Mega-drought is defined as any drought as bad as the worst already seen in the 20th century, but lasting much longer, for 35 years or more.
The study led by experts at the Earth Institute at Columbia University is the first to predict that the coming intense dry spells could exceed the decades-long mega-droughts that occurred centuries ago and are blamed for the demise of certain civilizations in the late 13th century.
"We are the first to do this kind of quantitative comparison between the projections and the distant past, and the story is a bit bleak," said Jason Smerdon, a co-author and climate scientist at the Lamont-Doherty Earth Observatory, part of the Earth Institute at Columbia University.
"Even when selecting for the worst mega-drought-dominated period, the 21st century projections make the mega-droughts seem like quaint walks through the Garden of Eden."
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Researchers applied 17 different climate models to analyze the future impact of rising temperatures on regions from Mexico to the United States and Canada.
"The results... Are extremely unfavorable for the continuation of agricultural and water resource management as they are currently practiced in the Great Plains and southwestern United States," said David Stahle, professor in the Department of Geosciences at the University of Arkansas who was not involved in the study.
Currently the western United States has been experiencing a drought for about 11 of the past 14 years.
The research was presented at the American Association for the Advancement of Science annual meeting, and published in a new AAAS online journal called Science Advances.