Southwest’s megadrought now worst in at least 1,200 years, study confirms
The prolonged drought over the past two years has broken records dating back to 800 AD. Here, in the desert near Holbrook, Arizona. (Kevin Krajic/Earth Institute)
The drought that has gripped southwestern North America for the past 22 years is the region’s driest megadrought — defined as a drought lasting 20 years or more — since at least 800 years. a new study in the magazine Natural climate change.
Due to high temperatures and low precipitation in the region from summer 2020 to summer 2021, the current drought has surpassed the severity of the megadrought of the late 1500s, which was preceded by identified by the same author The driest in 1200 years.
Because dry conditions are likely to persist, it will take multiple wet years to undo the effect, said lead author of the study Parker Williams, a geographer at UCLA. “It is highly unlikely that this drought will end in a wet year,” he said.The study was co-authored by Jason Smerdon and Benjamin Cook of Columbia Climate School.
The researchers calculated the intensity of the drought by analyzing tree rings, which provided insights into long-term soil moisture levels. They confirmed their measurements by checking the results against historical climate data. Severe drought periods are characterized by a severe lack of soil moisture, an indicator that describes how much moisture the soil contains compared to normal saturation.
Since 2000, the average soil moisture deficit has been twice as severe as any drought in the 1900s, and even worse than the driest part of the worst megadrought of the past 12th century, according to the authors.
Studying the region from southern Montana to northern Mexico, and from the Pacific Ocean to the Rocky Mountains, the researchers found that the region experienced repeated major droughts from 800 to 1600. Williams said the finding shows that water availability in the Southwest changed dramatically long before the effects of human-caused climate change in the 20th century became apparent.
Existing climate models suggest that even without climate change, the current drought would be severe, but to varying degrees. The paper found that human-caused climate change has contributed to about 42 percent of soil moisture deficits since 2000.
A major reason climate change is causing more severe droughts is that warmer temperatures are increasing evaporation, which dries out soil and vegetation. From 2000 to 2021, the temperature in the region was 0.91 degrees Celsius (1.64 degrees Fahrenheit) warmer than the average temperature from 1950 to 1999.
“Without climate change, the past 22 years could still have been the driest period in 300 years,” Williams said. “But it won’t compare to the megadroughts of the 1500s, 1200s or 1100s.”
As of February 10, according to U.S. Drought Monitor, Ninety-five percent of the western United States is experiencing drought. In the summer of 2021, North America’s two largest reservoirs on the Colorado River — Lake Mead and Lake Powell — reached their lowest recorded water levels since tracking began, according to the U.S. Bureau of Reclamation.
Regulators continue to implement water conservation measures to combat water shortages caused by drought. In August, federal officials cut water allocations to several southwestern states in response to low water levels in the Colorado River. In October, California Gov. Gavin Newsom declared a drought emergency and asked Californians to voluntarily reduce water use by 15 percent.
These moves will help in the short term, but as climate change continues to exacerbate drought conditions, conservation efforts must go beyond dry periods to help ensure people get the water they need, Williams said.
Adapted from a UCLA press release.
