Projected median percentage precipitation change (of 112 climate projections) over the Western United States, 2070–2099 relative to 1950–1979. Source: DOI. Click to enlarge.

• a temperature increase of 5-7 degrees Fahrenheit;
• a precipitation increase over the northwestern and north-central portions of the western United States and a decrease over the southwestern and south-central areas;
• a decrease for almost all of the April 1^st snowpack, a standard benchmark measurement used to project river basin runoff; and
• an 8 to 20% decrease in average annual stream flow in several river basins, including the Colorado, the Rio Grande, and the San Joaquin.

The report notes that projected changes in temperature and precipitation are likely to impact the timing and quantity of stream flows in all western basins, which could impact water available to farms and cities, hydropower generation, fish and wildlife, and other uses such as recreation.

Click to enlarge.

To develop the report, Reclamation used original research and a literature synthesis of existing peer-reviewed studies. Projections of future temperature and precipitation are based on multiple climate models and various projections of future greenhouse gas emissions, technological advancements, and global population estimates. Reclamation will develop future reports to Congress under the authorities of the SECURE Water Act that will build upon the level of information currently available and the rapidly developing science to address how changes in supply and demands will impact water management.

Water is the lifeblood of our communities, rural and urban economies, and our environment, and small changes in water supplies or the timing of precipitation can have a big impact on all of us. This report provides the foundation for understanding the long-term impacts of climate change on Western water supplies and will help us identify and implement appropriate mitigation and adaptation strategies for sustainable water resource management.

—Interior Secretary Ken Salazar

Impacts to water are on the leading edge of global climate change, and these changes pose a significant challenge and risk to adequate water supplies, which are critical for the health, economy, and ecology of the United States.

—Reclamation Commissioner Mike Connor

The Bureau of Reclamation is the largest wholesaler of water in the country, providing water to more than 31 million people and to one out of five Western farmers for irrigation of more than 10 million acres of farmland. Reclamation is also the second largest producer of hydroelectric power in the western United States with 58 power plants generating nearly a billion dollars in power revenues and producing enough electricity to serve 3.5 million homes.

Resources

• SECURE Water Act Report