2007 climate study predicted permanent drought in Southwest [View all]

[Kablooie]

May 2007

Aridity has always been the defining feature of the American Southwest, even as large-scale hydraulic engineering has allowed cities such as Phoenix and Las Vegas to burst from the desert floor.

But according to a sobering new study, the Southwest’s aridity is about to get worse. Published in the April 9 issue of Science, “Model Projections of an Imminent Transition to a More Arid Climate in Southwestern North America” predicts that climate change will permanently alter the landscape of the Southwest so severely that conditions reminiscent of the Dust Bowl days of the 1930s could become the norm within a few decades.

“Our study suggests a perpetual arid condition over the American Southwest,” says Jian Lu, a postdoctoral researcher in ASP/CGD who is an author of the study.

Of the 19 different computer models that the research team used for the study, all but one showed a drying trend in the swath of North America between Kansas, California, and northern Mexico. The models predicted an average 15% decline in runoff for the Southwest between 2021 and 2040, compared to the average surface moisture between 1950 and 2000.

The Southwest’s future droughts are expected to be of a different nature than those that have afflicted the region in the past.

As the atmosphere warms from climate change, scientists expect the Hadley cell to expand its reach, bringing hot, dry air to a larger swath of the Middle East, Mediterranean, and North America, including the Southwest. “In the future warmed climate,” Jian explains, “the Hadley cell and the subtropical high should expand poleward, which tends to block rain coming through from the Pacific.”

For the study, the research team assumed that greenhouse gases would continue to rise from today’s level of 380 parts per million until beginning a decline around 2050, measuring 720 parts per million in 2100.

http://www.ucar.edu/communications/staffnotes/0705/drought.shtml