Is the Drought in the Southwest Permanent?

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A.Reservoirs along the Colorado River, among the nation’s most important water supplies, are dwindling by the day, exposing sunken boats, spilled bodies and barren soil. It’s just the latest phase of a drought that has crushed the Southwest over the past two and a half decades: the driest period the region has seen in 1,200 years. Even the torrential rains from atmospheric rivers that have swept across the Southwest in recent winters have done little to alleviate this trend.

It looks like the drought is here to stay for many more years. In fact, the current drought could last another two decades, according to a recently published article in Nature. The results of their analysis, which draw on data from more than 500 climate simulations produced by world-renowned research institutions, rewrite our understanding of one of the major climate systems controlling the weather in the western United States.

The Pacific Decadal Oscillation, or PDO, is a fluctuating pattern of warm and cold sea surface temperatures in the North Pacific that shapes precipitation trends on both sides of the ocean. Much like El Niño/Southern Oscillation, the PDO has historically moved between so-called positive and negative phases, with precipitation increasing in the western United States when positive and decreasing when negative. Since the PDO was first described in the 1990s, scientists have assumed that any changes in the index are driven by the natural variability of the climate cycle and completely independent of global warming and humanity’s various pollutants.

The prevailing wisdom no longer made sense.

But this assumption makes it difficult to describe the recent behavior of the climate model. Since the late 1990s, with the exception of a few odd years, the PDO has been consistently negative, according to data maintained by the National Oceanic and Atmospheric Administration. “And July was the most negative month in history,” said Jeremy Klavans, a climatologist at the University of Colorado, and lead author of the recent paper.

Klavans and his colleagues wanted to untangle what was driving this negative trend since the prevailing wisdom no longer made sense. According to conventional explanations, random fluctuations should have tilted the PDO toward the positive, pushing ocean surface temperatures toward a warmer-than-normal phase. Instead, aside from a few brief rises, it has spent nearly 30 years “stuck” in negative territory, or colder than “normal.” “The only way to get stuck, if you think ODP is driven by natural phenomena, is to have really extreme luck,” he said. Maybe there’s something else at play, he thought.

To identify what that might be, the team collected data from 572 different simulations across 12 different state-of-the-art climate models, then calculated the average PDO index over time for all simulations. Although climate models cover a very wide range of outcomes, the average aligns closely with what happened in reality, which Klavans says “is totally unexpected.” If PDO fluctuations were completely natural as most have believed so far, this correlation should not exist. When these simulations were averaged together, the natural variability canceled out, leaving only one common factor: carbon emissions and climate change.

A drought lasting another two decades or more becomes the most likely possibility.

Klavans estimates that the results show that human impacts on climate are responsible for about half of all the variability in PDO from decade to decade. This includes both the increase in greenhouse gases that have warmed the atmosphere and the decrease in aerosols – tiny particles of dust, smoke, salt and sulfur often emitted by heavy industries – which have had a cooling effect until recently. “If these two things continue to happen at the same time, aerosol reduction and greenhouse gas forcing, we expect the PDO to continue on its negative trend.”

“It’s a very well done job,” said Young-Oh Kwon, a climatologist at the Wood Holes Institute of Oceanography, who was not involved in the research. “It definitely changes our view of what the Pacific Decadal Oscillation is.” Scientists can no longer view the PDO and associated phenomena like El Niño or the North Atlantic Oscillation as purely natural phenomena, as they have for decades; they must consider the pronounced influence of human emissions on these regional climate patterns and how this, in turn, shapes the range of possible climate futures that people can expect.

This new vision provides a better understanding of what the future holds for the Western United States. Under conventional assumptions, precipitation projections varied greatly for the region. Some predicted the drought would end; others suggest it will deepen. But when models are modified to align with Klavans’ findings, the PDO’s sensitivity to climate change increases and the range of precipitation projections narrows. A drought lasting another two decades or more becomes the most likely possibility. And while these prospects are far from encouraging, the results ultimately give policymakers and water resource managers the ability to better plan for what the future holds.

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Main image: Lisa Parsons / Shutterstock

• Syris Valentin

  Published on December 3, 2025

  Syris Valentine is an independent essayist and journalist focused on climate and social justice. Apart from his newsletter “Just Progress”, his work has appeared in The Atlantic, Scientific American, Grist, and elsewhere.