A Megadrought Has Been Plaguing the U.S. for 27 Years—And Scientists Say It May Never End

3 min readHere’s what you’ll learn when you read this story:The climate of the American Southwest is driven in large part by the El Niño–Southern Oscillation and the Pacific Decadal Oscillation (PDO).While many experts assumed the PDO was cyclical, new studies have found that anthropogenic climate change could “lock” the PDO in a negative phase, drying out the Southwest.It’s possible that the upcoming “very strong” El Niño could knock the PDO into a positive phase, but scientists warn that the region will remain in a long-term process of aridification.On September 10, 2026, satellite images from the NASA-USGS Landsat 8 captured the stunning consequences of the 25-year-long megadrought that has gripped the southwestern United States. Lake Powell, the serpentine reservoir formed by Glen Canyon dam that stretches across the border of Utah and Arizona, appears like a small trickle compared to its previous stature as one of the country’s largest man-made lakes. Today, the water’s surface stands at a record low 3,517.24 feet, only 30 feet from “minimum power pool” (when the dam no longer produces hydropower). It seems almost impossible that a little more than 40 years ago, Lake Powell overflowed with too much water.That’s because the weather in the southwest is historically dominated by two climactic phenomena off the Pacific Ocean—the El Niño–Southern Oscillation and the Pacific Decadal Oscillation (PDO). Most of us are familiar with the El Niño/La Niña cycles, which cause an alternation between warm, dry conditions and cold, moist conditions every two to seven years. However, the PDO is a more long-lived phenomenon, waxing and waning (as its name suggests) every couple decades. This cycle flows between a “warm/positive” phase and “cool/negative” phase with areas of cooler or warmer sea surface temperatures (SSTs) moving back and forth in the Pacific Ocean.During the warm phase of the PDO, a complex interaction with SSTs and atmospheric conditions essentially pushes wet weather over the Southwest. Lake Powell flooded in 1983, at the peak of a warm phase that made it the Southwest’s wettest period in a millennium. Then, things changed, as the PDO entered a cool phase and forced jet streams to the north, leaving the Southwest high and dry—and that’s how things have stayed for nearly 30 years. With the governors of some Western states literally praying for rain, the hope is that the PDO will soon switch course and offer some much-needed relief. Unfortunately, some scientists think that hope might be misplaced.A study published in the journal Nature in July 2025 found that human activity greatly influenced the cyclical nature of the PDO within the past several decades. Industrial aerosol emissions coerced the PDO into a positive trend from the 1950s until the 1980s, while a drop-off of these emissions combined with increased greenhouse gasses pushed the PDO in the other direction. “We project that so long as ongoing anthropogenic forcing trends continue, the PDO will remain persistent in its negative state,” the authors finally conclude.In other words, those prayers will remain unanswered.However, one thing could tip the climatic scales in a more favorable direction for the region. All scientific signs point to a “very strong” El Niño arriving this fall that could push the PDO into a warm phase, according to Science News. But even if the Southwest is graced with a wetter-than-average winter, it’s still unlikely to end the megadrought and the West’s ongoing water crisis, especially because a lot more moisture will need to seep into the extra parched soil in the mountains before running off into the critical reservoirs that provide water for tens of millions of people.“Even the best-case scenario with a warm tropical Pacific, cool tropical North Atlantic, and cold tongue warming will not lift cool season precipitation and summer soil moisture back to the levels of the late 20th century,” a 2025 study in the journal npj Climate and Atmospheric Science reported. “The long-predicted aridification of the American Southwest is underway and fortuitous decadal climate variability will be insufficient to stop it.”Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.