Lake Mead

Photo: Simon Norfolk/NB Pictures, for The New York Times

Draining

The 100-foot-high bathtub ring left by the dwindling waters of Lake Mead, behind Hoover Dam.

Scientists sometimes refer to the effect a hotter world will have on this country’s fresh water as the other water problem, because global warming more commonly evokes the specter of rising oceans submerging our great coastal cities. By comparison, the steady decrease in mountain snowpack — the loss of the deep accumulation of high-altitude winter snow that melts each spring to provide the American West with most of its water — seems to be a more modest worry. But not all researchers agree with this ranking of dangers. Last May, for instance, Steven Chu, a Nobel laureate and the director of the Lawrence Berkeley National Laboratory, one of the United States government’s pre-eminent research facilities, remarked that diminished supplies of fresh water might prove a far more serious problem than slowly rising seas. When I met with Chu last summer in Berkeley, the snowpack in the Sierra Nevada, which provides most of the water for Northern California, was at its lowest level in 20 years. Chu noted that even the most optimistic climate models for the second half of this century suggest that 30 to 70 percent of the snowpack will disappear. “There’s a two-thirds chance there will be a disaster,” Chu said, “and that’s in the best scenario.”

http://www.nytimes.com/2007/10/21/magazine/21water-t.html?ref=magazine