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Could the southwest of the U.S. be in for a megadrought?

From Mother Jones

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 mid-summer desert hike. 

The researchers concluded that odds of a decade-long drought are “at least 80 percent.” The chances of a “mega-drought,” 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 non-trivial 5 percent to 10 percent.

It gets worse

his (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.

The researchers analyzed satellite measurements of the Earth’s mass and found that the region’s aquifers had undergone a much-larger-than-expected drawdown over the past decade—the region’s farms and municipalities responded to drought-reduced flows from the Colorado River by dropping wells and tapping almost 53 million acre-feet of underground water between December 2004 and November 2013—equal to about 1.5 full Lake Meads, drained off in just nine years, a rate the study’s lead researcher, Jay Famiglietti, calls “alarming.”

Considering how much of the Colorado River Basin, which encompasses swaths of Utah, Colorado, California, Arizona, and New Mexico, are desert, it’s probably not wise to rapidly drain aquifers, since there’s little prospect that they’ll refill anytime soon. And when you consider that that the region faces high odds of a coming mega-drought, the results are even more frightening. (Just before Labor Day, over fierce opposition from farm interests, the California legislature passed legislation that would regulate groundwater pumping—something that has never been done on a state-wide basis in California before. Gov. Jerry Brown is expected to sign it into law.)

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