The Ocean Is Talking. Is the Desert Listening?
The tropical Pacific has always set the rules for desert water. Climate change is rewriting them.
The ocean is the desert’s thermostat, even from hundreds of miles away. The same tropical Pacific temperatures that drive El Niño and La Niña determine how much water falls on the Rockies, how full Lake Mead gets, and whether the Colorado River has enough left over to reach the sea. This summer, the Pacific is sending a complicated message.
El Niño, La Niña, and the Desert’s Water Supply
El Niño and La Niña are opposite phases of the same climate pattern: ENSO, the El Niño-Southern Oscillation, driven by temperature swings in the tropical Pacific. Normally, trade winds push warm water westward across the equatorial Pacific, piling it up near Australia and Papua New Guinea. When those winds weaken or reverse, that warm water sloshes back east, rewiring global weather patterns from the top of the atmosphere down. That’s El Niño. When sea surface temperatures in that same equatorial band run cooler than normal, you get La Niña. The cycle shifts every few years, and the effects ripple across the globe.
For the desert Southwest, no climate pattern matters more. La Niña raises the odds of below-average precipitation by more than 50% during the cool season, with California, Nevada, Arizona, and Utah among the most consistently affected states. El Niño reverses that signal: warmer Pacific waters push winter storm tracks south, bringing more rain and snow to the region and crucially, the kind of snowpack that fills reservoirs. The 1997–98 El Niño drenched Southern California. Five of the last six winters brought La Niña conditions instead, which goes a long way toward explaining the persistent drought that defined the first half of this decade. That’s not a run of bad luck. That’s a pattern.
Climate change is now shifting the baseline those odds are measured against. El Niño probability currently sits at 82% for May-July 2026, rising to 96% through winter 2026-27 (Source: NOAA Alert, May 14, 2026). For the Southwest, a strong El Niño winter typically means above-average precipitation across Arizona, New Mexico, and Southern California. Whether a warming ocean delivers that outcome as reliably as it once did is the open question. What those odds mean for actual water availability is increasingly shaped by something bigger than ENSO: the warming of the ocean itself.
El Niño and La Niña explained in this video from NASA’s Scientific Visualization Studio
The Ocean Is Absorbing More Than We Realize
The ocean is the engine behind that shift. The UN notes that the ocean absorbs roughly 90% of the excess heat generated by rising greenhouse gas emissions, which is why global sea surface temperatures jumped to record levels in 2023 and 2024 and have remained near those records throughout 2025. That heat doesn’t stay put. NOAA has documented that under increased greenhouse gas forcing, the upper layers of the tropical Pacific warm faster than the deeper ocean, strengthening the very feedbacks that drive El Niño and La Niña in the first place.
The ocean isn’t warming on its own. It’s absorbing the heat we’ve pumped into the atmosphere by burning coal, oil, and gas — and in doing so, it’s altering the climate patterns the Southwest has long depended on to forecast its water future.
This past March made the argument in real time. A high-pressure system trapping heat from unusually warm Pacific waters drove temperatures across the desert Southwest against the backdrop of the warmest winter on record and significant drought. Nationally, the scale was hard to ignore: between March 16–23, over 1,500 daily high temperature records fell, 660 of them all-time March records.
The Colorado River Listens to the Ocean
What happens in the tropical Pacific doesn’t stay there and nowhere is that clearer than in the Colorado River basin.
Despite originating in the landlocked Rockies, the Colorado’s water supply is, it turns out, readable from the ocean. A 2020 study by researchers at Utah State University, published in Communications Earth & Environment, found that severe water shortages on the Colorado can be forecast several years in advance simply by tracking sea surface temperatures in three ocean regions: a cooling tropical Pacific, a warming North Pacific, and a warming southern tropical Atlantic. The river’s fate is written in the ocean before it ever shows up in a reservoir gauge.
The paleoclimate record makes the long-term stakes harder to ignore. Research published in Paleoceanography and Paleoclimatology reconstructed climate conditions in the Great Basin going back thousands of years and confirmed a dry period lasting roughly from 9,800 to 5,400 years ago, triggered by a warming Pacific and shrinking Arctic sea ice. The researchers concluded that the same ocean conditions driving that ancient aridification are now reasserting themselves, this time pushed by greenhouse gas emissions rather than orbital shifts. Their finding carries a sobering implication: the true worst-case scenario for the Southwest may not be the Medieval megadrought that water managers have long used as their planning benchmark, but the multi-millennia dry stretch that came before it.
Some scientists now prefer the term aridification over drought for what’s unfolding in the Southwest, because drought implies something temporary. What the ocean record suggests, amplified by warming, looks less like a dry spell and more like a fundamental reset of baseline conditions.
What This Summer Holds for the Desert
Drought is expected to persist across much of the West through mid-year, NOAA’s spring outlook is unambiguous on that point. The summer will be hot and dry across the interior West regardless of El Niño, whose wetter effects on the Southwest won’t arrive until late fall at the earliest.
The one summer wildcard is the monsoon. Forecasters at Climate Impact Company project a stronger-than-normal Southwest monsoon beginning as early as June, with Gulf moisture pushing north into Arizona, New Mexico, and Colorado. The intense heat already building across the region may reinforce that signal, deepening the low-pressure system that draws monsoon moisture inland.
But monsoon rain isn’t snowpack. It falls hard, drains fast, and often evaporates before it reaches a reservoir. Even a strong monsoon wouldn’t make a meaningful dent in years of accumulated deficit.
The real question is winter and whether El Niño, now projected at 96% probability through early 2027, delivers what the Pacific occasionally promises. One good wet season would be a reprieve. It wouldn’t be a solution.
The Ocean Belongs to the Desert Too
The ocean has always governed life in the desert Southwest, even when it was easy to forget. The Colorado River’s water budget is set in the Pacific. The monsoon’s strength is negotiated in the Gulf. The winter snowpack that fills reservoirs is delivered by storm tracks the ocean steers. None of that is new, but the consequences of ignoring it are.
Protecting the ocean isn’t just a coastal concern. For anyone living in the desert Southwest, it’s a water issue.
Sources
ENSO Probability Forecast NOAA Climate Prediction Center, El Niño/La Niña Advisory, May 14, 2026 https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml
Temperature Records, March 2026 Climate Central
https://www.climatecentral.org
Global Ocean Surface Temperatures Climate Central / Observable https://observablehq.com/@climatecentral/daily-sst
Ocean Heat Absorption United Nations Climate Action https://www.un.org/en/climatechange/science/climate-issues/ocean
Tropical Pacific Warming and ENSO Feedbacks NOAA
https://www.noaa.gov
Chikamoto, Y., Wang, SY.S., Yost, M. et al. Colorado River water supply is predictable on multi-year timescales owing to long-term ocean memory. Commun Earth Environ 1, 26 (2020). https://doi.org/10.1038/s43247-020-00027-0
Matthew S. Lachniet, Yemane Asmerom, Victor Polyak, Rhawn Denniston. Great Basin Paleoclimate and Aridity Linked to Arctic Warming and Tropical Pacific Sea Surface Temperatures. (2020). https://doi.org/10.1029/2019PA003785
Southwest Drought Outlook NOAA Spring 2026 Drought Outlook
https://www.cpc.ncep.noaa.gov
Southwest Monsoon Forecast Climate Impact Company, U.S. Month 1–4 Ahead Climate Outlook, Summer 2026 https://climateimpactcompany.com/u-s-month-1-4-ahead-climate-outlook-summer-2026-features-dangerous-northwest-west-heat-and-dryness-but-a-stronger-than-normal-southwest-u-s-wet-monsoon-2-2/