New Study Turns Up the Heat on Megadrought Predictions

Monday, February 16, 2015

Now we're cookin'.

There have been many scientific studies of late assessing how long and how intense drought conditions in California might be in the foreseeable future. The researchers who produced a new study in the journal Science Advances dismiss them all because of their “uncertainty about drought projections for these regions.”

Three scientists from Cornell University, NASA’s Goddard Institute for Space Studies and the Lamont-Doherty Earth Observatory of Columbia University have no doubt: Mother Nature is about to go medieval on California and a big chunk of the United States:  

“We have demonstrated that the mean state of drought in the late 21st century over the Central Plains and Southwest will likely exceed even the most severe megadrought periods of the Medieval era in both high and moderate future emissions scenarios, representing an unprecedented fundamental climate shift with respect to the last millennium.”

By megadrought, they mean, “levels of risk of 80% of a 35-year-long drought by the end of the century, if climate change goes unmitigated,” co-author Toby Ault from Cornell told the BBC.

By “high and moderate future emissions scenarios,” they mean the region is screwed pretty much no matter what it does. The megadroughts in the country’s Southwest between 1100 and 1400 contained periods of dryness lasting from 20 to 50 years each.

Ault was a co-author of a study released last September that used some of the same data to paint an equally bleak picture of the future, but contained a caveat: “We stress that our results have only used precipitation, yet temperature may play a substantial role in driving or exacerbating drought.”

The new study focuses on temperature—and supports the earlier study’s warning that “future drought severity will be exacerbated by increases in temperature, implying that our results should be viewed as conservative.” Higher temperatures from global warming will evaporate whatever water is around at accelerated rates.

“The 21st-century projections make the [previous] megadroughts seem like quaint walks through the garden of Eden,” co-author Jason Smerdon of Columbia told the London Guardian.

The new study used 17 climate models to analyze and project the effects of temperature, as well as data from tree rings, which reflect the effects of precipitation. Records of soil moisture, rainfall and evaporation records in the region were also factored in.

In a comment by Ault that was meant to pass as a note of optimism, he told the BBC last week,

“The records we have of past mega-droughts are based on tree-ring width estimates, and if you think that through, that's a little bit encouraging because it means the events weren't so bad as to kill off all the trees. . . . It doesn't mean no water—it just means significantly less water.” 

–Ken Broder


To Learn More:

US Faces Worst Droughts in 1,000 Years, Predict Scientists (by Suzanne Goldenberg, London Guardian)

The Megadrought Is Coming: Climate Scientists Predict Decade Long Droughts for Much of America (by Steven Searls, Daily Kos)

Southwest and Great Plains Could Face Worst “Megadroughts” in Modern History, Study Finds (by Ari Phillips, ThinkProgress)

The United States of Megadrought (by Eric Holthaus, Slate)

US “at Risk of Mega-Drought Future” (by Jonathan Amos, BBC)

80% Chance of 10-Year Drought in Southwest; 50% for a Megadrought (by Ken Broder, AllGov California)

Unprecedented 21st Century Drought Risk in the American Southwest and Central Plains (by Benjamin I. Cook, Toby R. Ault and Jason E. Smerdon, Science Advances)

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