Southwest US's Alarming 'Megadrought' Could Last Until 2100

Newsweek

6 days ago

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Parts of the United States may be in a drought that will last until the end of the century, according to a concerning new study.
Analysis by researchers from the University of Texas at Austin indicates that the Southwest is facing a "megadrought" worse than any in the past 1,200 years—and it could continue until the end of the 21st century if not even longer.
The team suggest that ongoing warming could be disrupting the natural rhythm of a climate cycle known as the Pacific Decadal Oscillation (PDO), which brings drought and rains to the Southwest U.S. every 20 or 30 years. However, under certain conditions of warming, this phase can persist for far longer.
Researchers noted that in the last period of hemispheric warming, around 6,000 years ago, the PDO was forced out of rhythm, leading to a drought that lasted for millennia—and it now appears to be happening again.
A dead fish lies near a lake September 6, 2000 just outside the city of Dallas, Texas, when much of Northern Texas had dried out.
A dead fish lies near a lake September 6, 2000 just outside the city of Dallas, Texas, when much of Northern Texas had dried out.In their study, PhD student Victoria Todd and professor Timothy Shanahan analyzed sediment cores from the Rocky Mountains, and found evidence of a major drought 6,000–9,000 years ago far worse than scientists had previously assumed.
The drought was primarily caused by a drop in winter rain needed to feed major rivers, coinciding with a swell of plant growth across continents which caused the Earth to warm as it absorbed more of the sun's rays.
This triggered a shift in ocean and atmospheric patterns over the North Pacific that resembled the drought phase of the PDO, which is causing the current drought in the Southwest—except that this drought phase dominated for thousands of years.
Todd told Newsweek: "By combining new paleoclimate reconstructions and climate model simulations, we showed that moderate Northern Hemisphere warming—in the past and projected into the future—can lock North Pacific sea surface temperatures into a temperature pattern that dramatically reduces winter precipitation and drives long-term drought in the Southwest US.
"The fact that this is wintertime drought is particularly important because of the impact on snowpack in the Rockies and its role in Colorado River flow and western U.S. water resources."
The researchers examined whether this could happen again by teaming up with the University of Colorado to build climate model projections. When these results were averaged, they noted a similar response—including steady declines in winter precipitation.
Shanahan said in a statement: "If global temperatures keep rising, our models suggest the Southwest could remain in a drought-dominated regime through at least 2100.
Referencing the Colorado River, where flows have declined by 20 percent over the last century, Shanahan added: "Many people still expect the Colorado River to bounce back. But our findings suggest it may not.
"Water managers need to start planning for the possibility that this drought isn't just a rough patch—it could be the new reality."
Todd told Newsweek: "Our work […] also suggests that, while the simulations with warming produce a North Pacific response and lead to winter precipitation declines, they still underestimate the magnitude of this response.
"This suggests that it is likely we are underestimating the magnitude of future drought as well. We need to better understand why the magnitude of the precipitation response is being underestimated by models and what it means for future precipitation in the Southwest U.S."
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Reference
Todd, V. L., Shanahan, T. M., DiNezio, P. N., Klavans, J. M., Fawcett, P. J., Anderson, R. S., Jiménez-Moreno, G., LeGrande, A. N., Pausata, F. S. R., Thompson, A. J., & Zhu, J. (2025). North Pacific ocean–atmosphere responses to Holocene and future warming drive Southwest US drought. Nature Geoscience, 18(7), 646–652. https://doi.org/10.1038/s41561-025-01726-z