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 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.

The study calculated that 42% of this megadrought can be attributed to human-caused climate change.

"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.