Snowpacks may shrink in half by 2050

<I>Don Cresswell/East Oregonian</I><BR>Mike Burton, with the Natural Resources Conservation Service in La Grande and John Schreier, with the Bureau of Reclamation in Pendleton, take a snow and water measurement east of Meacham on Feb. 28.

Editor's note:

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Do the math. Snowmelt makes up 75 percent of all water in streams throughout the West. Global warming is expected to reduce snowpacks in the Northwest by 40 to 60 percent in the next 50 years.

The challenge is clear, and formidable.

"Population and economic growth already are placing severe pressure on water resources in the West," said Bill Pennell, longtime director of the Atmospheric Science and Global Change Division at Pacific Northwest National Laboratory in Richland, Wash. "Climate change is one more very important factor that has to be taken into account when thinking about the future."

Without significant conservation and increased storage, the future will mean getting by with less water.

"The snowpack is really critical for our water supply," said Caty Clifton, a Forest Service hydrologist with the Umatilla National Forest. "The snowpack is our reservoir for the year."

A significant reduction in that natural reservoir will set off a domino sequence of negative impacts, said Kate Ely, Umatilla Basin hydrologist for the Confederated Tribes of the Umatilla Indian Reservation.

"A reduction in snowpack in the winter will translate into an earlier-than-normal snow melt in the spring," she said. This will result in "less groundwater being stored in the basalt aquifers of the Umatilla Basin and a lower-than-normal summer-time base flow in the Umatilla River.

"With less water recharging the basalt aquifers in the Blue Mountains there will be less groundwater to drive the flow system to the lower Umatilla Basin, where most of the basalt pumping for irrigation occurs," she explained.

Others affectedIrrigators won't be the only group struggling to meet water needs. Smaller snowpacks also translate into less water for hydropower and industry, recreation and sustaining fish habitat.

"This scenario exacerbates an already over-taxed water supply where many farmers cannot satisfy their water rights, groundwater in storage is being mined, and instream flows are minimal at best to meet quantity and quality conditions for fish," Ely said.

Lower river flows mean higher stream temperatures in the summer, when the Umatilla River and its tributaries already are "stressed with water quality limitations," she added.

However, climate change doesn't necessarily translate into less water. Warmer temperatures likely will mean more precipitation in the winter and early spring - mostly in the form of rain rather than snow.

"We've recently examined 20 of the newest scenarios from global climate models. These are simulations performed at research centers around the world," said Philip Mote of the Climate Impacts Group at the University of Washington. For the Pacific Northwest, and specifically the Columbia Basin, those models "mostly project modest - about 5 percent - increases in winter precipitation and bigger decreases in summer precipitation, say in the range of 20 percent."

A 20-percent decrease in summer rain may not be that big a deal for dryland farming regions like eastern Umatilla County. June precipitation at the Agricultural Research Station a few miles east of Pendleton averages 1.08 inches, so a 20-percent dip would mean a loss of just 0.22 inches.

But that could be critical to a dryland wheat farmer banking on a couple of timely rain storms to push his crop from marginal to average or above.

The key problemMore importantly, wetter winters and drier summers highlight a shift to more precipitation when it's not needed, and less when it is - all because of rising temperatures.

L. Ruby Leung, a staff scientist with the Climate Physics Group of the Atmospheric Sciences and Global Change Division of Pacific Northwest National Laboratory, said regional climate change models perfected over the past 10 years point to an average temperature increase of 6 to 7 degrees Fahrenheit by 2050.

The West could be the hardest hit region In the United States, Leung said, because "it's naturally more arid and relies more heavily on snowpack." The Midwest, by contrast, isn't expected to see as sharp an increase in temperature.

"That will have a big impact on the West Coast's major rivers," Leung said of rising temperatures in the West, particularly the Columbia River, and the Sacramento in California.

"As it warms, the amount of mountain area that can hold snow will decrease," said Pennell, a colleague of Leung's until he left the Pacific Northwest National Laboratory last summer to direct NARSTO, North American Research for Tropospheric Ozone. "And there's a high probability of more incidences of warm rain on the snow."

The subsequent reduction expected in the region's snowpack of 50 percent or more by mid century is shocking, but certainly not unprecedented.

"The snowpack has gone down 30 to 50 percent in the Northwest in the last 100 years," Leung said.

Runoff is always an issueScientists also have been recording consistently earlier annual spring runoff in many watersheds. A researcher with the U.S. Geological Survey recently reported that runoff in streams throughout California's Sierra Nevada now comes as much as three weeks earlier than it did in the late 1940s. The Journal of Climate is expected to report soon similar shifts for watersheds in the Northwest.

That trend will contribute to "a larger peak runoff in the winter time, when we don't need it, which could cause flooding problems," Leung said.

In the journal "The Effects of Climate Change on Water Resources in the West," which both Pennell and Leung contributed to, scientists contend that shift in when runoff and precipitation is most commonly available will increase competition for water in the summer, when it's most critical. In the Columbia River system, that means residents and industries will face even tougher choices between water for summer and fall hydroelectric power and releases for salmon runs, not to mention irrigation.

But one thing is certain, to properly plan for the future it will be necessary to take into account "all these fluctuations in precipitation and runoff," Leung concluded.

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