Lack of spring snowpack bodes ill for many

A dearth of snow on the ground can do more than just bum out skiers and snowmobilers. In areas that depend on snowmelt for fresh water, insufficient snowpack can lead to dry soil conditions, decreased crop production, and widespread wildfires.

White depicts regions covered by snow this year between March 5 and 12. The red and yellow lines, respectively, represent average snow lines for March and February over the past 34 years. Gray areas were blocked by clouds during satellite passes. NASA/Goddard Space Flight Center

If newly released satellite data are any indication, large portions of the already dry northern and western United States are in for another tough year.

Images taken by a NASA satellite launched in December confirmed last week that the northern United States had much less snow cover than average this spring, which followed North America’s warmest winter on record.

Although portions of the Rocky Mountains were still topped with snow during early March, only scattered areas from the Pacific Northwest to New York were covered with the white stuff. The images from space show large snowfree areas extending well into the Canadian provinces of Saskatchewan and Manitoba.

Dorothy K. Hall, a senior research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., presented the findings July 26 at the International Geoscience and Remote Sensing Symposium in the perennially snowless Honolulu.

The smaller March snowpack could be aggravating drought conditions from the Midwest to the Rocky Mountains, Hall says. After all, she adds, up to 75 percent of the yearly supply of surface water in the western United States comes from snowmelt.

Satellite data collected since the mid-1960s show that this spring’s snow cover across North America was among the lowest in the past 30 years, says Alan N. Basist, a research meteorologist at the National Climatic Data Center in Asheville, N.C.

The lower-than-average snow cover continues a trend that stretches back to the late 1980s, says David A. Robinson, a climatologist at Rutgers University in Piscataway, N.J. This extended snow drought follows a period from the late 1960s to the mid-1980s during which North America’s spring snow cover was more extensive than average, Robinson notes.

Scientists don’t know whether the recent trend toward less snow cover in spring is due to a decrease in the overall amount of accumulation or to an increased patchiness in the snow’s distribution.

“It’s probably yes on both counts,” says Robinson. He explains that bare patches of ground, which typically absorb from 80 to 90 percent of the solar radiation that hits them, can create pockets of heat that accelerate the loss of snow over larger areas.

Robinson says other factors, such as long-term changes in the springtime weather patterns that carry warm air northward, also could be causing the snowpack to succumb prematurely.

It’s too early to tell whether the recent trend of early snowmelt results from global warming or natural variability in climate. Says Robinson: “That’s where I wish we had a thousand years of climate records, instead of just a couple of decades of satellite data and a century or so of weather station measurements.”

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