The Western United States is the driest it has been in at least 1,200 years, a new study finds.

The region is experiencing a megadrought, now in its 22nd year, and 2021 was one of the driest years ever recorded, researchers wrote in a study published Monday in the journal Nature Climate Change. The megadrought does not show signs of getting better anytime soon, the researchers said, and it’s believed that 42 percent of it can be directly attributed to human-caused climate change triggered by the burning of fossil fuels, The Associated Press reports.

Park Williams, a climate hydrologist at the University of California Los Angeles and the study’s lead author, said 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. 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.”

The researchers studied soil moisture levels in California, Wyoming, Utah, Nevada, Arizona, most of Oregon and Idaho, and much of New Mexico, western Colorado, northern Mexico, and the southwest corners of Texas and Montana. Using tree rings, they were able to get estimates dating back to the year 800.

Williams began studying the current megadrought a few years ago, and didn’t believe it would last as long as a severe, 23-year megadrought that took place in the 1500s. Usually, megadroughts start to get better after 20 years, but Williams said that even though 2019 was a wet year, 2020 and 2021 were extremely dry and “we’re nowhere close to the end.”

Roughly 55 percent of the Western U.S. is in drought, and Williams said while the megadrought will end if there are a few good years of rain, another one will quickly replace it. Jonathan Overpeck, dean of environment at the University of Michigan, told AP that the study, which he was not part of, is “an important wake-up call. 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.”