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Index

Drought in the Colorado River Basin

Elevation of Lake Mead, July 1935-October 2010

The decade-long drought in the West has had a severe impact on the water level of Lake Mead. By the end of October 2010, data from the U.S. Department of the Interior Bureau of Reclamation indicated that the level of Lake Mead had dropped to 1082.36 feet, which is the lowest level since the lake was filled in the 1930s. The previous lowest level was 1083.57 feet, reached in March 1956 during the peak of the 1950s drought. This has serious implications for water supplies in Arizona and Nevada.

Lake Mead is one of several reservoirs along the Colorado River. A major water source for the Colorado River is precipitation that falls in the central Rocky Mountains of Colorado, Wyoming, and Utah. This region is the Upper Colorado River Basin. Much of the West has experienced very dry conditions for the last ten years. This decade of drought is reflected in the precipitation received in the Upper Colorado River Basin. The early 2000s were very dry, with the Upper Colorado's Palmer Hydrological Drought Index (PHDI) reaching record low levels during the summer of 2002.

Upper Colorado River Basin Precipitation, Hydrologic Year October-September, 1895-2010
PHDI for Upper Colorado River Basin, January 1900-November 2010
A 2129-year reconstruction of precipitation for northwest New Mexico

Droughts in the West, including in the Upper Colorado Basin, have been getting more widespread and severe during the last 50 to 90 years of instrument-based weather records (large-scale U.S. weather records go back to 1895). Tree ring records provide a useful paleoclimatic index that extends our historical perspective of droughts centuries beyond the approximately 100-year instrumental record. A 2129-year paleoclimatic reconstruction of precipitation for northwest New Mexico indicates that, during the last 2000 years, there have been many droughts more severe and longer-lasting than the droughts of the last 110 years. This has implications for water management in the West. For example, the Colorado Compact is the legal agreement used for allocation of Colorado River waters among the western states. The Compact was negotiated early in the 20th century during a very wet period, which was not representative of the long-term climatic conditions of the West.