as habitat limitations to beaver
dams, undesirable beaver dam locations and beaver dam opportunities.

Database of biodiversity, habitat, and aquatic-resource quantification tools used in market-based
conservation in the United States summarizes attributes of 107 quantification tools developed for
market-based conservation, non-compensatory mitigation, and voluntary conservation and restoration
programs within the United States (Chiavacci et al. 2022). The database is presented in a downloadable
spreadsheet format and describes 33 different attributes, including locations of use, user skill level, focal
habitat, data inputs and output types.

Habitat created refers to restoration NBS that add, create or extend natural ecosystems to increase
biodiversity. Habitat created can be reported as a unit area of land cover.

Habitat protection refers to protection interventions that protect and prevent the loss of natural
ecosystems from future development or land disturbance. Similar to habitat created, habitat protected
can be reported as a unit area of land cover.

Aquatic connectivity is defined by the U.S. Fish and Wildlife Service as physically linked pathways
through which energy, matter and organisms move from one place to another through water. It includes
longitudinal connectivity upstream and downstream and vertical movement within a water column as
well as lateral connectivity of the main waterbody to riparian and floodplain habitat, all of which play a
vital role in a functioning aquatic ecosystem (USFWS 2021). Aquatic connectivity can be reported using a
variety of metrics such as stream length opened for aquatic passage or stream length with floodplain
connectivity.

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Conclusion

This compendium connects NBS to environmental benefits and associated estimation methods or tools
related to water quantity, climate mitigation, air and habitat. Readers can use this resource to estimate
environmental benefits for activities such as:

• Preparing watershed-based plans;

• Writing grant proposals;

• Screening NBS;

• Communicating the benefits of NBS; and

• Evaluating or informing management actions or decisions.

Depending on the NBS and their scale, estimating multiple environmental benefits may necessitate the
use of more than one tool. For example, i-Tree and InVEST estimate environmental benefits in more
than one benefit category whereas COMET-Planner is specific to climate mitigation benefits only.
Additionally, when summarizing multiple environmental benefits for the activities mentioned above,
users of this compendium should pay attention to the various units across benefit categories and tools
(Tables 2-5). For example, units may vary by the quantification metric for a benefit category (e.g.,
million gallons per square miles per year [Mgal/mi2/year] versus cubic meters per year [m3/year] for
runoff retention) or by time (e.g., benefits quantified for a year versus a project lifespan).

The EPA intends to update this document periodically to incorporate tool enhancements and add new
tools and other resources as they are developed. Many of the tool web pages identified in the
compendium provide training videos and other support materials. Additionally, American Farmland
Trust organized an Outcomes Estimation Tools Training Webinar Series that includes some tools
described here including COMET-Planner and Cool Farm.

References

Abhijith, K.V., Kumar, P., Gallagher, J., McNabola, A., Baldauf, R., Pilla, F., Broderick, B., Di Sabatino, S.,
and Pulvirenti, B. 2017. Air pollution abatement performances of green infrastructure in open road and
built-up street canyon environments - A review. Atmospheric Environment 162: 71-86. ISSN 1352-2310.
https://doi.Org/10.1016/i.atmosenv.2017.05.014.

Baldauf, R. 2016. Recommendations for Constructing Roadside Vegetation Barriers to Improve Near-
Road Air Quality. EPA/600/R-16/072. U.S. Environmental Protection Agency, Washington, DC.

Bernal, B., Murry, L.T., and Pearon, T. 2018. Global Carbon dioxide removal rates from forest landscape
restoration activities. Carbon Balance and Management Accessed April 2024.
https://doi.org/10.1186/sl3021-018-011Q-8.

Chiavacci, S.J., French, E.D., and Morgan, J.A. 2022. Database of Biodiversity, Habitat, and Aquatic
Resource Quantification Tools Used for Market-based Conservation in the United States. Version 2.0,
June 2022. U.S. Geological Survey. https://doi.org/10.5066/F79G5M3X.

Cool Farm Alliance. 2024. Cool Farm Tool and Platform - Technical Method Description - version CFT
XXX. Tool and description available at https://coolfarmtool.org/.

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Deshmukh, P., Isakov, V., Venkatram, A., Yang, B., Xhang, M., Logan R., and Baldauf, R. 2019. The effects
of roadside vegetation characteristics on local, near-road air quality. Air Quality, Atmosphere & Health
12:259-270. https://doi.org/10.1007/sll869-018-Q651-8.

EPA (U.S. Environmental Protection Agency). 2008a. Handbook for Developing Watershed Plans to
Restore and Protect our Water.

https://www.epa.gov/nps/handbook-developing-watershed-plans-restore-and-protect-our-waters.

EPA. 2008b. Reducing Urban Heat Islands: Compendium of Strategies. Accessed March 2024.
https://www.epa.gov/heatislands/heat-island-compendium.

EPA. 2021. Enhanced Aquifer Recharge of Stormwater in the United States: State of the Science Review.
Accessed April 2024.

https://cfpub.epa.gov/si/si public record Report.cfm?dirEntryld=352238&Lab=CPHEA.

EPA. 2022. User Guide Pollutant Load Estimation Tool Version 1.0. Accessed April 2024.
https://www.epa.gov/svstem/files/documents/2022-04/user-guide-final-04-18-22 508.pdf.

EPA. 2023. Green Infrastructure Modeling Toolkit. Accessed May 2024.
https://www.epa.gov/water-research/green-infrastructure-modeling-toolkit.

Gallagher, J., Baldauf, R., Fuller, C.H., Kumar, P., Gill, L.W., and McNabola, A. 2015. Passive methods for
improving air quality in the built environment: A review of porous and solid barriers. Atmospheric
Environment 120(2015): 61-70. https://doi.Org/10.1016/i.atmosenv.2015.08.075.

IPCC (Intergovernmental Panel on Climate Change). 2006. IPCC Guidelines for National Greenhouse
Gas Inventories. Prepared by The National Greenhouse Gas Inventories Programme. Technical Report.
Accessed May 2024.

https://www.ipcc.ch/report/2006-ipcc-guidelines-for-national-greenhouse-gas-inventories/.

IPCC. 2019. 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories.
Technical Report. Accessed May 2024. https://www.ipcc.ch/report/2019-refinement-to-the-2006-ipcc-
guidelines-for-national-greenhouse-gas-inventories/.

Janhall, S. 2015. Review on urban vegetation and particle air pollution - Deposition and dispersion.
Atmospheric Environment 105(2015): 130-137. https://doi.Org/10.1016/i.atmosenv.2015.01.052.

Karner, A., Eisinger, D.S., and Niemeier, D.A. 2010. Near roadway air quality: Synthesizing the finding
from real-world data. Environmental Science & Technology 44(14): 5334-5344. DOI: 10.1021/esl00008x.

Nowak, D.J. 2021. Understanding i-Tree: 2021 Summary of Program and Methods. Accessed April 2024.
https://www.itreetools.org/documents/650/i-Tree Methods gtr nrs200-2021.pdf.

Nowak, D.J., Greenfield, E.J., Hoehn, R.R., and Lapoint, E. 2013. Carbon storage and sequestration by
trees in urban and community areas of the United States. Environmental Pollution. Accessed April 2024.
https://www.itreetools.org/documents/64/nrs 2013 nowak 001.pdf.

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USDA and CSU (U.S. Department of Agriculture and Colorado State University). 2022. COMET-Planner
Carbon and Greenhouse Gas Evaluation for NRCS Conservation Practice Planning. Accessed May 2024.
https://storage.googleapis.com/comet public directory/planner50states/pdfs/COMET-
PlannerReport.pdf.

USDA (United States Department of Agriculture). 2004. Part 630 Hydrology National Engineering
Handbook. Accessed September 2024.

https://irrigationtoolbox.com/NEH/Part630 Hydrology/H 210 630 09.pdf

USFWS (U.S. Fish and Wildlife Service). 2021. Evaluation of Aquatic Connectivity and Fish Passage for
Service Actions. Accessed April 2024. https://www.fws.gov/policy-librarv/710fw2.

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Appendix A: Restoration versus Protection Actions

Table A.l Distinction between restoration and protection NBS intervention.

Table developed by EPA 2024

Intervention
Type

As Defined with respect to Waterbodv
Condition

As Defined with respect to Best
Management Practices or NBS

Protection

Waterbodies that continue to meet
water quality standards for one or
more pollutants and/or designated
uses.

Management actions specifically
implemented to preserve existing natural
lands to prevent future pollutant loading
to waterbodies, such as:

• Land conservation;

• Wetland protection; and

• Riparian area protection.

Restoration

Waterbodies that meet water quality
standards for one or more pollutants
and/or designated uses after being
previously included on the Clean Water
Act Section 303(d) list of impaired
waters.

Management actions implemented to
reduce existing pollutant loading to
waterbodies, such as:

• Green stormwater infrastructure;

• Conservation tillage; and

• Floodplain restoration

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Appendix B: Literature Review - Systematic Abstract Screening

The EPA conducted a systematic abstract screening of peer-reviewed literature for urban-related nature-
based solutions (NBS). The primary objectives of the abstract screening included (1) to assess the most
frequently reported environmental benefits and (2) to screen methods to monitor or quantify
environmental benefits.

This appendix summarizes the methodology and results of the screening. A total of 478 abstracts were
collected and analyzed based on the inclusion criteria described in the following Methodology section. In
summary, field and modeling studies were the top two study categories. For modeling studies, abstract
screening identified various methods for quantifying environmental benefits. While most of the studies
pointed to complex models (i.e., high data input requirements and best used for design and NBS sizing),
studies also used simpler tools (i.e., low input data requirements and best used for the screening and
planning level) such as InVEST and the i-Tree suite of tools. Findings from the systematic abstract
screening informed the expansion of the literature search to include white papers, government web
pages and other resources to identify simple and publicly available tools.

Methodology

The literature pull for the systematic abstract screening was conducted in Web of Science. Colandr, an
open-source literature screening platform, was used to screen abstracts. Articles were included that met
the following criteria:

• The article had to pertain to one of the following NBS: bioretention, green roof, permeable
pavement, tree trenches, vegetated swale, rainwater harvesting, tree canopy, floodplain
restoration, riparian buffers, constructed wetland, green wall, grassed waterway or sediment
basin

• The study had to measure or quantify one or more of the following environmental benefits:
flood mitigation, event flow reduction, evapotranspiration, groundwater recharge, thermal
pollution mitigation, heat island mitigation, erosion control, water reuse, runoff retention,
pollutant removal, climate change adaptation, recreational space, improved air quality,
ecological flow or biodiversity

Included articles were documented in a spreadsheet based on the screening tags noted below. The
spreadsheet is available from the EPA upon request. Power Bl was used to visualize results.

Search Strings

The following search strings were used in Web of Science Core Collection on February 24, 2022, and
April 5, 2022, which resulted in a return of 2,964 articles. Meta data for the articles were imported into
Colandr, where 429 duplicates were removed for a total of 2,535 articles.

• Search string NBS type, co-benefit, and evaluation (February 24, 2022)
returns = 1,557

(TS=("bioretention" OR "rain garden" OR "permeable pavement" or "green roof" OR "tree
trench" or "vegetated swale" or "rainwater harvesting" or "tree canopy" or "green wall" or
"sediment basin" or "grassed waterway" or "constructed wetland" or "wetland" or "floodplain
restoration" or "riparian buffers")) AND (TS=("co-benefits" or "benefits" or "ecosystem
services")) AND (TS=("evaluation" or "framework" or "assessment" or "monitoring"))

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• Search string NBStype, co-benefit, and climate change (February 24. 2022)

Returns = 879

(TS=("bioretention" OR "rain garden" OR "permeable pavement" or "green roof" OR "tree
trench" or "vegetated swale" or "rainwater harvesting" or "tree canopy" or "green wall" or
"sediment basin" or "grassed waterway" or "constructed wetland" or "wetland" or "floodplain
restoration" or "riparian buffers" )) AND (TS=("co-benefits" or "benefits" or "ecosystem
services")) AND (TS=("climate change" or "climate adaption" or "resilience" or "climate
mitigation"))

• Expanded search for bioretention and permeable pavement using the keywords noted below
(April 5. 2022)

Returns = 528

(ALL=("bioretention" OR "biofiltration" OR porous pavement OR pervious concrete OR
"bioswale" OR "grassed swale" OR "tree pit")) AND ALL=("co-benefits" OR "benefits" OR
"ecosystem services" OR "climate change" OR "climate adaption" OR "resilience" OR "climate
mitigation")

Screening Tags

Included articles were documented in a spreadsheet using the following screening tags.

Country:

• US; state

• not US; country

Nature-Based Solutions:

• bioretention/rain garden

• green roof

• permeable pavement

• tree trenches

• vegetated swale

• rainwater harvesting

• tree canopy/urban trees

• green wall

• grassed waterway

• sediment basin

• floodplain restoration

• riparian buffers

• constructed wetland

Study Type:

• field

• laboratory

• modeling

• case study

• review

Environmental Benefit:

• flood mitigation

• event flow reduction

• pollutant removal

• evapotranspiration

• groundwater recharge

• thermal pollution mitigation

• heat island mitigation

• water reuse

• runoff retention

• climate change adaption

• improved air quality

• ecological flow (base flow)

• biodiversity

• carbon sequestration

• dis-services/failures

Assessment Tool:

• monitoring

• modeling

• monitoring and modeling

• life cycle assessment

• cost/benefit analysis

• metanalysis

• evaluation framework

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Results

The EPA screened 76 percent of the 2,535 pulled abstracts. A total of 478 abstracts were included. Table
B.l shows a heat map of the count of articles that quantified specific environmental benefits for the
most frequently reported NBS in the included abstracts. Green roofs, bioretention, constructed
wetlands, permeable pavement and NBS treatment trains were the most studied types of NBS. "NBS
treatment trains" refers to more than one NBS solution in series. The "Other" column represents all
other NBS types considered (see the nature-based solutions screening tags on the previous page).

Table B.l Heat map of NBS and reported benefits for systematic abstract screening.

Darker shades of green correspond to higher article counts.

NBS

Green Constructed Permeable treatment

BMP Practice (groups)

Bioretention

roof

wetland

pavement train

Other

Carbon sequestration

Climate change adaption

Ecological flow (base flow)

Erosion control

Evapotranspiration

Event flow reduction

Flood mitigation

Groundwater recharge

Habitat/biodiversity

Heat island mitigation

Improved air quality

Pollutant removal

Recreational space

Runoff retention

Trade-offs

Water reuse

Field and modeling studies were the top two study categories. For field studies, monitoring was the
predominant assessment method. For modeling studies, EPA SWMM and Soil and Water Assessment
Tool (SWAT) were the predominant assessment tools. Abstracts documented the use of both models to
quantify flood mitigation, runoff retention, event flow reduction, groundwater recharge, water reuse,
pollutant removal, climate change adaptation and trade-offs. In addition to these advanced models,
abstracts also reported the use of simple tools such as InVEST, i-Tree Eco and i-Tree canopy.

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Appendix C: Referenced Equations

Curve Number

Runoff amount (Q in., Equation 1) is estimated as a function of rainfall depth (P, in.), potential maximum
retention after runoff begins (S, in.) and initial abstraction (la, in, Equation 2). S can be represented as a
function of the curve number (CN)—a unitless parameter that accounts for various hydrologic soil
groups and land use types including urban, cultivated agriculture, other agriculture, and arid and
semiarid rangeland uses (Equation 3).

Q = (P~'af Eq. 1

v (P-ia)+s

where:

Ia = 0.2S Eq. 2

C 1000 1(1 I- o

S = 10 Eq. 3

CN ^

The Runoff Reduction Methods

This method considers the storage capacity of the BMP, the BMP drainage area (DA, acres), the percent
imperviousness within the drainage area (PI, %), the design runoff depth to be captured by the BMP (RD,
in.), and the runoff volume per storm event (P, in.) to determine an annual runoff volume reduction
(Equations 4-6). Refer to the Model Documentation section the PLET web page for more details.

BMPstorage (ac - ft) = DA* PI * — Eq. 4

Runoffvot (ac — ft) = DA * PI * ^ Eq. 5

Runoffred = minimum (BMPstorage, Runoffvoi) Eq. 6

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