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Irrigation pipes on Southern California farmland.
Eddie J. Rodriquez/Shutterstock

Late-summer 2014 has brought uncomfortable news for residents of the US Southwest-and I’m not talking about 109-degree heat in population centers like Phoenix.

A new study by Cornell University, the University of Arizona, and the US Geological Survey researchers looked at the deep historical record (tree rings, etc.) and the latest climate change models to estimate the likelihood of major droughts in the Southwest over the next century. The results are as soothing as a thick wool sweater on a midsummer desert hike.

The researchers concluded that odds of a decadelong drought are “at least 80 percent.” The chances of a “megadrought,” one lasting 35 or more years, stands at somewhere between 20 percent and 50 percent, depending on how severe climate change turns out to be. And the prospects for an “unprecedented 50-year megadrought”-one “worse than anything seen during the last 2000 years”­-checks in at a nontrivial 5 to 10 percent.

To the right there’s a map, pulled from the study, showing that the swath of land in question and its risk of a 35-year drought. It extends from Southern California clear to West Texas, encompassing population centers like San Diego, Phoenix, Tucson, and Albuquerque, along with a large chunk of the troubled US-Mexico border. (Note that in northern Mexico, drought prospects are even higher.)

This (paradoxically) chilling assessment comes on the heels of another study (study; my summary), this one released in early August by University of California-Irvine and NASA researchers, on the Colorado River, the lifeblood of a vast chunk of the Southwest. As many as 40 million people rely on the Colorado for drinking water, including residents of Las Vegas, Los Angeles, Phoenix, Tucson, and San Diego. It also irrigates the highly productive winter farms of California’s Imperial Valley and Arizona’s Yuma County, which produce upwards of 80 percent of the nation’s winter vegetables.