Water resources will fluctuate increasingly and become more and more difficult to predict in snow-dominated regions across the Northern Hemisphere by later this century, according to a comprehensive new climate change study led by the National Center for Atmospheric Research (NCAR) and co-authored by a Cornell climate scientist.

Flavio Lehner, assistant professor of earth and atmospheric sciences in the College of Agriculture and Life Sciences, and the research team found that, even in regions that keep receiving about the same amount of precipitation, streamflow will become more variable and unpredictable. As snowpack recedes in a warmer future and fails to provide reliable runoff, the amount and timing of water resources will become increasingly reliant on periodic episodes of rain.

“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,” said NCAR scientist Will Wieder, the lead author. “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.”

Many regions of Earth rely on the accumulation of snow during the winter and subsequent melting in the spring and summer for regulating runoff and streamflow. Observations show that snowpack is already melting earlier, even declining in many regions. This decline will become so pronounced toward the end of the century that the amount of water contained in snowpack at the end of an average winter in parts of the U.S. Rocky Mountains could plummet by nearly 80%, the scientists found.

The changes in runoff and streamflow are likely to have cascading impacts on ecosystems that depend on reliable water from snow, the study warns. Although the changes won’t be uniform across regions, more snow-free days and longer growing seasons will put stress on water resources, drying out soils in many areas and heightening fire risk.

The scientists, assuming emissions of greenhouse gases continue at a high rate, drew on an advanced set of computer simulations to fill in details about the future of water resources, showing the extent to which changes in temperature and precipitation will alter snow accumulation and runoff patterns in the Northern Hemisphere. Although past research looked at the impacts of climate change on water availability, the new study focuses on the increasing variability of water resources.

The results illuminate the extent to which widespread shifts in the timing and extent of water flows will occur in much of the world by 2100. There will be an average of about 45 more snow-free days yearly in the Northern Hemisphere, assuming high greenhouse gas emissions. The largest increases will occur in midlatitudes that are relatively warm and high-latitude maritime regions that are influenced by changes in sea ice.

Many regions that rely the most on predictable relationships between snowpack and runoff will experience the largest loss in predictability because of a sharp decline in reliable episodes of spring runoff. These regions include the Rocky Mountains, Canadian Arctic, eastern North America and Eastern Europe. The authors warn that this will substantially complicate the management of freshwater resources, both for society and ecosystems.

“We are in a race with predictability when it comes to streamflow because we’re trying to improve our forecasts through better data, models and physical understanding, but these efforts are being canceled by the rapid disappearance of our best predictor: snow,” said Lehner. “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.”

The study was published July 18, 2022 in the Proceedings of the National Academy of Sciences and was funded by the National Science Foundation, which is NCAR’s sponsor.