A U.S. Department of Interior (DOI) report identifies climate change as a growing risk to Western water management and cites warmer temperatures, changes to precipitation, snowpack and the timing and quality of stream flow runoff across major river basins as threats to water sustainability. Water supply, quality and operations; hydropower; groundwater resources; flood control; recreation; and fish, wildlife and other ecological resources in the western states are at risk, according to the report.

“We need to continue to develop collaborative strategies across each river basin to ensure that our nation’s water and power supplies, agricultural activities, ecosystems and other resources all have sustainable paths forward,” says DOI Deputy Secretary Michael Connor.

A hydrologic technician measures stream flow in Homer Creek, near Herman, Idaho. Image credit: Jay Bateman/USGS. The report, which responds to requirements under the Secure Water Act of 2009, shows several increased risks to western U.S. water resources in the 21st century. Specific projections include:

· A temperature increase of 5-7 degrees Fahrenheit by the end of the century;

· A precipitation increase over the northwestern and north-central portions of the western U.S. and a decrease over the southwestern and south-central areas;

· A decrease for almost all of the April 1st snowpack, a standard benchmark measurement used to project river basin runoff; and

· A 7-27% decrease in April-to-July stream flow in several river basins, including the Colorado, the Rio Grande and the San Joaquin.

According to the report, the projections will have specific basin-level impacts, including:

· Southern California: In Southern California, warming and population growth are projected to increase water demand, reliance on imported water and the use of groundwater in the area, requiring development of alternative water supplies, such as recycled water.

· Colorado River Basin: Reductions in spring and early summer runoff could translate into a drop in water supply for meeting irrigation demands and adversely impact hydropower operations at reservoirs.

· Klamath and Truckee River Basins: Warmer conditions may result in increased stress on fisheries, reduced salmon habitat, increased electricity demand, increased water demands for in-stream ecosystems and increased likelihood of invasive species infestations.

· Columbia and Missouri River Basins: Moisture falling as rain instead of snow at lower elevations will increase the runoff during the wintertime rather than the summer, translating to reductions for meeting irrigation demands, adversely impacting hydropower operations and increasing wintertime flood-control challenges.

· Sacramento and San Joaquin River Basins: Earlier-season runoff combined with a potential for increasing upper watershed evapotranspiration may reduce the capacity to store runoff in Reclamation’s Central Valley Project and state water resources reservoirs.

· Rio Grande Basin: Reduced snowpack and decreased runoff likely will result in less natural groundwater recharge. Additional decreases in groundwater levels are projected due to increased reliance on groundwater pumping.

DOI has launched an online tool enabling the public to visualize the regional impacts and potential adaptation options. The tool allows users to check, by basin, how temperature, precipitation and snowpack are projected to be affected by climate change and how climate change may affect runoff and water supplies. The viewer can also check the projected flow of a river at specific points and times of the year and display adaptation options.