Quirks & Quarks

Megadrought: will the southwest part of North America be parched for decades?

Climate change could push the area into the worst megadrought in a 1,200 years

Climate change could push the area into the worst megadrought in a 1,200 years

An elderly member of the Navajo Nation receives her monthly water delivery on June 2019 in Thoreau, New Mexico. Rising temperatures associated with global warming have worsened drought conditions on their lands over recent decades. (Spencer Platt/Getty Images)

The southwest of North America may be in the grip of a climate change-driven drought so severe that scientists say it's on track to becoming the worst megadrought of the last millennium.

That's according to a study in the journal Science that combined modern weather observations with 1,200 years of tree-ring data and dozens of climate models. 

"Over the last millennium there were four really distinct [mega]droughts," said Park Williams from Columbia University's Lamont-Doherty Earth Observatory.  Megadroughts they saw in their climate record lasted anywhere from 28 years to nearly a century and were worse than any drought we've seen in the last 400 years. 

Modern megadrought may have already begun

The area Williams studied, from the northern Oregon and Wyoming border down to northern Mexico, has been experiencing persistent drought conditions since about the year 2000.

Areas of southwestern North America affected by drought in the early 2000s; darker colours are more intense. Yellow box shows the study area. (Adapted from Williams et al., Science, 2020)

"The average soil moisture conditions in the last 21 years have been almost identical to the worst soil moisture conditions of the worst 20 year periods of the worst mega droughts of last millennium," he told Quirks & Quarks host Bob McDonald.

"The only difference is that this drought is not yet as long as the megadroughts — but it hasn't had the opportunity to finish."

Climate change today making things much worse

The historical megadroughts Williams studied were due to climate variability due to apparently random changes in ocean circulation.

"The thing about this drought is that we've been helping it look like a megadrought," he said. 

He said when he removed the long-term trend in temperature caused by climate change in the climate models, the severity of the drought went down by about half. 

"Without human caused warming, we still would have had a drought, but the drought would not have been nearly as severe and wouldn't be able to compete with last millennium's megadroughts," added Williams. 

A dried out lake stands near the Navajo Nation town of Thoreau in June 2019 in Thoreau, New Mexico. (Spencer Platt/Getty Images)

He said what scares him is the possibility that the climate variability that led to the previous megadroughts could be superimposed onto the situation the area is facing today. 

"It seems that the writing is on the wall — that even if this drought were not to become a megadrought because of some lucky years in the next decade, it's going to take more and more luck to stay out of megadrought conditions as we move into the future."

Produced and written by Sonya Buyting


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