Dried lake bed bakes in the sun at Nicasio Reservoir in Nicasio, California, on July 10, 2021. File Photo by Terry Schmitt/UPI | License Photo
Feb. 14 (UPI) -- The "megadrought" that has gripped southwestern North America for more than two decades is the driest such event in the region in at least 1,200 years, according to research published Monday.
The study, led by University of California-Los Angeles geographer Park Williams and published in the journal Nature Climate Change, found that rapid intensification of the drought in the last several years has placed it into a rare category of severity.
The authors, using scientific reconstructions going as far back as A.D. 800, found that the soil moisture deficit recorded in the region between 2000 and 2018 was exceeded only once -- by a megadrought in the late 1500s.
But due to the extremely dry conditions of last year, even that long-ago event has now been surpassed, they found.
Thanks to "exceptional drought severity" in 2021, the last 22 years have emerged as the driest 22-year period in the region since at least A.D. 800. And because the drought is "very likely" to persist throughout this year, the current drought will match the duration of the late-1500s megadrought, the researchers predicted.
Around 19% of last year's extraordinarily dry conditions are attributable to human activities that promote climate change, they said.
Williams, the study's lead author, said with dry conditions likely to persist, it would take multiple wet years to remediate their effects.
"It's extremely unlikely that this drought can be ended in one wet year," he said in a release.
By analyzing tree ring patterns, which provide insights about soil moisture levels each year over long timespans, the scientists studied the area from southern Montana to northern Mexico, and from the Pacific Ocean to the Rocky Mountains.
They discovered that megadroughts occurred repeatedly in the region from A.D. 800 to 1600 with dramatic shifts in dryness and water availability happening long before the onset of human-caused climate change beginning in the 20th century.
However, climate change has played a major role in the severity of the cycles since then and is responsible for about 42% of the soil moisture deficit since 2000, the paper found.
"Without climate change, the past 22 years would have probably still been the driest period in 300 years," Williams said. "But it wouldn't be holding a candle to the megadroughts of the 1500s, 1200s or 1100s."