New study: Winter 2026’s snow drought in Upper Colorado River Basin was 14 times more likely due to climate change

At 17% of snow pillows and 20% of ERA5-Land pixels, the observed March 15 SWE was the lowest over the 1987-2026 period

Colorado’s winter 2026 snow drought wasn’t just bad luck, it was a tell of how climate change is continuing to affect the Centennial state and its river basins, according to new research from Colorado School of Mines assistant professor in the Department of Geology and Geological Engineering Adrienne Marshall.

Marshall and her team found that a snow drought as severe as the one that hit the western U.S. in spring 2026 was about 4.4 times more likely to occur in today’s climate than in the pre-industrial era.

Furthermore, the study also reported that in the Upper Colorado River Basin, the same snow drought was found to be approximately 14 times more likely because of climate change.

The study was the first to formally attribute a large-scale snow drought event to climate change using modern statistical attribution methods. These same techniques have been used by scientists for years to link individual heat waves and floods to warming, now applied to snowpack.

The peer-reviewed study was published in the Proceedings of the National Academy of Sciences.

Raw data from winter 2026’s snow drought

Researchers said statewide snow water equivalent (SWE) bottomed out at levels not seen since official record-keeping began in winter 1986/87.

“At 17% of snow pillows and 20% of ERA5-Land pixels, the observed March 15 SWE was the lowest over the 1987-2026 period,” the study said. “It was at or below the 10th percentile for 45% of snow pillows and 50% of pixels. Over the 77-y period of record in ERA5-Land volumetric SWE was low, although not record-breaking, in all spatial domains.”

Western US SWE volume was about 40 km³ lower or 25% smaller than an event with a comparable return interval in 1850-1900.

The study also said that across the western United States, the 2026 snow drought had a 6.8-year return interval, with respect to the current climatology based on the downscaled climate data.

Furthermore, the study also said the snow drought had a 30-year return interval, with respect to the 1850-1900 counterfactual period.

The 1850–1900 counterfactual period is a baseline timeframe used in climate science and represents a pre-industrial ‘world that might have been’ without modern human-caused greenhouse gas emissions, according to the National Academies.

The study said the figures result in a median risk ratio (RR) of 4.4, meaning the 2026 snow drought was approximately four times more likely in current climatology than in 1850-1900.

Marshall’s insight on the snow drought

Marshall said in a July 20 Colorado School of Mines article that the researchers found that the amount of “missing” snow associated with climate change was significant.

“Across the western United States, the water stored in the form of mountain snowpack during the 2026 event was approximately 40 cubic kilometers lower than would be expected from a similarly rare event in a pre-industrial climate,” she said. 

Marshall noted the study also examined how the likelihood of similar snow droughts could change in coming decades under a moderately high greenhouse gas emissions scenario.

“Today, a snow drought as severe as the 2026 event has roughly a 10% chance of occurring in any given year across the western United States,” she said. “By the 2050s, that probability is projected to more than triple, reaching 32% in a scenario with moderately high greenhouse gas emissions.”

Marshall said the chances of a severe snow drought by century’s end are even worse.

“By the 2090s, the probability rises to 87%, meaning that snow conditions comparable to those observed in 2026 would become more common than not.”

The Upper Colorado River Basin was found to also experience substantial declines in snowpack as the climate warms, however, Marshall said an event as extreme as the 2026 snow drought remained relatively uncommon even by late century.

The researchers estimated the annual probability of a comparable event in the basin would increase from about 0.02% today to 2.1% by the 2050s and 17% by the 2090s.

“One of the goals of climate attribution science is to help people understand future risks through events they have already experienced,” Marshall said. “The 2026 snow drought provides a tangible example of what the future would look like if greenhouse gas emissions continue to rise. At the same time, these outcomes are not inevitable. Lower emissions would reduce the risk.”