Global warming may melt away fun, study says

Global warming over the next 40 years could severely reduce snowpack at Northwest ski resorts and eat into summertime water supplies, a new study released Tuesday says.

The study, conducted by scientists at Oregon State University, looked at the impact on Northwest snowpack if temperatures warm about 3.5 degrees in the next four decades, as some global-climate models suggest.

"This is a sensitivity study, not a prediction," said Anne Nolin, a professor in the Department of Geosciences at Oregon State University and an author of the study. "We looked at the potential vulnerability to change in winter precipitation."

The study found, for example, that currently 3 percent of winters at Stevens Pass are considered warm — meaning that precipitation that typically falls predominantly as snow instead falls predominantly as rain.

But over the next four decades, the chances of a warm winter at Stevens Pass could rise more than 10 fold, to 37 percent.

Today, 27 percent of Snoqualmie Pass winters are warm; that could more than double, to 57 percent.

Hurricane Ridge in the Olympic Mountains has a 33 percent likelihood of warm winters, but that could jump to 77 percent if global-warming models prove true.

Nolin said she is not saying such a temperature increase will occur.

The study, which will be published in an upcoming issue of the Journal of Hydrometeorology, shows that less than 2 percent of the snow cover in Washington, Oregon, Idaho and Western Montana is at risk from global warming.

But more than half of the at-risk snow is in the Oregon Cascades; about 22 percent of the area in the Oregon Cascades that now gets mostly snow could get mostly rain. The study also found 61 percent of the snow cover in the Olympics, primarily in Olympic National Park, may disappear.

"This region has already experienced the largest declines in snowpack in the Western United States," Nolin said. "What we're able to do now is identify much more precisely where the snow may disappear, based on the warming we expect."

The study showed that about 3,600 square miles of land now covered in winter by low-elevation snow could shift to a climate dominated by rain. Previous studies show that snowmelt in this region already comes nine to 11 days earlier than it did 50 years ago.

Nolin said the shift also could affect community water supplies.

When it rains, water tends to run off immediately, she said. But snow is banked, melting in the spring and early summer and feeding ground-water supplies that store water and keep rivers and streams flowing.

"Snowpack is one of the things that's critically important for recharging groundwater, since it melts slowly and infiltrates, rather than running off as rainfall does," Nolin said.

Susan Gilmore: 206-464-2054 or sgilmore@seattletimes.com