BATHTUB RING. Water levels in Lake Mead have dropped significantly in recent years, as chronicled by the white mineral deposits on rocks that were formerly submerged
http://www.sciencenews.org/articles/20080223/fob2.asp
Week of Feb. 23, 2008; Vol. 173, No. 8 , p. 115
Going Down: Climate change, water use threaten Lake Mead
by Sid Perkins
Thanks in part to the worst drought in the Southwest in the past 500 years (SN: 6/26/04, p. 406), Lake Mead is now at about 50 percent capacity. If current allocations of water persist, there's a 50 percent chance that by 2023 Lake Mead won't provide water without pumping, and a 10 percent chance that it won't by 2013. Moreover, there's a 50 percent chance that Hoover Dam won't be able to generate power by 2017, the researchers estimate.
"We were stunned at the magnitude of the problem and how fast it was coming at us," says Barnett.
Results of the new study are "fairly provocative, an eye-opener," says Connie Woodhouse, a climatologist at the University of Arizona in Tucson. Using estimates of river flow based on an average of the past century may be optimistic, she adds, because tree ring–based reconstructions of the region's climate suggest that the 20th century was one of the wettest in the past 500 years. "The more we learn about the Colorado River and its hydrology, the more worried we need to be," says Peter H. Gleick, a hydrologist at the Pacific Institute in Oakland, Calif.