Nearly 1,000 years ago, a megadrought ravaged the southwestern U.S., swiftly wiping out a thriving indigenous culture and rendering once-arid land unusable. Scientists have long warned that the climate crisis may trigger another megadrought. And according to a new study, that megadrought isn’t just on its way—it’s likely already under way, and it could be worse than anything the region has ever seen.
The research, published in the journal of Science on Tuesday, is based on modern weather observations, 1,200 years of tree-ring data, and dozens of climate models. It is the most up-to-date and comprehensive long-term climate analysis of the region.
The study found that the extreme dry spell could hit a huge region of the West from Oregon and Montana, down through California and New Mexico, and part of northern Mexico. A leading cause of the increasingly dry conditions is the climate crisis. A warmer world creates the conditions for more severe, longer, and more widespread drought.
“The West gets drier when the world gets warmer,” Park Williams, a tree ring expert at Lamont-Doherty Earth Observatory who led the study, told Earther in an email.
The effects of this emerging megadrought are already on display. Recent research shows that parts of the Colorado River—which 40 million people depend on for drinking water—is drying up. Forests are drying out, becoming infested with destructive insect outbreaks as warmer winters allow them to thrive. That’s led to more frequent wildfires in California and the western U.S. at large. And as a result, people and ecosystems are suffering.
The researchers observed the growth rings of thousands of trees throughout the West to reconstruct rainfall patterns since 800. They found that the four major decades-long megadroughts that affected the area all occurred before the mid 17th century. Since then, there have been other droughts, but none came close to those—until now.
By comparing data on those ancient megadroughts with soil moisture data from 2000 to 2018, the team found that the megadrought the region is currently experiencing may actually be the most severe the area has ever seen, and that its affecting the largest area of any megadrought in recorded history over the past 1,200 years. With the risk of drought rising into the coming decades, policymakers need to begin preparing now.
“Let’s plan for less water and more severe droughts now so that we don’t need to dramatically and painfully adjust all at once when crisis hits,” he said.
As proof that the U.S. is capable of those adjustments, he said, we can look to its response to the current pandemic.
“We can learn from the coronavirus in this case,” he said. “With that virus, we’ve been faced with the embarrassing realisation that we’ve been ignoring experts for decades by not preparing, but also that U.S. citizens are quite capable of acting on scientific projections even in the face of uncertainty.”