Study documents shrinking Alaska snow season

Winter comes later, spring sooner along the North Slope of AK

A January 2011 image from the NASA Earth Observatory library shows Alaska completely covered with snow.

Staff Report

The snow season is getting shorter in one of the coldest parts of the U.S. On Alaska’s North Slope, snow is piling up later in the fall and melts earlier in the spring, climate change that is having consequences for communities and ecosystems.

“The timing of snowmelt and length of the snow-free season significantly impacts weather, the permafrost, and wildlife — in short, the Arctic terrestrial system as a whole,” said Christopher Cox, a scientist with CIRES at the University of Colorado Boulder and NOAA’s Physical Sciences Division in Boulder, Colorado.

Cox is co-author of a new study published in the Bulletin of the American Meteorological Society that tracked the changes. Among other things, they found some birds are laying their eggs much sooner, and iced-over rivers are flowing earlier. The study focused on the transition seasons, fall and spring. Since 1975, the snow-free seasoned has lengthened by about one week per decade. From 1975 to 2016, the spring snowmelt has arrived nearly three days earlier every decade, and from 1979-2016, snow onset has arrived later, by about 4.5 days every decade.

The study identified a clear warming trend superimposed on natural year-to-year variations. Eight of the 10 earliest melt dates have occurred since 1990, pointing to the influence of warming Arctic temperatures. 2016 experienced the earliest melt, the latest onset of snow in autumn, and the longest snow-free season in 115 years of record-keeping — about 45 percent longer than the average over the previous four decades.

An evaluation of the data showed different factors driving changes in the two seasons. In the spring, changes in flow patterns of warm Pacific Ocean air from the south were driving earlier spring snowmelt. In the autumn, decreasing summer sea ice has the greatest influence on the timing of the seasonal snowpack.

Specifically, the amount of open water in the Beaufort and eastern Chukchi Seas appeared to be very influential in affecting the temperature along the north coast and the subsequent timing of the onset of snowpack. The extent of open water in the region during autumn has increased significantly in the past several decades, a signal other studies have linked to Arctic amplification.

The rapid expansion of the North Slope’s snow-free season has had consequences for water resources, wildlife behavior, the plant growing season and more, the research team reported in the new paper. For example, on Cooper Island, where a colony of black guillemots has been monitored since 1975, researchers found that the timing of the seabirds’ egg laying correlates with snowmelt, so earlier melt means earlier egg laying. The timing of snowmelt also influenced the timing of peak discharge from the North Slope river system and the start of the vegetative growing season, according to the researchers.

“It’s remarkable how rapidly things are changing in the Arctic and how the longer snow-free season affects so many other patterns–the guillemots, vegetation growth, and fluxes of gases from the tundra,” said Diane Stanitski, co-author of the paper and a scientist at the NOAA Earth System Research Laboratory in Boulder, Colorado.

Long-term datasets from the region help scientists understand the reasons behind long-term changes and predict what the region will face in the future.

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