Study says global warming ups odds of Southwest megadrought

Heat-trapping greenhouse gases may dessicate Colorado River Basin

The paradox of water in the desert, illustrated by a NASA satellite image of the Colorado River.
Megadroughts ahead? Satellite photo of the Colorado River Basin via NASA.

Staff Report

It’s very likely the southwestern U.S. will be hit by droughts unlike any seen since the region was settled by Europeans. Global warming has driven the odds of a 10-year drought to at least 50 percent, and the chances of a 35-year megadrought range from 20 to 50 percent during the next century, according to a new study led by researchers with Cornell, the University of Arizona and the U.S. Geological Survey.

Global warming is “weighting the dice” for megadroughts, said lead study author Toby Ault, explaining that the buildup of greenhouse gases is shifting the climate dramatically. The study is set to be published in an upcoming issue of the  American Meteorological Society’s Journal of Climate.

Current widespread drought conditions across much of California, as well as parts of  Oregon, Arizona, New Mexico, Oklahoma and Texa are a preview of our future, Ault said.

While the 1930s Dust Bowl in the Midwest lasted four to eight years, depending upon location, a megadrought can last more than three decades, which could lead to mass population migration on a scale never before seen in this country.

Ault said that the West and Southwest must look for mitigation strategies to cope with looming long-drought scenarios. “This will be worse than anything seen during the last 2,000 years and would pose unprecedented challenges to water resources in the region,” he said.

The study also suggested that chances of drought could decrease in northwestern states, including Washington, Montana, Idaho.

Tree ring studies in the Colorado River Basin show that long-term droughts have occurred in the region every 400 to 600 years. But by adding the influence of growing greenhouse gas in the atmosphere, the drought models – and their underlying statistics – are now in a state of flux.

Beyond the United States, southern Africa, Australia and the Amazon basin are also vulnerable to the possibility of a megadrought. With increases in temperatures, drought severity likely will worsen, “implying that our results should be viewed as conservative,” the study reports.

In the study, the authors wrote that “Business-as-usual emissions of greenhouse gases will drive regional warming and drying, regardless of large precipitation uncertainties. We find that regional temperature increases alone push megadrought risk above 70, 90, or 99 percent by the end of the century, even if precipitation increases moderately, does not change, or decreases, respectively.”

The study, “Assessing the Risk of Persistent Drought Using Climate Model Simulations and Paleoclimate Data,” was also co-authored by Julia E. Cole, David M. Meko and Jonathan T. Overpeck of University of Arizona; and Gregory T. Pederson of the U.S. Geological Survey. The National Science Foundation, the National Center for Atmospheric Research, the U.S. Geological Survey and the National Oceanic and Atmospheric Administration funded the research.

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