Snow melt declining in western U.S.

From the Rockies all the way to the Cascades, springtime snowpack and snow melt has declined by about 10 percent over the past 50 years in the western U.S. That’s according to Philip Mote, director of the Oregon Climate Change Research Institute at Oregon State University. Dr. Mote is an expert on snowpack – snow that accumulates in forests, valleys, and mountains – in the western United States. He told EarthSky:

It’s a combination of less accumulation and more melt. The snow is melting earlier in the spring. So when you get to the late summer when most of the snow has melted and it’s not raining yet, the stream flow can be quite low in some places.

Much of the agriculture in the western U.S. is grown in fairly arid climates and the irrigation water, in large part, comes from snow melt. So we have to watch very closely what’s happening with snow.

Less snowmelt meas less available water for irrigation. Dr. Mote said that this snowpack melt is a consequence of our warming climate. He added that, since climate warming is expected to continue, water managers in the western U.S. are figuring out ways to depend less on water from snow.

It’s not so much new sources as smarter use of water, covering or lining canals to reduce leakage or evaporation, using drip irrigation instead of sprinklers, moving away from large green lawns in areas where water supply is a problem.

In the Pacific Northwest, the situation is most apparent. Springtime snowpack has decreased by as much as 25%, said Mote.

The swath of largest impact of warming on western snowpack extends from the Sierra Nevada mountains of California up through Oregon, Washington, and into southern British Columbia. These are locations where there’s fairly wet winter climate, fairly frequent snowstorms, but the temperatures are fairly mild, so a little bit of warming can really change the amount of snow on the ground in the spring.

He explained that, historically, the date for measuring snowpack has been April 1st of any given year. That’s the date on which – again, historically – the most snowpack has accumulated, with little having melted. Dr. Mote talked about the visible decline in snowpack outside his hometown of Corvallis, Oregon.

There’s a peak about 4100 feet – Mary’s Peak – one of the hills in the coast range of Oregon, and the only location in Oregon where U.S. government snowpack measurements go back. It used to be fairly common for the April 1st survey on Mary’s Peak to have quite a bit of snow. By the 1980’s it was getting common to have no snow on April 1st.

Now it’s quite rare to have no snow on the 1st. Philip Mote explained how colleagues in California, led by climatologist David Pierce of the Scripps Institution of Oceanography, were able to determine, using climate models, that the snowpack melt his own team had observed in the western United States was due to the warming temperature caused by our own greenhouse gas emissions. Snowpack melt is expected to accelerate, he added.

March 24, 2011

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