#Snowpack news: “It is a bigger decline than we had expected,” — Philip Mote

Westwide SNOTEL basin-filled map March 4, 2018 via the NRCS.

From Discover Magazine (Tom Yulsman):

Thanks in large measure to warming temperatures, the average snowpack in U.S. western states has dropped by 15 to 30 percent since 1915.

The water in that lost snowpack is comparable in volume to Lake Mead. With a maximum capacity of 9.3 trillion gallons, Mead is the West’s largest manmade reservoir.

The new data on snowpack declines are among the striking results of a study led by Philip Mote, director of the Oregon Climate Change Research Institute at Oregon State University. As part of the study, Mote and his colleagues analyzed measurements from 1,766 snow-monitoring sites in the western United States going back more than a century. The researchers found that greater than 90 percent of those sites experienced declines in snowpack. Of those, 30 percent were found to be statistically significant.

“Declining trends are observed across all months, states, and climates, but are largest in spring, in the Pacific states, and in locations with mild winter climate,” Mote and his colleagues write in their paper, published on March 2 in the journal NPJ Climate and Atmospheric Science, a Nature publication.

“It is a bigger decline than we had expected,” Mote says, quoted in a release. The primary cause isn’t less snowfall, but warmer temperatures. “In many lower-elevation sites, what used to fall as snow is now rain,” Mote notes.

The West’s snowpack comprises nature’s own water storage reservoir — and a gargantuan one at that. “Mountain snowpack stores a significant quantity of water in the western U.S., accumulating during the wet season and melting during the dry summers and supplying much of the water used for irrigated agriculture, and municipal and industrial uses,” Mote and his colleagues write in their study.

Warmer temperatures bring spring-like weather earlier than in the past. As this trend continues, increasing spring rain and earlier runoff means declining water supplies running downstream from nature’s snowpack reservoir in summer and fall — just when farmers and cities have very significant water needs.

From Oregon Public Broadcasting (Courtney Flatt):

Researchers said the decline in snowpack is connected to warming temperatures. That could have a big effect on wildlife, agriculture, cities and towns. They depend on snowmelt to supply water during the dry summer and fall months…

The study found 90 percent of long-term snow monitoring sites in the West have less snow than 100 years ago. More than 30 of those sites saw significant decreases that could not have happened by chance, statistically, Mote said.

Researchers used a model that computed the amount of snow on the ground every day — using actual weather readings. They took the weather readings from 1,766 sites across the West. They ran the model over a time period of 100 years with real weather data.

They mostly keyed in on one date: April 1, historically a high-point for snowpack.

They found the biggest changes in snowpack in the spring in California, Oregon and Washington, and in places that had milder winters.

Then, they “re-ran the model without the warming trends that have been observed, and lo-and-behold, the large number of [declining snowpack] trends went away. It ended up being more balanced, 50-50,” Mote said.

They took that as another clear sign that snowpack is decreasing because of warmer temperatures, not a lack of precipitation.

One of place that’s seen the most snowpack decreases in the West is Eastern Oregon. Mote said the most recent low snow year in 2015 was a benchmark of where water problems have happened — and will continue to happen.

“The solution isn’t in infrastructure. New reservoirs could not be built fast enough to offset the loss of snow storage — and we don’t have a lot of capacity left for that kind of storage. It comes down to managing what we have in the best possible ways,” he said.

The study was published in NPJ Climate and Atmospheric Science, a Nature publication, and was funded by the National Oceanic and Atmospheric Administration’s Regional Integrated Sciences and Assessment (RISA) program, and the U.S. Environmental Protection Agency’s Office of Atmospheric Programs.

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