The current megadrought in the western United States has broken previous records for the driest 22-year period in the region since the year 800 C.E., a new study published in Nature Climate Change shows. The drought has been exacerbated by human-caused climate change and is likely to continue for at least another year, the authors found.
“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,” study lead author Park Williams, a climate hydrologist at the University of California, Los Angeles, tells Seth Borenstein for the Associated Press. “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 authors analyzed data from tree ring patterns for information about soil moisture over the years, and confirmed their measurements against historical climate data.
“Every year, a tree grows an annual growth ring, and in a wet year, the ring will be really wide because the tree grows a lot," Williams tells KCRA’s Heather Waldman. "In a dry year, the tree grows a little bit.”
Without human-caused climate change, the current drought would not be nearly as severe, per the study. The authors estimate that 42 percent of the soil moisture deficit from 2000 to 2021 can be attributed to human-caused climate change.
The study builds upon previous research from Williams, which found that 2000 to 2018 was the second driest 19-year span in 1,200 years. But an exceptionally dry summer in 2021 pushed the current drought to the top, Williams tells the New York Times’ Henry Fountain. That summer, the country’s two largest reservoirs, Lake Mead and Lake Powell, “reached their lowest levels on record, triggering unprecedented restrictions on Colorado River usage,” the study states.
As of January 2022, Lake Mead, the country’s largest reservoir, is at just 34 percent of its capacity. The Lake Mead reservoir provides water to 25 million people in southwestern states, including California. Lake Powell, the second largest reservoir, is at only 27 percent capacity. In April 2021, California’s governor declared a drought state of emergency, which was expanded last October.
It’s “an important wake-up call,” says Jonathan Overpeck, dean of environment at the University of Michigan, who wasn’t part of the study, to the Guardian’s Gabrielle Canon. “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.”