Lake Mead, the largest man-made reservoir in the United States -- and major water supplier for Las Vegas, Phoenix and other western cities -- could run dry in as little as 13 years.

That's the unsettling news from the Scripps Institution of Oceanography, who said yesterday that the journal Water Resources Research plans to publish a study of theirs that predicts there is a 10 percent chance the reservoir will run out of usable water by 2014 and 50 percent chance the lake will be useless by 2021.

The combination of climate change and growing demand for Colorado River water is to blame for the severe shortages in Lake Mead, where water levels have already fallen to 50 percent of capacity. Of additional concern to desert metropolis' such as Las Vegas is the report's prediction that water levels in the lake could drop too low to allow hydroelectric power generation by 2017.

The researchers -- marine physicist Tim Barnett and climate scientist David Pierce -- used Bureau of Reclamation data on river flows and reservoir levels to make their conclusions. "Without Lake Mead and neighboring Lake Powell, the Colorado River system has no buffer to sustain the population of the Southwest through an unusually dry year, or worse, a sustained drought. In such an event, water deliveries would become highly unstable and variable," the Scripps Institition said yesterday.

This news will do nothing to ease tensions among the seven western states that siphon off Colorado River water, mostly for irrigation. And we're not sure what the Bureau of Reclamation and regional authorities can do, given the report's claim that calculations of scheduled water allocations and climate conditions indicate that the system could run dry even if mitigation measures now being proposed are implemented.