#Snowpack is melting fast, despite April storms — The High Country News #runoff

Westwide SNOTEL map April 23, 2016 via the NRCS.
Westwide SNOTEL map April 23, 2016 via the NRCS.

From The High Country News (Paige Blankenbuehler):

Throughout late March and into April, much of the West experienced unseasonably warm days. Then, in late April, temperatures plummeted in Southwest Colorado’s San Juan Mountains and more than 2 feet of wet, heavy spring snow fell. Suddenly, ski boots were out again and for a day or two, it felt like winter was back.

But those storms have only helped a small fraction of the West, with much of the moisture buoying snowpack levels along the Eastern Rockies in Colorado and Wyoming. Meanwhile, the rest of the region is on the opposite trajectory, losing snowpack at record-breaking rates.

At the beginning of April, snowpack levels across the region were “near normal,” says Cara McCarthy, deputy director for the National Water and Climate Center in Portland, under the Natural Resource Conservation Service. The season was off to a slow start with sporadic storms in October through December, but January winter precipitation increased levels across all states, according to NRCS SNOTEL sites, which measure snow depth at thousands of stations nationwide. For months, most of the region hung on to above-normal snowpack measurements.

But in just the few short weeks since, that snow is melting faster than climate hydrologists have seen in nearly four decades, bringing the snowpack far below normal in most states in the West…

Temperature has been a major factor in the accelerated melting, although minimal snowfall has also played a role. According to the NRCS and National Oceanic and Atmospheric Administration, much of the Pacific Northwest, California, Idaho and Montana have experienced abnormally high temperatures between the beginning throughout April — in some places departing from historical averages by as much as 10 degrees Fahrenheit. Colorado and parts of New Mexico and Arizona have been more or less normal.

The quickly diminishing snowpack, which acts as a natural water-storage system for Western cities that depend on winter snow for water, portends a more variable future at the whims of a changing climate, says Noah Diffenbaugh, associate professor at Stanford and a research at the Woods Institute for the Environment.

“We find that as warming continues, there’s a robust response of the climate in the West toward more rain and less snow,” Diffenbaugh says…

Water infrastructure has been built around the assumption that a reasonable quantity of water will remain as snow at higher elevations until the temperature warms. As warming occurs earlier in the season and snowpack diminishes faster, it runs into reservoirs prematurely and resource managers may need to release water to make space available to prevent floods…

From a water management perspective, the snowpack readings so far this year are troubling, but they may start to feel normal in coming decades. According to the Intergovernmental Panel for Climate Change, the climate is on track to warm 4 degrees Celsius by the end of the century. If that happens, what we consider “extreme” now — rapid, early spring snowpack melt — “will happen more like 40 to 80 percent of the time,” Diffenbaugh says.

From 9News.com (Matt Renoux):

By early May, Denver Water will start sending water out of the Dillon Reservoir to make room for the spring runoff. The Lower Blue River will go from 100 cubic feet per second potentially up to 1,800 CFS at a time when other rivers and steams will also start flowing much faster as well.

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