US west megadrought worsens to driest in at least 1,200 years

The American West’s megadrought deepened so much last year that it is now the driest in at least 1,200 years and is a worst-case climate change scenario playing out live.

A dramatic drying in 2021—about as dry as 2002 and one of the driest years ever recorded for the region—pushed the 22-year drought past the previous record-holder for megadroughts in the late 1500s and shows no signs of easing in the near future.

“Climate change is changing the baseline conditions toward a drier, gradually drier state in the West and that means the worst-case scenario keeps getting worse,” said study lead author Park Williams, a climate hydrologist at UCLA. “This is right in line with what people were thinking of in the 1900s as a worst-case scenario. But today I think we need to be even preparing for conditions in the future that are far worse than this.”

A few years ago, Williams studied the current drought and said it qualified as a lengthy and deep “megadrought” and that the only worse one was in the 1500s. He figured the current drought wouldn’t surpass that one because megadroughts tended to peter out after 20 years. And, he said, 2019 was a wet year so it looked like the western drought might be coming to an end. But the region dried up in late 2020 and 2021.

“For this drought to have just cranked up back to maximum drought intensity in late 2020 through 2021 is a quite emphatic statement by this 2000s drought saying that we’re nowhere close to the end,” Williams said. This drought is now 5% drier than the old record from the 1500s, he said.

The drought monitor says 55% of the U.S. West is in drought with 13% experiencing the two highest drought levels.

This megadrought really kicked off in 2002—one of the driest years ever, based on humidity and tree rings, Williams said.

Eventually, this megadrought will end by sheer luck of a few good rainy years, Williams said. But then another one will start.

Daniel Swain, a UCLA climate scientist who wasn’t involved in the study, said climate change is likely to make megadrought “a permanent feature of the climate of the Colorado River watershed during the 21st century.”

Graphic showing changes in the global land area affected by severe drought per month since 1950.

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