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Study: Alaska's future looks more rainy, less snowy

Yereth Rosen

Alaskans of the future might have to stock up on ice cleats and endure disappointing snow seasons. A newly published study calculates the degrees to which precipitation falling from the sky will be rain instead of snow, a transformation expected over the rest of the 21st century as the far-north climate warms.

The study, published in the June issue of the journal Hydrological Processes, uses a model based on decades of weather data from around the state. It applies the derived calculations of past temperature and precipitation to a suite a suite of well-respected climate-prediction models used by the Scenarios Network for Alaska and Arctic Planning at the University of Alaska Fairbanks.

The result is a range of forecasts for future precipitation mixtures around Alaska, with snowy seasons expected to become more rainy.

“By the end of this century, winter conditions could be pretty different in many places than they are now,” said lead author Stephanie McAfee, formerly of Scenarios Network for Alaska and Arctic Planning and now an assistant professor at the University of Nevada Reno.

The change might mean some lifestyle alterations, McAfee said. “As someone who likes snow, this is sad for me,” she said.

The study focuses on three regions: Western Alaska; Southeast Alaska and the Gulf of Alaska coastal area; and the Arctic. Since the southern parts of Alaska are warmer, incremental temperature increases are more likely to result in more rainfall there than in the colder, more northern areas, McAfee said.

The most dramatic changes are forecast for Western Alaska, which “may be particularly sensitive to snow change in the coming decades,” says the study, co-authored by John Walsh of UAF’s International Arctic Research Center and Scott Rupp, director of UAF’s Scenarios Network for Alaska and Arctic Planning. The region already experiences a significant number of rain-on-snow events, “and warming could tip the balance, shifting the region from snow-dominated winters to more consistently mixed rain and snow,” the study says.

Under the most extreme warming scenario, February in the southern part of Western Alaska will become a rainy month, not a snowy month. Under that scenario, by the end of the century, rain will be falling in that part of the state on at least three-quarters of the days when precipitation occurs.

In the Arctic, the snow-rain mixture will tilt to varying degrees depending on the climate scenario used, to later autumn snow and more late-spring rain, according to the forecast. That could mean changes for how the tundra there is used by people, animals and even plants. The length of the annual snow-free period is important for permafrost stability, vegetation, wildlife and human use of the land for subsistence food gathering and natural resource development, the study points out.

In the Southeast Alaska and Gulf of Alaska coastal area, the big changes will likely be in February and March, according to the study. The area has already been affected by a gradual shift in the rain-snow balance, a change that has harmed yellow cedar by stripping away the snow insulation that protects those trees’ roots from cold air, according to U.S. Forest Service research.

Yet unclear is how the rain-snow mix will turn out in Alaska’s most populous area -- Anchorage and the surrounding Cook Inlet region. The model that McAfee and her colleagues developed on the basis of past weather data did not closely track events in the Cook Inlet region, she said. Complex storm patterns, their interaction with the region’s mountains and the quirks of high-altitude weather, including occasional temperature inversions, make the region more difficult to model, she said.

“The Cook Inlet area was very complicated,” McAfee said. Further work will be needed to come up with any calculations for precipitation-mix forecasts in the Cook Inlet region.

Across the circumpolar north, the growing trend toward rain rather than snow has already caused concern, especially about events known as rain-on-snow and their impacts to wildlife.

An extreme rain-on-snow event on Canada’s Banks Island is blamed for a die-off of about 20,000 musk oxen in 2003, for example. In Norway’s Svalbard, scientists found rain-on-snow events caused die-offs of reindeer, ptarmigan and voles, though not arctic foxes, according to a study published in Science magazine in 2012.

Rain-on-snow also increases avalanche risk, a well-known hazard in temperate mountainous areas.

There are other potential, and possibly less obvious, effects of changes to the rain-snow mix that warrant further research, McAfee said. Salmon-spawning habitat, for example, could be affected by the hydrological changes that result from more rain and less snow, she said.  Normally, after a winter’s worth of snow has accumulated, streams swell in the spring, she said. “But if it rains in the winter, that spring flush may not be as big,” she said.