Ottawa Citizen

Major dry spell looms in the U.S.

‘Megadrough­t’ forecast for latter half of century

- NICK ALLEN

A broad swath of the western United States is likely to be hit by a “megadrough­t” lasting decades in the second half of this century, according to a new study.

Scientists from NASA and Cornell and Columbia universiti­es, said there would be weather conditions that were unpreceden­ted in the last millennium.

Benjamin Cook, a climatolog­ist at NASA’s Goddard Institute for Space Studies and lead author of the study, said: “Natural droughts like the 1930s Dust Bowl and the current drought in the (U.S.) southwest have historical­ly lasted maybe a decade or a little less. What these results are saying is we’re going to get a drought similar to those events, but it is probably going to last at least 30 to 35 years.

“Nearly every year is going to be dry toward the end of the 21st century compared with what we think of as normal conditions now. We’re going to have to think about a much drier future in western North America.”

The projected period of extreme dryness would affect a vast area of the U.S. southwest and central plains stretching from northern Texas to the Dakotas and including California, Colorado, Nevada and Arizona.

Evidence from tree rings shows there were decades-long megadrough­ts in the region during the so-called medieval climate anomaly in the 12th and 13th centuries. But the latest study said the looming event would be worse. The impact would also be greater because of population growth, which would cause water shortages.

Scientists based their dire prediction­s on 17 computer climate models which simulated various levels of carbon dioxide in the atmosphere.

They concluded there was an 80 per cent chance the western U.S. would have a megadrough­t toward the end of the 21st century. The research was presented at an annual meeting of the American Associatio­n for the Advancemen­t of Science and published in the journal Science Advances.

California is already in the fourth year of an extended drought, with 40 per cent of the state classified as in “extreme drought.”

Farmers have seen crops wither and cities have imposed water restrictio­ns.

But many scientists agree that is a naturally occurring event.

In predicting future megadrough­ts the authors of the new study said greenhouse gas emissions are increasing the likelihood of them happening. Toby Ault, an assistant professor at Cornell University and the study’s co-author, said: “We’re not necessaril­y locked into these levels of megadrough­t risk if we slow the effects of rising greenhouse gas on global temperatur­es.

“I was honestly surprised at just how dry the future is likely to be. I look at these future megadrough­ts like a slow-moving natural disaster.”

 ??  MARK RALSTON/AFP/GETTY IMAGES ?? Boat docks lie on the dried-up lake bed of Huntington Lake, a reservoir in Fresno County, California, which is at only 30 per cent capacity as a severe drought affects the state.
 MARK RALSTON/AFP/GETTY IMAGES Boat docks lie on the dried-up lake bed of Huntington Lake, a reservoir in Fresno County, California, which is at only 30 per cent capacity as a severe drought affects the state.

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