From Inside Climate News (Bob Berwyn):
Low-elevation snowpack across the Rocky Mountains, the Sierra Nevada and the Cascades will disappear in the coming decades if global warming continues unabated, according to a new study. The changes will cause water shortages in the region and dry out forests and grasslands, the study’s authors say.
According to the research, the snow line—the altitude above which it snows, and below which it rains—will climb as much as 800 feet in the Colorado Rockies, and 1,400 feet in the Rockies of Idaho and Wyoming by 2100 if greenhouse gas emissions continue at the current rate. The snow line will rise by an average of 950 feet across six Western mountain regions by century’s end. The study, by a team of University of Utah scientists, was published online in the journal Geophysical Research Letters last month.
A shift of that magnitude means less spring runoff for millions of square miles of watersheds in the lower elevations of the West. The melting of the spring snowpack determines how much water feeds critical reservoirs in 11 Western states. That water helps sustain Phoenix, Los Angeles, Las Vegas and other cities, as well as farms and mountain ecosystems, through hot, dry summers.
Less spring snowpack means water managers will have to capture runoff earlier in the season, and dried up forests, brush and grasslands will increase early season wildfires. Western ski resorts will also be affected, because the snowline will rise above the base elevation of many of them, according to the study.
“We identified an elevation threshold above which precipitation is the main driver of springtime snowpack,” said University of Utah climate researcher Court Strong, who led the study. Right now, that line is at about 6,500 feet but it will rapidly march up the mountain during the coming decades if global warming continues unchecked, Strong said.
Along with melting Arctic ice and vanishing glaciers worldwide, declining snow cover is a powerful gauge of global warming impacts, researchers say.
“Snowpack is one of the most pure forms of a climate indicator,” said John Abatzoglou, a University of Idaho geography professor who studies climate impacts but was not involved in the study. “We can see our snowpack, we can see when it decreases, or moves up and down the mountain…It’s one the best independent measures when it comes to climate change.”
Climate change has already reduced snow cover in the Rockies by 20 percent since 1980, and pushed up the peak of spring runoff by as much as two weeks in parts of the Mountain West, recent studies have shown. All global climate models have projected steadily increasing temperatures, and some suggest a slight increase in precipitation for the region.