Although the computer models show the drying has already started, they are not accurate enough to know whether the drought is the result of global warming or a natural variation.
"It's really hard to tell," said Connie Woodhouse, a paleoclimatologist at the University of Arizona. "It may well be one of the first events we can attribute to global warming."
The U.S. and southern Europe will be better prepared to deal with frequent drought than most African nations.
For the U.S., the biggest problem would be water shortages. The seven Colorado River Basin states -- Colorado, Wyoming, Utah, Nevada, New Mexico, Arizona and California -- would battle each other for diminished river flows.
Mexico, which has a share of the Colorado River under a 1944 treaty and has complained of U.S. diversions in the past, would join the struggle.
Inevitably, water would be reallocated from agriculture, which uses most of the West's supply, to urban users, drying up farms. California would come under pressure to build desalination plants on the coast, despite environmental concerns.
"This is a situation that is going to cause water wars," said Kevin Trenberth, a scientist at the National Center for Atmospheric Research in Boulder, Colo.
"If there's not enough water to meet everybody's allocation, how do you divide it up?"
Officials from seven states recently forged an agreement on the current drought, which has left the Colorado River's big reservoirs -- Lake Powell and Lake Mead -- about half-empty. Without some very wet years, federal water managers say, Lake Mead may never refill.
In the next couple of years, water deliveries may have to be reduced to Arizona and Nevada, whose water rights are second to California.
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alan.zarembo@latimes.com
bettina.boxall@latimes.com
