A drought more severe than anything in the past 2,000 years could plague the U.S. Southwest some time in the coming century, a study using computer models has suggested.

Researchers at Cornell University, the U.S. Geological Survey and the University of Arizona have run computer models in an effort to assess the chances of a drought of 10 years, 35 years or 50 years happening in the region in the next hundred years.

Including climate change in the models yielded an 80 percent likelihood of a drought lasting a decade, the researchers reported in the journal of the American Meteorological Society.

"This will be worse than anything seen during the last 2,000 years and would pose unprecedented challenges to water resources in the region," says study leader Toby Ault, a Cornell professor of earth and atmospheric sciences.

The models estimate a 20 to 50 percent possibility of a megadrought lasting 35 years and a 5 to 10 percent risk of one lasting for 50 years, the researchers said.

The models suggested that the states of California, New Mexico and Arizona face the greatest increased risks for drought.

California is already in its third year of drought conditions and is currently experiencing D4 "exceptional drought," the most severe classification.

Other states including Oregon, Oklahoma and Texas have been alternating between moderate and exceptional drought.

Climate change represents one of the most worrying factors involved in possible sustained drought, Ault says.

"As we add greenhouse gases into the atmosphere -- and we haven't put the brakes on stopping this -- we are weighting the dice for megadrought conditions," he says.

The researchers also used their computer models to look beyond the U.S., finding possible vulnerabilities to megadroughts in Australia, southern Africa and the Amazon basin of South America.

If temperatures continue to increase with global warming then drought severity will likely get worse, "implying that our results should be viewed as conservative," the study authors wrote.

The findings should be a signal for the West and Southwest to begin looking for mitigation strategies to deal with extended drought, Ault says.

"With ongoing climate change, this is a glimpse of things to come," he says. "It's a preview of our future."

Ault says he's optimistic that now that the risks are known, ways to adapt and adjust will be found.

"After all," he says, "humans are incredibly adaptable creatures, and civilizations in the past have managed water with far fewer resources than we have available to us today."