This website is the digital version of the 2014 National Climate Assessment, produced in collaboration with the U.S. Global Change Research Program.

For the official version, please refer to the PDF in the downloads section. The downloadable PDF is the official version of the 2014 National Climate Assessment.

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Welcome to the National Climate Assessment

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.

Explore the effects of climate change
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Water Supply

Water quality and water supply reliability are jeopardized by climate change in a variety of ways that affect ecosystems and livelihoods.

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Introduction

Water quality and water supply reliability are jeopardized by climate change in a variety of ways that affect ecosystems and livelihoods.

Surface and groundwater supplies in some regions are already stressed by increasing demand as well as declining runoff and groundwater recharge. In some regions, particularly the southern U.S. and the Caribbean and Pacific islands, climate change is increasing the likelihood of water shortages and competition for water. Water quality is diminishing in many areas, particularly due to increasing sediment and contaminant concentrations after heavy downpours.

Key Message: Changing Rain, Snow, and Runoff

Annual precipitation and river-flow increases are observed now in the Midwest and the Northeast regions. Very heavy precipitation events have increased nationally and are projected to increase in all regions. The length of dry spells is projected to increase in most areas, especially the southern and northwestern portions of the contiguous United States.

Key Message: Droughts Intensify

Short-term (seasonal or shorter) droughts are expected to intensify in most U.S. regions. Longer-term droughts are expected to intensify in large areas of the Southwest, southern Great Plains, and Southeast.

Key Message: Increased Risk of Flooding in Many Parts of the U.S.

Flooding may intensify in many U.S. regions, even in areas where total precipitation is projected to decline.

Key Message: Groundwater Availability

Climate change is expected to affect water demand, groundwater withdrawals, and aquifer recharge, reducing groundwater availability in some areas.

Key Message: Risks to Coastal Aquifers and Wetlands

Sea level rise, storms and storm surges, and changes in surface and groundwater use patterns are expected to compromise the sustainability of coastal freshwater aquifers and wetlands.

Key Message: Water Quality Risks to Lakes and Rivers

Increasing air and water temperatures, more intense precipitation and runoff, and intensifying droughts can decrease river and lake water quality in many ways, including increases in sediment, nitrogen, and other pollutant loads.

Key Message: Changes to Water Demand and Use

Climate change affects water demand and the ways water is used within and across regions and economic sectors. The Southwest, Great Plains, and Southeast are particularly vulnerable to changes in water supply and demand.

Key Message: Drought is Affecting Water Supplies

Changes in precipitation and runoff, combined with changes in consumption and withdrawal, have reduced surface and groundwater supplies in many areas. These trends are expected to continue, increasing the likelihood of water shortages for many uses.

Key Message: Flood Effects on People and Communities

Increasing flooding risk affects human safety and health, property, infrastructure, economies, and ecology in many basins across the U.S.

Key Message: Water Resources Management

In most U.S. regions, water resources managers and planners will encounter new risks, vulnerabilities, and opportunities that may not be properly managed within existing practices.

Key Message: Adaptation Opportunities and Challenges

Increasing resilience and enhancing adaptive capacity provide opportunities to strengthen water resources management and plan for climate change impacts. Many institutional, scientific, economic, and political barriers present challenges to implementing adaptive strategies.

Changes to Water Demand and Use

Water Stress in the U. S. Water Stress in the U. S. Details/Download

Climate change, acting concurrently with demographic, land-use, energy generation and use, and socioeconomic changes, is challenging existing water management practices by affecting water availability and demand and by exacerbating competition among uses and users. In some regions, these current and expected impacts are hastening efficiency improvements in water withdrawal and use, the deployment of more proactive water management and adaptation approaches, and the re-assessment of the water infrastructure and institutional responses.2

Water Withdrawals

Projected Snow Water Equivalent Projected Snow Water Equivalent Details/Download

Total freshwater withdrawals (including water withdrawn and consumed as well as water that returns to the original source) and consumptive uses have leveled off nationally since 1980 at 350 billion gallons of withdrawn water and 100 billion gallons of consumptive water per day, despite the addition of 68 million people from 1980 to 2005.4 Irrigation and electric power plant cooling withdrawals account for approximately 77% of total withdrawals, municipal and industrial for 20%, and livestock and aquaculture for 3%. Most thermoelectric withdrawals are returned back to rivers after their use for power plant cooling, while most irrigation withdrawals are consumed by the processes of evapotranspiration (evaporation and loss of moisture from leaves) and plant growth. Thus, consumptive water use is dominated by irrigation (81%) followed distantly by municipal and industrial (8%) and the remaining water uses (5%). The largest withdrawals occur in the drier western states for crop irrigation. In the east, water withdrawals mainly serve municipal, industrial, and thermoelectric uses. Some of the largest demand increases are projected in regions where groundwater aquifers are the main water supply source, such as the Great Plains and parts of the Southwest and Southeast. The projected water demand increases (shown below) combined with potentially declining recharge rates threaten the sustainability of many aquifers.

Projected Changes in Water Withdrawals

Projected Changes in Water Withdrawals

Without Climate ChangeWith Climate Change

The effects of climate change, primarily associated with increasing temperatures and potential evapotranspiration, are projected to significantly increase water demand across most of the United States. Maps show percent change from 2005 to 2060 in projected demand for water assuming (a) change in population and socioeconomic conditions consistent with the A1B emissions scenario (increasing emissions through the middle of this century, with gradual reductions thereafter), but with no change in climate, and (b) combined changes in population, socioeconomic conditions, and climate according to the A1B emissions scenario. (Figure source: Brown et al. 20133)

Details/Download

Water Quality

Lower and more persistent low flows under drought conditions as well as higher flows during floods can worsen water quality. Increasing precipitation intensity, along with the effects of wildfires and fertilizer use, are increasing sediment, nutrient, and contaminant loads in surface waters used by downstream water users6,7 and ecosystems in some places. Changing land cover, flood frequencies, and flood magnitudes are expected to increase mobilization of sediments in large river basins.8

Water Supplies Projected to Decline

Water Supplies Projected to Decline

No Climate Change EffectsClimate Change Effects

Climate change is projected to reduce water supplies in some parts of the country. This is true in areas where precipitation is projected to decline, and even in some areas where precipitation is expected to increase. Compared to 10% of counties today, by 2050, 32% of counties will be at high or extreme risk of water shortages. Numbers of counties are in parentheses in key. Projections assume continued increases in greenhouse gas emissions through 2050 and a slow decline thereafter (A1B scenario). (Figure source: Reprinted with permission from Roy et al. 2012.5 Copyright American Chemical Society).

Details/Download

Key Message: Cascading Events

Energy, water, and land systems interact in many ways. Climate change affects the individual sectors and their interactions; the combination of these factors affects climate change vulnerability as well as adaptation and mitigation options for different regions of the country.

Key Message: Options for Reducing Emissions and Climate Vulnerability

The dependence of energy systems on land and water supplies will influence the development of these systems and options for reducing greenhouse gas emissions, as well as their climate change vulnerability.

Key Message: Challenges to Reducing Vulnerabilities

Jointly considering risks, vulnerabilities, and opportunities associated with energy, water, and land use is challenging, but can improve the identification and evaluation of options for reducing climate change impacts.

Energy, Water, and Land Use

Energy, Water, Land, and Climate Interactions Energy, Water, Land, and Climate Interactions Details/Download

Energy production, land use, and water resources are linked in complex ways. Electric utilities and energy companies compete with farmers and ranchers for water rights in some parts of the country. Land-use planners need to consider the interactive impacts of strained water supplies on cities, agriculture, and ecological needs. Across the country, these intertwined sectors will witness increased stresses due to climate changes that are projected to reduce water quality and/or quantity in many regions and change heating and cooling electricity demand, among other impacts.

References

  1. Averyt, K., J. Fisher, A. Huber-Lee, A. Lewis, J. Macknick, N. Madden, J. Rogers, and S. Tellinghuisen, 2011: Freshwater Use by US Power Plants: Electricity’s Thirst for a Precious Resource. A Report of the Energy and Water in a Warming World initiative. 62 pp., Union of Concerned Scientists. URL

  2. Brown, T. C., R. Foti, and J. A. Ramirez, 2013: Projecting fresh water withdrawals in the United States under a changing climate. Water Resources Research, 49, 1259-1276, doi:10.1002/wrcr.20076. URL

  3. Kenny, J. F., N. L. Barber, S. S. Hutson, K. S. Linsey, J. K. Lovelace, and M. A. Maupin, 2009: Estimated Use of Water in the United States in 2005. U.S. Geological Survey Circular 1344. 52 pp., U.S. Geological Survey, Reston, VA. URL

  4. Osterkamp, W. R., and C. R. Hupp, 2010: Fluvial processes and vegetation--Glimpses of the past, the present, and perhaps the future. Geomorphology, 116, 274-285, doi:10.1016/j.geomorph.2009.11.018.

  5. Pietrowsky, R. et al., 2012: Water Resources Sector Technical Input Report in Support of the U.S. Global Change Research Program, National Climate Assessment - 2013. 31 pp.

  6. Pruski, F. F., and M. A. Nearing, 2002: Climate-induced changes in erosion during the 21st century for eight U.S. locations. Water Resources Research, 38, 34-1 - 34-11, doi:10.1029/2001WR000493. URL

  7. Pruski, F. F., and M. A. Nearing, 2002: Runoff and soil-loss responses to changes in precipitation: A computer simulation study. Journal of Soil and Water Conservation, 57, 7-16.

  8. Roy, S. B., L. Chen, E. H. Girvetz, E. P. Maurer, W. B. Mills, and T. M. Grieb, 2012: Projecting water withdrawal and supply for future decades in the U.S. under climate change scenarios. Environmental Science & Technology, 46, 2545−2556, doi:10.1021/es2030774.

  9. Skaggs, R., K. Hibbard, P. Frumhoff, T. Lowry, R. Middleton, R. Pate, V. Tidwell, J. Arnold, K. Avert, A. Janetos, C. Izaurralde, J. Rice, and S. Rose, 2012: Climate and Energy-Water-Land System Interactions. Technical Report to the U.S. Department of Energy in Support of the National Climate Assessment. PNNL-21185. 152 pp., Pacific Northwest National Laboratory, Richland, Washington. URL

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.

United States Global Change Research Program logo United States Global Change Research Program participating agency logos