Last 22 years are also close to surpassing duration of multidecade drought in the 1500s, according to new research
by Talal Ansari, The Wall Street Journal, February 14, 2022
In the American West, the last 22 years have been the driest period since at least 800 A.D., according to a new study.
The drought, which began in 2000, is also on track to surpass the duration of a megadrought in the 1500s, according to Park Williams, lead author of the study, which was published Monday in the journal Nature Climate Change. While there is no one definition for megadrought, the phrase is generally used to signify a drought that has persisted for decades.
“Rather than starting to die away after wet years in 2017 and 2019, the 2000s drought has ramped up with authority in 2020-2021, making clear that it’s now as strong as it ever was,” said Mr. Williams, a climate scientist at the University of California, Los Angeles.
The study found that around 42% of the current drought can be attributed to climate change from human activity. It looked at 29 models that simulated a world without humans to see how human activity has affected the current drought’s duration.
Mr. Williams and his fellow researchers focused on a part of the U.S. that includes all of California, Nevada, Arizona and Utah, as well as portions of Oregon, Wyoming, Colorado, New Mexico, Northern Mexico. Small sections of both Texas and Montana were also included.
“Up to this point, 2002 was by far the worst year of the 2000s drought, and the driest year in nearly 300 years,” Mr. Williams said, adding that drought severity in 2021 was nearly identical to that of 2002. “So now two of the driest years in nearly 300 years have occurred just 20 years apart and within the same extended drought period,” he said.
Exceptionally dry soil in 2021 allowed the current drought to overtake the 1500s megadrought as the driest 22-year period in the region since 800 A.D., the study said.
The scientists primarily looked at thousands of tree ring samples to compare the effects of the current drought with previous ones, in addition to records of soil moisture. Generally speaking, tree rings are wider in years with more moisture, and less in dry years.
The study is an update of one originally published in 2020, which evaluated the long-term historical context of the drought in the U.S. West, looking at conditions from 2000-18. With the persistence of drought conditions, and an especially dry 2021, Mr. Williams said they wanted to recontextualize the current situation with historic droughts in the region.
The researchers forecast the current drought will very likely persist through 2022, which would match, and possibly surpass, the duration of the late-1500s megadrought. That drought lasted 23 years, and after 22 years, conditions were improving, not persisting, Mr. Williams said.
“After 2021, it’s clear that at 22 years old, there is no evidence that the 2000s drought is starting to relent,” he said.
Write to Talal Ansari at [email protected]