Climate change is likely to cut water flow in many of the American West's rivers by as much as a fifth, a report from the Interior Department warns. The affected rivers supply water to eight US states.
The report to Congress by the Department's Bureau of Reclamation examines future water supplies across eight major river basins, including the Colorado, Rio Grande and Missouri.
"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," said Interior Secretary Ken Salazar.
"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."
The report predicts a temperature increase of 5-7 degrees Fahrenheit across the region. It foresees an increase in precipitation over the northwestern and north-central portions of the western United States and a decrease over the southwestern and south-central areas.
It says there's likely to be a decrease for almost all of the April 1st snowpack - a standard benchmark measurement used to project river basin runoff - and an 8 to 20 percent fall in average annual stream flow in several river basins, including the Colorado, the Rio Grande, and the San Joaquin.
However, the projected changes in temperature and precipitation are also 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.
"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," says Reclamation Commissioner Mike Connor.