Water Resources Impacts & Adaptation

Climate Impacts on Water

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Observed drought trends in the United States, with hatching indicating a significant trend. Source: USGCRP (2009)

Water resources are important to both society and ecosystems. We depend on a reliable, clean supply of drinking water to sustain our health. We also need water for agriculture, energy production, navigation, recreation, and manufacturing.

Many of these uses put pressure on water resources, stresses that are likely to be exacerbated by climate change. In many areas, climate change is likely to increase water demand while shrinking water supplies. This shifting balance would challenge water managers to simultaneously meet the needs of growing communities, sensitive ecosystems, farmers, ranchers, energy producers, and manufacturers.

In some areas, water shortages will be less of a problem than increases in runoff, flooding, or sea level rise. These effects can reduce the quality of water and can damage the infrastructure that we use to transport and deliver water.

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Impacts on Water Cycle and Water Demand

The water cycle (shown in the following figure) is a delicate balance of precipitation, evaporation, and all of the steps in between. Warmer temperatures increase the rate of evaporation of water into the atmosphere, in effect increasing the atmosphere's capacity to "hold" water. ^[1] Increased evaporation may dry out some areas and fall as excess precipitation on other areas.

Changes in the amount of rain falling during storms provide evidence that the water cycle is already changing. Over the past 50 years, the amount of rain falling during the most intense 1% of storms increased by almost 20%. ^[1] Warming winter temperatures cause more precipitation to fall as rain rather than snow. Furthermore, rising temperatures cause snow to begin melting earlier in the year. This alters the timing of streamflow in rivers that have their sources in mountainous areas. ^[1]

As temperatures rise, people and animals need more water to maintain their health and thrive. Many important economic activities, like producing energy at power plants, raising livestock, and growing food crops, also require water. The amount of water available for these activities may be reduced as Earth warms, and if competition for water resources increases. ^[1]

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Projected changes in the water cycle.
Source: USGCRP (2009)

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Impacts on Water Supply

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Matching photographs taken 18 months apart during the most serious period of recent drought show a significant decrease in Lake Powell. Source: USGCRP (2009)

Many areas of the United States, especially the West, currently face water supply issues. The amount of water available in these areas is already limited, and demand will continue to rise as population grows. The West has experienced less rain over the past 50 years, as well as increases in the severity and length of droughts; this has been especially of concern in the Southwest. ^[1]

In the western part of the United States, 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 to satisfy water demands throughout the course of the year. ^{[2] [3]}

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Impacts on Water Quality

Lake Superior summer air and water temperatures (1979-2006): the recent large jump in summer water temperature is related to the recent large reduction in ice cover. Source: USGCRP (2009)

Heavy rain in 2004 damaged the city water system in Asheville, North Carolina. Source: USGCRP (2009) (PDF)

Coastal Water Supply ^{[1] [3] [4] [5] [6]}

The quality of water supply in coastal and island regions is at risk from rising sea level and changes in precipitation. Rising sea level and the occurrence of drought can increase the salinity of both surface water and ground water through salt water intrusion.

For example, the freshwater Everglades currently recharge Florida's Biscayne aquifer, a natural underground area that collects water and is the primary water supply to the Florida Keys. If rising sea levels submerge low-lying areas of the Everglades, portions of the aquifer would become saline. Sea level rise can also push salty water upstream in coastal areas, threatening surface water supplies. Aquifers in New Jersey east of Philadelphia are recharged by fresh portions of the Delaware River, which become saline during severe droughts.

Freshwater resources on some islands, especially small islands and atolls, can be limited, as supply depends on shallow aquifers, which are recharged by precipitation. These freshwater lenses float on top of the saltwater, and rising sea level diminishes the area above sea level in which the lens can reside. (For more detailed information,see the illustration on page 158 of this Climate Change Science Program Report (PDF)). Sea level rise can turn these shallow aquifers brackish through saltwater intrusion and droughts reduce the water available from other sources, further stressing these limited water supplies.

The Biscayne Aquifer provides almost all of the freshwater for the Keys, Miami, and the lower East Coast of Florida. Although a small part of the aquifer is beneath salty mangrove area, most of it is recharged by the freshwater Everglades. As sea level rises, saltwater will invade part of the Everglades, threatening both that ecosystem and the aquifer that lies beneath it.
Source: EPA (2002)

Water quality could suffer in areas experiencing increases in rainfall. For example, in the Northeast and Midwest increases in heavy precipitation events could cause problems for the water infrastructure, as sewer systems and water treatment plants are overwhelmed by the increased volumes of water. ^[1] Heavy downpours can increase the amount of runoff into rivers and lakes, washing sediment, nutrients, pollutants, trash, animal waste, and other materials into water supplies, making them unusable, unsafe, or in need of water treatment. ^[2] For information about how climate change and water quality affect public health, visit the Health Impacts & Adaptation page.

Freshwater resources along the coasts face risks from sea level rise. As the sea rises, saltwater moves into freshwater areas. This may force water managers to seek other sources of fresh water, or increase the need for desalination (or removal of salt from the water) for some coastal freshwater aquifers used as drinking water supply. ^[1] In addition, as more freshwater is removed from rivers for human use, saltwater will move farther upstream. Drought can cause coastal water resources to become more saline as freshwater supplies from rivers are reduced. Water infrastructure in coastal cities, including sewer systems and wastewater treatment facilities, faces risks from rising sea levels and the damaging impacts of storm surges. ^[2]

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Impacts of Changes in Water Resources on Other Sectors

Warming air temperature can directly raise stream and lake temperatures, which can harm aquatic organisms that live in coldwater habitats, such as trout. Additionally, warmer water can increase the range of non-native fish species, permitting them to move into previously coldwater streams. The population of native fish species often decreases as non-native fish prey on and out-compete them for food. ^[2] For more information about how water quality impacts ecosystems, visit the Ecosystem Impacts & Adaptation page.

The impacts of climate change on water availability and water quality will affect many sectors, including energy production, infrastructure, human health, agriculture, and ecosystems.

Some regions of the United States, particularly the Northwest, use water to produce energy through hydropower. If climate change results in lower streamflows in areas where hydropower is generated, it will reduce the amount of energy that can be produced. Changes in the timing of streamflow can also have an impact on the ability to produce hydroelectricity. Lower water flows would also reduce the amount of water available to cool fossil-fuel and nuclear power plants. To learn more about climate change impacts on energy production, visit the Energy Impacts & Adaptation page.

Climate change impacts on water supply and quality will also affect tourism and recreation. The quality of lakes, streams, coastal beaches, and other water bodies that are used for swimming, fishing, and other recreational activities can be affected by changes in precipitation, increases in temperature, and sea level rise. In addition, winter sport activities that depend on the production of snow and ice could be limited in the future as temperatures increase. ^[1] For more information about how climate change may impact tourism and recreation, visit the Society Impacts & Adaptation page.

Agriculture and livestock depend on water. Heavy rainfall and flooding can damage crops and increase soil erosion and delay planting. Additionally, areas that experience more frequent droughts will have less water available for crops and livestock. To learn more about how climate change will impact agriculture and food production, visit the Agriculture and Food Supply Impacts page. ^[1]

Aquatic species that live in only coldwater environments, such as salmon, will be affected by rising water temperatures. Changing water temperatures would also affect the geographic range of fish species. ^[1]

Changes in the availability and quality of water are also major concerns for other countries where water resources are already stressed. For more information on these issues, please see the International Impacts & Adaptation page.

Planners across many sectors will confront the challenge of a changing water supply. They will likely adopt a variety of adaptation practices, designed to better conserve our water supplies, improve water recycling, and develop alternative strategies for water management. For more information, please visit the Water Resources Adaptation section.

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References

1. USGCRP (2009). Global Climate Change Impacts in the United States . Karl, T.R. J.M. Melillo, and T.C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.

2. CCSP (2008). The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States . A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Backlund, P., A. Janetos, D. Schimel, J. Hatfield, K. Boote, P. Fay, L. Hahn, C. Izaurralde, B.A. Kimball, T. Mader, J. Morgan, D. Ort, W. Polley, A. Thomson, D. Wolfe, M. Ryan, S. Archer, R. Birdsey, C. Dahm, L. Heath, J. Hicke, D. Hollinger, T. Huxman, G. Okin, R. Oren, J. Randerson, W. Schlesinger, D. Lettenmaier, D. Major, L. Poff, S. Running, L. Hansen, D. Inouye, B.P. Kelly, L Meyerson, B. Peterson, and R. Shaw. U.S. Environmental Protection Agency, Washington, DC, USA.

3. Kundzewicz, Z.W., L.J. Mata, N.W. Arnell, P. Döll, P. Kabat, B. Jiménez, K.A. Miller, T. Oki, Z. Sen, and I.A. Shiklomanov (2007). Freshwater resources and their management. In: Climate Change 2007: Impacts, Adaptation and Vulnerability . Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Parry, M.L., O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson (eds.)]. Cambridge University Press, Cambridge, United Kingdom.

4. CCSP (2009). Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region . A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Titus, J.G. (Coordinating Lead Author), Anderson, K.E., Cahoon, D.R., Gesch, D.B., Gill, S.K., Gutierrez, B.T., Thieler, E.R., Williams, S.J. (Lead Authors). U.S. Environmental Protection Agency, Washington, DC, USA.

5. NRC (2008). Ecological Impacts of Climate Change . National Research Council. The National Academies Press, Washington, DC, USA.

6. CCSP (2008). Preliminary Review of Adaptation Options for Climate-Sensitive Ecosystems and Resources . A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Julius, S.H., J.M. West (eds.), J.S. Baron, B. Griffith, L.A. Joyce, P. Kareiva, B.D. Keller, M.A. Palmer, C.H. Peterson, and J.M. Scott (authors). U.S. Environmental Protection Agency, Washington, DC, USA.

Adaptation Examples in Water

As climate change causes heavy precipitation events to become more frequent, flooding will likely increase in some areas of the country. At the same time, droughts are likely to become more common, especially in arid regions. Both flooding and droughts can degrade water quality. To learn more about how climate change can impact water supply and quality, visit the Water Impacts section.

In areas that will likely see more concentrated rain and flooding, land managers are taking steps to minimize flood hazards. Likewise, in areas where shortages are projected, water utility providers and resource managers are working to increase and protect the water supply. Although not all efforts are designed with adaptation as a primary goal, such actions increase resilience to expected changes in climate. Water management adaptation efforts include a wide variety of activities based on current and anticipated climate change impacts. Specific adaptation approaches include:

• Conserving water and minimizing runoff with climate-appropriate landscaping, such as xeriscaping
• Using water barrels that capture excess rainfall to minimize flooding and maintain a constant supply of water through dry spells
• Protecting valuable resources and infrastructure from flood damage
• Managing rainfall on-site to limit contamination and protect water quality
• Limiting development within vulnerable watersheds

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Xeriscape demonstration garden in Chandler, AZ. Source: City of Chandler, Arizona, Water Conservation Office

The following case studies, examples, and related links are illustrative of water resource management adaptation and are not intended to be comprehensive. To learn about the role of water in adaptation efforts in other sectors visit the Coastal Impacts & Adaptation page, Energy Impacts & Adaptation page, or Agriculture and Food Supply Impacts & Adaptation page.

Local governments plan for water shortages

Household rain barrel collects water during storms. Source: King County, WA, Department of Natural Resources and Parks (2012)

Changes in rain and snow patterns will likely alter the timing and the amount of water available in watersheds and existing reservoirs, especially during the summer months. The West, particularly the Southwest, is projected to have more frequent and severe droughts. ^[1] There are a variety of ways that water utilities and cities can encourage homeowners to protect existing supply, expand future supply, and limit demand.

• Local governments in drought-prone regions promote climate-appropriate landscaping to minimize the demand for water. In the City of Peoria, Arizona, the Public Works and Utilities Department provides technical assistance and offers rebates for "dry landscaping" or xeriscapes. In the Southwest, xeriscapes include desert plants that thrive in dry conditions.
• In cases of severe water shortage and rapid population growth, new water supply strategies such as water reuse, aquifer storage and recovery, and desalination may help meet demand.
• Water efficient appliances use less water than older models. The Metropolitan North Georgia Water Planning District, for example, offers incentives for individuals and businesses that switch to low-flow toilets, showerheads, and faucets.
• Rain barrels are an effective, low-tech way to reuse water on-site. Cities like Chicago, Illinois and Gaithersburg, Maryland offer rebates for residents who purchase rain barrels. These barrels are set up below rain spouts to collect excess runoff from roofs. The benefit is twofold—reducing localized flooding and providing water for landscaping.

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Parts of the U.S. Prepare for More Flooding

The Chicago, Illinois City Hall was retrofitted with a "green roof" in 2001. Source: U.S. Department of Energy (2006)

Parts of the United States, (for example the Northwest, Midwest and Northeast) are projected to experience more frequent and severe heavy rains. ^[1] Cities and counties are strengthening flood protection infrastructure and encouraging development that minimizes runoff.

• Green stormwater infrastructure uses landscape design and technologies to manage stormwater on-site and restore the natural hydrology of the land. Cities like Philadelphia are exploring how to integrate rain gardens, stormwater planters, and green roofs into the urban design.
• Flood prone cities and counties are working with the Federal Emergency Management Agency and the Army Corps of Engineers to identify and build infrastructure to protect people and property impacted by flooding events. The Army Corps of Engineers has several priority projects to protect the New Orleans area from flooding caused by heavy rain and storm surge.

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Cities, the EPA, and local partners protect water quality

As discussed in the Water Resources Impacts section, climate change can affect water quality in a variety of ways. Water utility and infrastructure managers can take a variety of steps to prevent contamination of water supplies, and to protect the ecosystems that help to maintain water quality.

• In some cities, combined sewer systems collect rainwater runoff, domestic sewage, and industrial wastewater in one pipe that are typically transported to a sewage facility for treatment. However, during heavy rain events, these systems can overflow directly into a water body, potentially contaminating water supplies or recreational areas. Limiting rainwater runoff during rainstorms can help avoid overburdening a combined sewer system. For example, increasing the amount of permeable surfaces, such as permeable pavement, can allow water to infiltrate the ground. By using porous materials, builders can reduce localized flooding and the amount of water that runs into sewers. Chicago has incorporated permeable pavements in its Green Alley program.
• Pollutants that enter waterways can quickly disperse and degrade water quality. Increasing the distance between hazardous materials and areas that are likely to flood can prevent contaminants from polluting the water supply.
• Limiting development within a watershed protects the natural ecosystems that often contribute to water quality and regulate flows. For example, the City of Seattle restricts development on land in the Cedar River watershed that feeds water into its reservoir.
• EPA's National Water Program Climate Change Strategy provides an overview of the likely impacts of climate change on the nation's clean and safe drinking water programs. It also identifies goals and strategic actions being implemented by the National Water Program to adapt to those changes. Specific adaptation strategies include improving assessment methods to detect hydrologic changes, incorporating climate change considerations into Clean Water Act programs to protect watersheds, wetlands, oceans and coastal waters, and promoting the development of "green infrastructure" that reduces water contamination and conserve water and energy. ^[2]
• EPA's Climate Ready Water Utilities initiative provides practical tools and resources for drinking water, wastewater, and stormwater utilities to better understand and adapt to climate change impacts.

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Federal Agencies make it easier to protect local water supplies

Several government projects were developed to make it easier for local utilities to manage water resources in a changing climate.

• WaterSense is an EPA partnership program, through which organizations, businesses, and governments work together to promote water conservation through the use of efficient appliances. The WaterSense label helps consumers identify products and services that are at least 20% more efficient than average products without sacrificing performance.
• The U.S. Department of the Interior runs WaterSMART, a program that focuses on improving water conservation and helping water-resource managers make sound decisions about water use. The program also identifies adaptive measures to address climate change and its impact on future water demands. In addition to providing grants for local conservation projects, the Department manages a website where water managers can share ideas and learn from colleagues.
• The Interagency Climate Change Adaptation Task Force developed the National Action Plan: Priorities for Managing Freshwater Resources in a Changing Climate (PDF) to help freshwater resource managers plan for climate change. The report provides six recommendations to help ensure an adequate clean water supply.

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References

1. USGCRP (2009). Global Climate Change Impacts in the United States. Karl, T.R. J.M. Melillo, and T.C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.

2. U.S. EPA (2012). 2012 National Water Program Strategy: Response to Climate Change.