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Water: Climate Change and Water

Water Impacts of Climate Change

Climate change has already altered, and will continue to alter, the water cycle. Impacts include warmer air and water, changes in the amounts and distribution of rainfall and snowfall, more intense rainfall and storms, and sea level rise. This page provides information about the water impacts of climate change.

The Water Cycle: Graphic showing the movement of water through the water cycle. A larger version of this graphic is available on the U.S. Geological Survey website.

Water is always in movement, and the natural water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth. Source: U.S. Geological Survey

The Water Cycle

The water cycle is a delicate balance among precipitation, evaporation, and all 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. Increased evaporation may dry out some areas causing moisture to fall as excess precipitation on other areas.

Changes in the amount of rain falling during storms provide evidence that the water cycle is already being affected. Over the past 50 years, the amount of rain falling during the most intense 1 percent of storms increased by almost 20 percent. Warmer 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 whose sources are in mountainous areas.

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Impacts on Water Quantity

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.

How does climate change affect water resources?

"Water is essential to life and is central to society's welfare and to sustainable economic growth. Plants, animals, natural and managed ecosystems, and human settlements are sensitive to variations in the storage, fluxes, and quality of water at the land surface – notably storage in soil moisture and groundwater, snow, and surface water in lakes, wetlands, and reservoirs, and precipitation, runoff, and evaporative fluxes to and from the land surface, respectively. These, in turn, are sensitive to climate change."
Source: U.S. Climate Change Science Program, 2008

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 will challenge water managers to simultaneously meet the needs of growing communities, sensitive ecosystems, farmers, ranchers, energy producers, and manufacturers.

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 Southeast and West (especially the Southwest) have experienced less rain over the past 50 years, as well as increases in the severity and length of droughts.

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 likely will 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.

Freshwater resources along the coasts face risks from sea level rise. As the sea rises, saltwater moves into freshwater areas. This may cause public utilities to find potable water from other sources, including an increase in the need for desalination (or removal of salt from the water) for some coastal freshwater aquifers used as drinking water supplies.

Planners across many sectors will confront the challenge of a changing water supply. They likely will adopt a variety of adaptation practices designed to better conserve our water supplies and improve water recycling, and will develop alternative strategies for water management.

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Impacts on Water Quality

In some areas, increases in runoff, flooding, or sea level rise are a concern. These effects can reduce the quality of water and can damage the infrastructure that we use to treat, transport and deliver water.

Climate change alterations make freshwater environments more susceptible to toxic algal blooms and can lead to proliferation of harmful microbes and bacteria.

Climate change alterations make freshwater environments more susceptible to toxic algal blooms and can lead to proliferation of harmful microbes and bacteria. Photo: USGCRP, 2009.

Warmer air temperatures can raise stream and lake temperatures, which can harm aquatic organisms that live in cold-water habitats, such as trout and salmon. Additionally, warmer water can increase the range of non-native fish species, permitting them to move into previously cold-water streams. The population of native fish species often decreases as non-native fish prey on and out-compete them for food.

Water quality could also suffer in areas experiencing increases in rainfall. For example, 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. 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 and making them unusable, unsafe, or in need of increased water treatment. In addition, as more freshwater is removed from rivers for human use in coastal areas, saltwater may move farther upstream. Drought can also 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.

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Dissolving CO2 increases the hydrogen ion concentration in the ocean, decreasing ocean pH. The increased CO2 comes from volcanic eruptions and fossil fuel emissions. A larger version of this image is available on the National Research Council of the National Academies website.

Dissolving CO2 increases the hydrogen ion concentration in the ocean, decreasing ocean pH. The increased CO2 comes from volcanic eruptions and fossil fuel emissions.
Source: National Research Council of the National Academies



Impacts on Ocean Acidification

Ocean acidification refers to the decrease in the pH of the oceans caused by the uptake of carbon dioxide (CO2) from the atmosphere. Oceans have been absorbing about one-third of the anthropogenic CO2 emitted into the atmosphere since pre-industrial times. As more CO2 dissolves in the ocean, it reduces ocean pH, which changes the chemistry of the water. These changes present potential risks across a broad spectrum of marine ecosystems.
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Impacts of Changes in Water Resources on Other Sectors

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

The Water-Energy Connection: Graphic showing how water and energy are intimately connected. Without energy, there would be limited water distribution, and without water, there would be limited energy production.

Water and energy are intimately connected. Water is used by the power generation sector for cooling and energy is used by the water sector for pumping, treatment and heating. Without energy, there would be limited water distribution, and without water, there would be limited energy production.
Source: U.S. Global Change Research Program

Some regions of the United States, particularly the Northwest, use water to produce energy through hydropower. If climate change results in lower streamflows or changes in the timing of streamflows, it will reduce the amount of hydroelectricity that can be produced. Lower water flows would also reduce the amount of water available to cool fossil-fuel and nuclear power plants.

Tourism and recreation also will be affected by climate change impacts on water supply and quality. 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.

Agriculture and livestock depend on water. Heavy rainfall and flooding can damage crops, increase soil erosion, and delay planting. Additionally, areas that experience more frequent droughts will have less water available for crops and livestock.

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Learn More

To learn more about how climate change will affect water resources, visit:

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1U.S. Global Change Research Program, 2009. Global Climate Change Impacts in the United States (PDF) (12 pp, 1.45MB, About PDF)

2U.S. Climate Change Science Program, 2008. The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States (PDF) (30 pp, 2.8MB, About PDF)

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