Climate change will make Rocky Mountain water resources more volatile: study

Water resources will become more difficult to predict in the Northern Hemisphere’s snow-dominated regions later this century due to the impacts of climate change, a new study has found.

As snow accumulation recedes and fails to generate reliable runoff, the amount and timing of water resources in areas such as the Rocky Mountains will increasingly depend on rainfall, according to the study, published in the Proceedings of the National Academy of Sciences on Monday.

And even in regions that continue to receive the same amount of precipitation, streamflow will become more variable and erratic, the authors determined. 

“Water managers will be at the whim of individual precipitation events instead of having four-to-six months lead time to anticipate snowmelt and runoff,” lead author William Wieder, a scientist at the National Center for Atmospheric Research, said in a statement.

“Water management systems in snow-dominated regions are based on the predictability of snowpack and runoff, and much of that predictability could go away with climate change,” Wieder added. 

Snowpack — the layers of packed snow that typically melt and trickle down mountains during warmer months — is melting earlier than usual and is even declining in some regions, the authors noted.

Toward the end of the century, they warned, this decline could become so pronounced that the amount of water contained in parts of the Rocky Mountain snowpack at the end of winter could plunge by almost 80 percent.

Mountain snowpack is a key contributor to the water cycle of the Western U.S., as the water stored in these layers throughout the winter is discharged as runoff in the spring and summer, according to the Environmental Protection Agency.

Changes in runoff and streamflow could also have knock-on effects on ecosystems that rely on water from snow, the study authors warned. And the rise in snow-free days and longer growing seasons will also put stress on water resources — drying out soil and increasing fire risk, they added.

To draw their conclusions, the scientists said they used computer simulations to fill in details about the future of water resources and demonstrate the extent to which changes in temperature and precipitation would alter snow accumulation and runoff patterns.

While past research has explored the impacts of climate change on water availability, this report is unique in that it focuses on the increasingly erratic nature of this resource, the authors explained.

By the end of the century, there will be about 45 more snow-free days annually in the Northern Hemisphere on average, assuming that greenhouse gas emissions remain high, according to the study.

The biggest increases in snow-free days are likely to occur in relatively warm midlatitude regions and in high-latitude maritime regions that are affected by changes in sea ice, the authors found.

Among the regions to experience the greatest loss in predictability will be the Rocky Mountains, the Canadian Arctic, eastern North America and Eastern Europe, according to the study. This volatility will cause considerable complications in the management of freshwater resources, the scientists warned.

Co-author Flavio Lehner, a professor of earth and atmospheric science at Cornell University, described current circumstances as “a race with predictability” as scientists try to improve their forecasts through data, modeling and physical understanding. 

“But these efforts are being canceled by the rapid disappearance of our best predictor: snow,” Lehner said.

“It might be a race we’ll lose, but we’re trying to win it, and that is why we need to study these topics,” he added.