Megadrought in Western U.S. 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 new study finds.

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, according to a study Monday in the journal Nature Climate Change

According to the study, 42% can be attributed directly to climate change.
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“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.”

Williams studied soil moisture levels in the West—a box that includes California, Wyoming, Utah, Nevada, Arizona, most of Oregon and Idaho, much of New Mexico, western Colorado, northern Mexico, and the southwest corners of Montana and Texas—using modern measurements and tree rings for estimates that go back to the year 800. That’s about as far back as estimates can reliably go with tree rings.

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. He said that 2019 had been a dry year, so the west drought could be ending.

The region was dry in 2021 and 2020.

According to U.S. drought monitor, California was in an official drought state from May through December 2021. At least three quarters of California’s population was among the two highest drought levels between June and Christmas.

“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. According to Williams, the current drought is about 5% less severe than that of the 1500s.

A drought monitor shows that 55% is currently in drought, with 13% of those affected by the most severe drought.

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

“I was wondering if we’d ever see a year like 2002 again in my life and in fact, we saw it 20 years later, within the same drought,” Williams said. The two drought years of 2002 and 2021 had a statistical tie. However, it was still below 1580 for the worst single-year.

According to scientists, climate change caused by fossil fuel burning is leading to higher temperatures and more evaporation.

Williams used 29 models to create a hypothetical world with no human-caused warming then compared it to what happened in real life—the scientifically accepted way to check if an extreme weather event is due to climate change. His research showed that human-caused global warming is responsible for 42% of droughts. According to him, the megadrought could have ended without climate change as 2005 and 2006 were wet enough for it to be broken.

The study “is an important wake-up call,” said Jonathan Overpeck, dean of environment at the University of Michigan, who wasn’t part of the study. “Climate change is literally baking the water supply and forests of the Southwest, and it could get a whole lot worse if we don’t halt climate change soon.”

Williams claimed that drought and heat are directly linked to the increase in wildfires, which have decimated the West for many years. Dry fuel is what drought and heat provide for fires.

Williams stated that this megadrought would end eventually due to the good fortune of some rainy years. Another one will then begin.

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.”


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