The Bureau of Reclamation projects that precipitation and runoff will decline across portions of the Lower Colorado River Basin by the end of the 21st century due to climate change, though major reservoirs like Lake Mead and Lake Powell (above) should be able to adjust to the reduced water flows. Photo courtesy of Reclamation.
Climate change will likely reduce flows in the West's major river basins by as much as 20 percent by the end of the 21st century, according to a report issued by the Interior Department this week.
The report, released by the Bureau of Reclamation to help implement the 2009 Secure Water Act, said streamflows in eight basins could drop as the mercury rises between 5 and 7 degrees by the end of the century.
The "Climate Change and Water 2011" report is primarily a synthesis of existing scientific literature, although it also includes an original assessment of new data culled from the eight river basins on the implications of climate change for snowpack and hydrology.
The four basins in the northern reaches of the West -- the Upper Colorado, Columbia, Missouri and Sacramento -- will generally see more precipitation, while four in the Southwest -- the Lower Colorado, Rio Grande, San Joaquin and Truckee -- will see less water.
"Projections of future hydrology suggest that warming and associated loss of snowpack will persist over much of the Western United States," the report states. "However, not all locations are projected to experience similar changes."