CORVALLIS, Ore. - Global warming in coming decades may cause the disappearance of large areas of the low-elevation snowpack in the Cascade Range of the Pacific Northwest, a new study concludes, with significant impacts on area ski resorts that will face warm winters far more often than they do now.

Similar impacts are also possible for portions of the southern Cascade Range in Washington and large parts of the Olympic Range in that state, researchers said. The report, by geographers from Oregon State University, has been accepted for publication in a future issue of the Journal of Hydrometeorology, a publication of the American Meteorological Society. The work was funded in part by the U.S. Geological Survey and NASA.

The study indicates that less than 2 percent of the current snow-covered area is modeled to be at risk in the future in a four-state Pacific Northwest region that includes Idaho and parts of western Montana. But more than half of all the "at risk" snow is in the Oregon Cascades, and about 22 percent of the area in the Oregon Cascades could soon experience precipitation that falls as rain in the winter, rather than as snow. In another area that could be strongly affected by global warming, 61 percent of the snow cover in the Olympic Range, most of which is in Olympic National Park, may disappear.

The potential for changes in snow and rain precipitation patterns, experts say, could ultimately affect not just ski resorts but also stream flows, fisheries, flood control, hydroelectric power generation, irrigated agriculture and many other water-related issues.

"Previous studies show that snowpack has fluctuated widely in the past, but appears to be trending downward in the Pacific Northwest since the 1920s," said Anne Nolin, an assistant professor in the OSU Department of Geosciences. "This region has already experienced the largest declines in snowpack in the western United States. What we're able to do now is identify much more precisely where the snow may disappear, based on the warming we expect. We've never before had projections that are this specific in their spatial scale."

For their study, Nolin and Chris Daly, an associate professor of geosciences, used widely accepted global climate models which, on average, suggest this region may warm about 3.5 degrees Fahrenheit in the next 40 years.

Global climate models make relatively simplistic simulations of the climate and vary in their predictions, Daly said, and the warming projections will undoubtedly change as the models are refined and made more sophisticated.

"This research was designed as a sensitivity study that considers a range of projected future conditions," Daly said. "While those projections may be uncertain, it is clear that the snowpack in the Cascades and Olympics is highly temperature-sensitive, meaning that even slight increases in temperature could have serious implications for Pacific Northwest snow and water issues."

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

Some of the most profound impacts may be on ski resorts in the region, the scientists said, especially those at the lower elevations.

For instance, based on the increase in temperature that is expected 40 years from now, the study showed that Mt. Hood Meadows, a popular ski area near Portland, Ore., may experience warm winters about seven times more frequently than it does now - going from a warm winter 7 percent of the time to 47 percent of the time. A "warm winter" means that, based on the elevation of the ski area, climate conditions and other localized geographical conditions, precipitation that now falls predominately as snow during December, January and February will instead fall predominately as rain.

Another ski area in the central Cascade Range, Willamette Pass, may go from warm winters 3 percent of the time to 67 percent of the time - 22 times as often. Following are data for a range of other ski resorts in Oregon and Washington:

Ski Resort Frequency of warm winters now Frequency of warm winters in the future

Timberline: 7 percent 43 percent

Mt. Hood Ski Bowl: 30 percent 73 percent

Cooper Spur: 40 percent 73 percent

Hoodoo: 7 percent 67 percent

Mt. Bachelor: 0 percent 33 percent

Warner Canyon: 20 percent 63 percent

Mt. Ashland: 7 percent 40 percent

Spout Springs: 0 percent 40 percent

Mount Spokane: 27 percent 57 percent

Bluewood: 3 percent 53 percent

Mt. Baker: 3 percent 33 percent

Mission Ridge: 7 percent 37 percent

Crystal Mountai:n 0 percent 47 percent

White Pass: 0 percent 47 percent

Summit/Snoqualmie: 27 percent 57 percent

Stevens Pass: 3 percent 37 percent

Hurricane Ridge: 33 percent 77 percent

While having some of the most direct impacts on ski operations, the researchers said, the potential effects of global warming and associated snowpacks would not be confined to them. Studies have already shown that plants are leafing out earlier, growing seasons are expanding, and spring is coming sooner, Nolin said.

"Current global climate model predictions suggest we're going to see more frequent winter rain events and the snow melt in the spring will begin earlier, which would affect planning for irrigation and flood control," Nolin said. "And 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."

Certain rivers that depend more on springs and groundwater than others, such as the McKenzie River or Deschutes River, would probably face more hydrological and biological impacts that those that are driven primarily by rain, Nolin said.

Reductions in summer stream flow as a result of diminished snowpack would be a special problem for fisheries management, the researchers said.

Similar concerns would almost certainly be at work in the Sierra Nevada range of California, the researchers said, but an analysis of that region was not a part of this study.

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Anne Nolin, 541-737-8051