Will El Niño ride to the Colorado River’s rescue?

Maybe, but don’t count on it. But have you heard the latest on the Pacific Decadal Oscillation? Not good!

by Allen Best

Twenty years ago, some might have hoped that drought in the Colorado River Basin would diminish or disappear altogether.

Hope remains but of a distinctly diminished variety. Will the arriving El Niño will bring a rare deluge, bringing the water levels of Lake Powell from the brink of deadpool, too low to release water downstream?

Two books have been written in the last few years with “deadpool” in their titles, indicating how close to the edge we have been. If not for a very big snow year in 2022-2023, we might well have been there in 2023. Now, we’re in the same place or worse.

It’s very possible that Lake Powell will have too little water by September to generate electricity. That is called minimum power pool. Deadpool lies just a few steps below.

Unlike 20 years ago, nobody seems to harbor delusions that this problem will be solved by a turn of nature. As for the El Niño, it may help but Brad Udall advised against too much hope hedging.

Speaking at the Colorado River conference at the University of Colorado Law School in early June, Udall explained that El Niño increased the odds of large impacts as it did in 1983. That year Glen Canyon Dam almost broke with the runoff of 24 million acre-feet. Another big year was 1997 with 19 million acre-feet. And then 1016 produced 13.4 million in 2016. Those exceptional years aside, El Niño can be sort of a bust, said Udall, a scientist and scholar affiliated with Colorado State University.

The evidence continues to strengthen that the warming climate — a climate caused by growing greenhouse gas emissions — will continue to rob the river of water. And, as in the past few decades, the warm temperatures will filch water at larger and large volumes.

Udall had been tasked with summarizing what the 2026 water year that ends in September could be in the context of long-term trends and short-term impacts.

NOAA’s Colorado River Basin Forecast Center had predicted 13% of average runoff flows, just 800,000 acre-feet, compared to the more average 6 million. “It’s below even 2002, which was the lowest year on record, just about a million,” said Udall.

As is now widely understood, those who met in Santa Fe in November 1922 to create a framework for sharing the Colorado River had assumed river flows from the upper basin states would be plentiful, 17.5 to 18 million acre-feet. They erred grievously on the side of optimism. The 20^th century average was 15.2 million acre-feet, and this century bent downward even more. Since 2019, the average has been 10.2 million acre-feet.

Realizing how on-target climate change models have been both comforting and chilling, consider a chapter by the late John Opie, the author of several books about the Ogallala Aquifer. In his concluding chapter in a book published in 1998 called “Sense of he American West,” he mentioned predictions that global temperatures would rise1.5 degrees C by 2030. So far, we’re at 1.2 to 1.35 degrees C.

In the American Southwest, we’re heating more rapidly, about 3.5 degrees C per century, according to a paper issued by the Rhodium Group.

We had a sharp taste of that in March. Temperatures across the Colorado River Basin that month averaged 9 degrees F above the 20^th century average. In Colorado, Fort Collins had a new record for the first day above 90 degrees in records going back to 1895. This year that first 90-degree day arrived in March. This year’s first skipped over April. The previous earliest was in May.

What will increased heat mean in terms of precipitation? The short answer is that it increases evaporation and transpiration. So, of the snow or rain that falls, less of it emerges as water in downstream reservoirs or, for that matter, in transmountain diversions.

Taking a more global perspective, Udall pointed to a natural phenomenon that became apparent to scientists only in 1997, called the Pacific Decadal Oscillation. It alters jet streams and storm tracks in the American West. Like El Niño and La Nina, it has different phases. The negative phase of the Pacific Decadal Oscillator pushes storm tracks north, meaning drier conditions in the Colorado River Basin.

Now it seems stuck, according to a paper issued by scientists in 2025. The scientists claim this trend is largely driven by human emissions of aerosols. They cooled the planet, but as we cease their emissions, the effect is to warm the planet. The takeaway from that paper is as long as greenhouse gas emission trends continue, the Pacific Decadal Oscillation will remain stuck, producing drought in the Southwestern states.

Another recent paper examined the North Pacific Ocean and the response to changes in the atmosphere during the last 6,000 years. The takeaway is that the models had under-appreciated the effect of warming, which causes 20% precipitation reductions.

“And I’ll note a 20% decline in precipitation is probably like a 50% decline in river flow,” said Udall.

In other words, 90% of the heat caused by the thickening concentration of greenhouse gases in the atmosphere goes into the ocean, and scientists are still piecing together how that heat in the ocean then affects the climate for the Colorado River Basin.

Even if we reduced our greenhouse gas emissions immediately, the heat will remain for hundreds and then thousands of years.

Think we might see a return to even the 15.2 million acre-feet of the 20^th century at Lee Ferry? Forget about it. We might get lucky with an El Niño, but then again, said Udall, the evidence doesn’t support much optimism. The more grounded hope is that the meager snowfall and extraordinary warmth of the last year does not come with an echo this coming winter.