ADAPTING TO CLIMATE CHANGE
SOUTHWEST
The Southwest is the hottest and driest region in the U.S., already parched and facing
climate change challenges. Its northern half is expected to get hotter, its southern half,
significantly drier. Projected higher temperatures in most areas, increased precipitation,
and more frequent and intense storms in others, pose challenges to communities as they
protect water infrastructure, maintain air quality, and protect streamflows and wetlands.
Many communities are building resilience to the risks they face under current climatic
conditions. This fact sheet provides examples of communities that are going beyond
resilience to anticipate and prepare for future impacts.
Observed and Projected Changes in the Southwest
Intense storms have decreased
Observed Change in Very Heavy Precipitation
Average Annual
Temperature
Observed Temperature
&EPA
stales
Environmental Protection
Agency
Moving Beyond Resilience to Adaptation
Climate change adaptation goes
beyond resilience by taking actions to
address future risks. Adaptation refers
to how communities anticipate, plan,
and prepare for a changing climate.
Average Annual
Temperature Increases
Projected Temperature
The Southwest experienced a 5% increase
in the amount of precipitation falling in
very heavy events (the heaviest 1%) from
1958 to 2012.
This map shows the average annual
temperature (°F) from 1981 to 2010 in the
Southwest.
The Southwest is expected to experience an
increase in the average annual temperature
(°F) from 2041 to 2070 compared to 1971 to
1999 under a high emissions scenario.
Protecting Water Infrastructure
Future projections for less total annual rainfall, less snowpack in the mountains, and earlier snowmelt mean that less water will
likely be available during the summer months when demand is highest. This will make it more difficult for water managers in the
Southwest to satisfy water demands throughout the course of the year. Freshwater resources along the California coast,
however, face risks from climate-induced drought and sea level rise. As sea levels rise more quickly, saltwater moves into
freshwater areas. This may force water managers to seek other sources of fresh water. Key vulnerabilities include:
• More frequent and intense storms may overwhelm operations and service capacity of water and wastewater systems, which
could threaten drinking water availability, and lead to more sewer system overflows.
• Flooding and storms may cause the release of contaminants from Corrective Action sites, Superfund sites, brownfield sites
and landfills.
• Sea level rise and storm surge may submerge and damage critical facilities.
Adaptation in Action
Southern Nevada Water Authority (SNWA) - a cooperative of seven drinking water and wastewater agencies - serves more than
two million residents in Nevada, including the city of Las Vegas. SNWA worked with EPA's Climate Ready Water Utilities program
to conduct a vulnerability assessment of the Las Vegas service area that considered climate change impacts and vulnerabilities in
in 2035 and in 2060. Projected climate impacts included hotter and drier summers, drought conditions, and increased algal
blooms. SNWA followed this initial analysis with more in-depth assessments of water source availability under future climate
change, population increase, and water demand projections. These later assessments provided SNWA with a better
understanding of its climate risks and potential vulnerabilities, and enabled them to begin to adapt. SNWA continues to adapt as
a member of the Water Utility Climate Alliance, a consortium of ten of the largest water providers around the country, actively
engaged on climate change adaptation.
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ADAPTING TO CLIMATE CHANGE
SOUTHWEST
Maintaining Air Quality
Increased warming and drought caused by or linked to climate change have increased wildfires and impacts to people and
ecosystems in the Southwest. Fire models project more wildfire and increased risks to communities. High temperatures
associated with climate change are also contributing to the formation of ground-level ozone, which poses a risk to people with
asthma and other respiratory illnesses. Ground-level ozone is projected to increase, causing more heart and lung disease and
deaths. Key vulnerabilities include:
• Climate change can exacerbate peak ozone concentrations on days where weather already contributes to high ozone
concentrations, e.g., days with warmer or stagnant air.
• Climate change can lengthen the ozone season, which typically occurs during the summer, which is also prime wildfire season.
• Higher temperatures from climate change are projected to increase the frequency and severity of wildfires.
Adaptation in Action
Wildfires are an obvious threat to property and public safety, and they can also significantly affect air quality by increasing the
amount of particulates in the air. Because of this, California included wildfire threats within its 2009 Climate Adaptation Strategy
and seeks to reduce the risk of wildfires occurring in the future and reduce the vulnerability of people to wildfires. The state
conducted a vulnerability assessment to better understand the projected impact climate change could have on wildfire activity,
including concerns such as the effectiveness of California's climate sinks (i.e., carbon stored in vegetation) and how projected
climate changes are expected to impact them. California's 2010 Rangeland Assessment's chapter on climate change notes that
the fire season has been starting sooner and ending later, and the severity of wildfire acreage burned has been increasing in
recent years. California is addressing the risk that more wildfires will occur under a changing climate by improving land use
planning by avoiding future development in high fire hazard areas, implementing fire safe practices around homes, and using
ignition-resistant construction.
Protecting Streamflows and Wetlands
Winter snowpack, which slowly melts and releases water in spring and summer, when both natural ecosystems and people have
the greatest needs for water, is key to the Southwest's hydrology and water supplies. Over the past 50 years, there has been less
late-winter precipitation falling as snow, earlier snowmelt, and earlier arrival of most of the year's streamflow. Recent
streamflows in the four major drainage basins of the Southwest have been lower than their twentieth century averages.
Streamflow totals in the Sacramento-San Joaquin Rivers, Upper Colorado, Rio Grande, and Great Basin were 5% to 37% lower
during 2001-2010 than their twentieth century average flows. Moreover, streamflow and snowmelt in many snowmelt-fed
streams of the Southwest tended to arrive earlier in the year during the late twentieth century than earlier in the twentieth
century. Key vulnerabilities include:
• When combined with higher temperatures due to climate change, the decrease of water draining from the landscape into
rivers and reservoirs typically can be double or triple the proportional reductions in rainfall amounts.
• Reduced amounts of rainfall affect the functioning of inland and coastal wetlands, which filter water and help reduce flooding.
Adaptation in Action
Regional water purveyors in the Los Osos Basin in California worked together with the Morro Bay National Estuary Program to
better identify climate change threats from saltwater intrusion and alterations to the groundwater recharge cycle. EPA facilitated
this exercise by using the Climate Resilience Evaluation and Awareness Tool (GREAT) framework to identify climate change threats
and vulnerable assets, and to evaluate adaptation options throughout the Los Osos Groundwater Basin. With help from EPA, local
water purveyors and the estuary program were able to identify potentially vulnerable assets and address potential vulnerabilities.
This partnership and collaborative research allowed both stakeholders to gain valuable insights about water resource
management in the Los Osos Basin, and to inform the current and ongoing development of the Los Osos Groundwater Basin
Management Plan. These stakeholders are continuing their work to ensure that the adaptation options identified will be effective
in dealing with the expected impacts of climate change.
For a comprehensive view of projected climate changes in your region, consult:
.sessment
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JUNE 2016
OFFICE OF POLICY
EPA-230-F-16-017
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