Water resources will fluctuate increasingly and become more difficult to predict in snow-dominated regions.
Record temperatures during heatwaves in Europe have caused water shortages in parts of Italy and other nations, but there is even worse news: such shortages are set to become more common in coming decades as water sources get increasingly stressed by warming temperatures, scientists warn.
“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,” says a team of scientists at the National Center for Atmospheric Research (NCAR), who conducted a study on the effects of climate change on water sources in snow-dominated regions.
Troublingly, even in regions that will continue having around the same degree of precipitation in future, streamflow will fluctuate unpredictably because receding snowpack will lead to less reliable runoff. As a result, water resources will become more and more reliant on periodic rainfall.
“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,” explains Will Wieder, a scientist who was the lead author of the study.
“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,” he adds.
Already snowpack is melting earlier every year than in the past, and its extent has been on the decline in many regions. By the end of the century the amount of water contained in snowpack after an average winter in parts of the Rocky Mountains in the United States, for instance, could plummet by nearly 80%.
Such drastic reductions in runoff and streamflow will have “cascading impacts on ecosystems that depend on reliable water from snow,” the scientists note. “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.”
Many regions worldwide rely on snow accumulated during winter and melting in the spring and summer for regulating runoff and streamflow. However, snowpack in many regions are becoming thinner and melting earlier because more precipitation during winter months falls as rain rather than as snow owing to warming tenperatures. This can cause snow to melt during winter instead of spring.
By the end of the century, the scientists have found, there will be an average of about 45 more snow-free days each year in the Northern Hemisphere if we continue pumping greenhouse gases at the current rate into the armosphere. The worst-affected will be relatively warm regions at mid-latitudes as well as high-latitude maritime regions that are influenced by seasonal 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 pulses of spring runoff,” the scientists write. “These regions include the Rocky Mountains, Canadian Arctic, Eastern North America, and Eastern Europe.”
These changes will greatly complicate freshwater resource management systems, they warn.
“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,” stresses Flavio Lehner, a professor of earth and atmospheric science at Cornell University who was a co-author of the study.
“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 adds.