The California Aqueduct and Interstate 5 converge near Gustine, California, the US. Photo: VCG
The megadrought that has parched southwestern US and parts of Mexico over the last two decades is the worst to hit the region in at least 1,200 years, researchers said Monday.
Human-caused global heating accounts for more than 40 percent of the dry spell’s intensity, they reported in the journal Nature Climate Change.
“The turn-of-the-21st-century drought would not be on a megadrought trajectory without anthropogenic climate change,” lead author Park Williams, an associate professor at the University of California in Los Angeles, and colleagues wrote.
Over the last decade, California and other western states have experienced severe water shortages, triggering periodic restrictions on water usage.
Occasional heavy snow or rainfall have not been enough to compensate.
2021 was especially dry. As of Thursday, 95 percent of western US had drought conditions, according to the US government’s Drought Monitor.
In summer 2021, two of North America’s largest reservoirs – Lake Mead and Lake Powell – reached their lowest recorded level in more than a century.
The odds are high that the current dry spell will continue for at least a couple of years, according to the findings.
Running simulations based on soil moisture records stretching back 1,200 years, the researchers calculated a 94 percent chance that the drought would extend through 2022.
There’s a three-in-four chance it will run until the end of the decade.
Tree-ring analysis shows that the area west of the Rocky Mountains from southern Montana to northern Mexico was hit repeatedly by so-called megadroughts – lasting at least 19 years – between the years 800 and 1600.
Earlier research had established that the period 2000-18 was likely the second worst drought since the year 800, topped by one in the late 1500s.
Data from 2019-21, backed by new climate models released in 2021, have revealed the current drought to be worse than any from the Middle Ages.
But without climate change it “wouldn’t hold a candle to the megadroughts of the 1500s, 1200s or 1100s,” Williams said.