U.S. headed for a ‘mega-drought’ in 21st century, scientists warn

New research published in the journal Science Advances finds that the American Southwest and Great Plains in the 21st century risk the worst drought conditions in more than 1,000 years. By 2050, the U.S. could surpass the “mega-drought” conditions of the 12th and 13th centuries, with severe droughts lasting multiple decades.

“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 E. Smerdon, climate scientist at the Lamont-Doherty Earth Observatory and one of the authors on the paper in a press release. “Even when selecting for the worst megadrought-dominated period, the 21st century projections make the megadroughts seem like quaint walks through the Garden of Eden.”

In other words, imagine that the worst droughts of the 20th century — the Dust Bowl of the 1930s or the drought during the 1950s — persisted for 30 years, said Toby Ault, assistant professor of earth and atmospheric scientists at Cornell University.

PBS NewsHour has reported on the drought raging through the American Southwest, California and the Great Plains. The ongoing drought has already strained agriculture and forced municipalities to restrict their water usage.

According the U.S. Drought Monitor, much of the American West has been in a drought for 11 of the past 14 years. NASA estimates that 64 million people are directly affected by drought conditions in the Southwest and Southern Plains.

Scientists attribute the decline of the Pueblo and Anasazi to the last mega-drought in North America in the 13th century.

Authors Smerdon, Ault and Benjamin I. Cook from the NASA Goddard Institute for Space Studies studied the frequency of mega-droughts in North America’s past and the possibility of such dry spells in the future, using climate data from the North American Drought Atlas and climate models. The North American Drought Atlas catalogues drought conditions across the continent from the past 2,005 years based on tree ring data.

In the past, mega-droughts were a result of natural variability, Cook said. Researchers ran 17 different climate models. The models showed “business as usual,” a continued rise in emissions of the greenhouse gases, and a second scenario in which emissions are moderated.

Their results found that human-induced climate change, not natural variability, will be the primary driving force behind these droughts in the future.

“The surprising thing to us was really how consistent the response was over these regions, nearly regardless of what model we used or what soil moisture metric we looked at,” Cook said in press release. “It all showed this really, really significant drying.” The finding is consistent with previous studies, he added.

Ault said these future droughts could be minimized, but carbon emissions need to be lowered immediately.

“The time to act is now. The time to start planning for adaptation is now,” he said. “We need to assess what the rest of this century will look like for our children and grandchildren.”