Impacts of climate change on water resources
Climate change has already altered and will continue to alter snowpack and streamflows. This affects where, when, and how much water is available for all users.
A reliable supply of water is vital for communities, businesses, industries, the environment, and quality of life. Washington communities rely to varying degrees on a snow-fed water supply to provide safe and clean drinking water. The irrigated agriculture industry, which helps drive the local and state economy, relies on water to irrigate crops. That same water also feeds rivers and streams that support salmon, a state icon and valuable commercial fishery. Further, Washington’s abundant hydropower resources supply two-thirds of the electricity for the state.
The impacts of climate change will intensify current challenges in managing water resources. The state’s water resources are already under stress from:
- Excessive water withdrawals
- Increasing conflicts among water users and demands on water resources
- Degrading water quality
- More frequent and intense droughts and floods
- Loss of species, habitats, and ecosystems
Climate change will increase uncertainty in the future of Washington's water supply. It will become more difficult to maintain an adequate supply of water for communities, agriculture, and fish and wildlife. As the climate shifts, the timing and volume of stream flows will change due to reduced snowpack and earlier snowmelt.
Drought risk and competition for water supplies
Climate change is expected to increase the risk of summer water shortages and increased demand for water, which will intensify competition for instream and out-of-stream uses.
Water shortages are projected to occur more frequently in the Yakima Basin, and the current reservoir system will likely face difficulty supplying water to all users, especially those with junior water rights. The average production of apples and cherries could decline by approximately $23 million in the 2020s and by $70 million in the 2080s.
Salmon and other fish rely on timely, abundant, cold, clean water to spawn and rear young. Projected changes in climate would increase fall and winter flooding. As peak river flows shift to earlier in the spring, salmon rearing, migration, and spawning are negatively affected. Low flows in late spring and summer result in warmer water which holds less oxygen and stresses fish. Increased summer stream temperatures may exceed tolerable limits for coldwater fish. Changing temperatures in lakes, Puget Sound, and the ocean coastal waters could decrease the available food that healthy salmon populations rely on.
Summertime hydropower production is likely to decline by 9 to 11 percent by the 2020s. Meanwhile, summer demand for energy will increase significantly due to higher electricity needs from air conditioning and population growth.
Puget Sound water supplies
Urban water supply systems in Puget Sound will collect less water in their reservoirs in late spring and early summer. Climate change impacts could result in water demand increases of as much as 12 percent by 2060. Many of the region’s water utilities have adapted in the past to fluctuations in water supplies and are actively implementing and planning long-term adaptations to respond to climate change challenges.
Small water systems and groundwater
Increased drought risk could alter drinking water supplies for small public, private, and independent water systems. Many communities in rural areas rely on groundwater, which could be affected by climate change. Reductions in spring and summer streamflow could limit surface water supplies, triggering heavier reliance on groundwater. On the plus side, warmer, wetter winters could increase the amount of water available for groundwater recharge. The impacts of climate change on groundwater sources of supply are still not well understood and need further study.
Drought stress is likely to reduce forest productivity in Eastern Washington. The area of severely water-limited forests is projected to increase 32 percent by the 2020s and an additional 12 percent in the 2040s and 2080s. Drought-stressed forests are more susceptible to mountain pine beetle outbreaks which have devastated forests and increased wildfire intensity across the west.
Warmer temperatures and reductions in summer precipitation will likely increase the areas burned by wildfire. Wildfires disrupt the watershed processes through soil erosion, warmer water temperatures, increased stormwater runoff and turbidity, and loss of forest canopy. These changes alter the soil’s capacity to retain water and recharge aquifers.
Reductions in summer water levels could affect the navigability of rivers and lakes in the region, although the risk is not well understood.
Less snow and loss of natural water storage
During the winter, when the majority of precipitation occurs, snow accumulates in upper elevations and forms a natural reservoir that stores water during times when demands are relatively low. As the climate warms, more precipitation falls as rain and less as snow, leaving less water naturally stored in snowpack and glaciers. The snow melts earlier in the spring, and less water is available to feed streams in the late summer when demands for water are highest.
Widespread declines in spring snowpack have already occurred across the western U.S., especially since the 1950s. Greater losses in snowpack have been observed in mid-elevation mountain ranges such as the Cascades, where sensitivity to changes in temperature is high. Snow is melting earlier, and peak runoff occurs from 1 to 4 weeks earlier across much of the western U.S. than in the 1950s.
These patterns are expected to continue and further alter the hydrologic behavior of many watersheds in Washington. Under a moderate emissions modeling scenario, spring snowpack levels across the state are projected to decrease 29 percent by the 2020s, 44 percent by the 2040s, and 65 percent by the 2080s, relative to the 1971-2000 average.
Content on the web page was adapted from Preparing for a Changing Climate: Washington State's Integrated Climate Response Strategy. Please read the full publication for citations and references.