WATER SECURITYClimate Models Reveal How Human Activity May Be Locking the Southwest into Permanent Drought
A new wave of climate research is sounding a stark warning: Human activity may be driving drought more intensely –and more directly –than previously understood. One example: The southwestern United States has been in a historic megadrought for much of the past two decades, with its reservoirs including lakes Mead and Powell dipping to record lows and legal disputes erupting over rights to use water from the Colorado Rive.
A new wave of climate research is sounding a stark warning: Human activity may be driving drought more intensely – and more directly – than previously understood.
The southwestern United States has been in a historic megadrought for much of the past two decades, with its reservoirs including lakes Mead and Powell dipping to record lows and legal disputes erupting over rights to use water from the Colorado River.
This drought has been linked to the Pacific Decadal Oscillation, a climate pattern that swings between wet and dry phases every few decades. Since a phase change in the early 2000s, the region has endured a dry spell of epic proportions.
The PDO was thought to be a natural phenomenon, governed by unpredictable natural ocean and atmosphere fluctuations. But new research published in the journal Nature suggests that’s no longer the case.
Working with hundreds of climate model simulations, our team of atmosphere, earth and ocean scientists found that the PDO is now being strongly influenced by human factors and has been since the 1950s. It should have oscillated to a wetter phase by now, but instead it has been stuck. Our results suggest that drought could become the new normal for the region unless human-driven warming is halted.
The Science of a Drying World
For decades, scientists have relied on a basic physical principle to predict rainfall trends: Warmer air holds more moisture. In a warming world, this means wet areas are likely to get wetter, while dry regions become drier. In dry areas, as temperatures rise, more moisture is pulled from soils and transported away from these arid regions, intensifying droughts.
While most climate models simulate this general pattern, they often underestimate its full extent, particularly over land areas.
Yet countries are already experiencing drought emerging as one of the most immediate and severe consequences of climate change. Understanding what’s ahead is essential, to know how long these droughts will last and because severe droughts can have sweeping affects on ecosystems, economies and global food security.
Human Fingerprints on Megadroughts
Simulating rainfall is one of the greatest challenges in climate science. It depends on a complex interplay between large-scale wind patterns and small-scale processes such as cloud formation.
