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NW Fishletter #380, April 2, 2018
 Loss Of Snowpack Will Mean Rising Tensions For Columbia Basin Water
Thirty-two kilometers cubed. Or, 26 million acre-feet. That's enough water to fill Lake Mead--the West's largest reservoir, held back by Hoover Dam, and used to irrigate farmland and provide wa-ter to some 20 million people in Arizona, California and Nevada.
It's also the water equivalent of spring snowpack that--on average compared to a century ago--is no longer being stored as snow on mountains and foothills across the Western U.S.
Since 1915, the West's total snowpack on April 1 has dropped by an average of 21 percent, ac-cording to an article published this month in the research journal npj (Nature Partner Jour-nals) Climate and Atmospheric Science.
The article, titled "Dramatic declines in snowpack in the western U.S.," reports that despite higher elevations in the up-per Columbia River that will help shield the basin from immediate impacts of declining snowpack, hydropower will not be immune to the growing demand for dry-season water.
In interviews with NW Fishletter, Philip Mote, an Oregon State University professor and director of the Oregon Climate Change Research Institute, and Dennis Lettenmaier, geology pro-fessor at UCLA, said water users in the Columbia River Basin should prepare for more runoff earlier in the year, and less in the late spring and summer.
The researchers found that in the Pacific Northwest, snowpack loss is likely caused by warmer temperatures, not less precipitation. "If you average it over the long term, precipitation hasn't changed that much. But the temperature has, and warmer temperatures mean less snowpack." Letten-maier said. He added, "The kind of temperature changes we've seen over the period of study is well less than 1 degree Celsius [1.8 degrees Fahrenheit], generally." That means sometimes, especially in lower elevations, what formerly came down as snow now falls as rain.
Impacts to the Columbia River Basin haven't been as severe, so far, because so much of the ba-sin is fed by snow accumulated at higher elevations. "The Columbia River is interesting," Lettenmaier said. "Something like 30 percent of the discharge comes from Canada, and that is mostly at pretty high elevation. It's somewhat less susceptible than the rest of the basin. But when you look farther downstream, there's a real mix."
Both Lettenmaier and Mote pointed to the Yakima River Basin as an example of a basin feeding into the Columbia River with characteristics that, even with small temperature changes, will experi-ence less snow and an earlier runoff.
Mote said snowpack losses are even greater than he anticipated when he and his colleagues set out to update their 2005 study. With the additional data, they found declining snowpack in 92 percent of the snow monitoring sites with long records, and one-third of them--232 of 699 sites--had signifi-cant losses.
Conversely, only 2.2 percent--or 16 sites--had significantly more snowpack, on average. The declines are greatest in the spring. In addition to long-term records and modeling, the study looked at satellite images, available since 1967, which show June has the biggest losses in snowpack.
Overall, the declines are largest in the Pacific states--Washington, Oregon and California. Most of the largest negative trends are in eastern Oregon and northern Nevada, but losses greater than 70 percent were also found to occur in California, Montana, Washington, Idaho and Ari-zona, the study said. And, the study found, locations with the largest snowpack losses tend to have mild, wet climates with mean winter temperatures above 30 degrees and more than 7.8 inches of pre-cipitation each month. But other locations that experienced large losses of snowpack are cooler, drier climates, where mean winter temperatures range from 23 to 32 degrees.
"Snow is an important part of the total hydrological story. It's a piece of the climate puzzle that hadn't really been looked at," Mote said. And in a basin like the Columbia River, where there are so many competing interests for water, the amount of naturally stored water can have big impacts. "When Dennis and I started doing this work 15 years ago, I thought some of the water policies would be farther along [by now]," he said.
Mote added that while the Columbia's vast system of reservoirs can help ameliorate the impacts, those reservoirs will become harder to manage because of competing interests. "You can make it a priority to drive the system for hydropower, or flood control, but in a changing climate the others are harder to manage. Can you manage it to meet all of the BiOp flows?" he asked.
The discussion portion of their article says building more reservoirs is not the an-swer. "The magnitude of these changes relative to the built storage (reservoirs), and the certainty with which continued warming will lead to continued declines at a similar or increasing rate, illustrates the immense challenge facing western water managers," the article says. "Solutions cannot consist solely of future infrastructure: new reservoirs cannot be built fast enough to offset the loss of snow storage, so solutions will have to lie primarily in the linked arenas of water policy (including reservoir operat-ing policies) and demand management."
Lettenmaier said new storage can't be built fast enough, considering the long environmental re-view necessary to create new reservoirs. But also, he said, "There's no place to put them. There are minor exceptions, but the good sites basically got used."
Lettenmaier noted that hydroelectric dams are already operated under the constraints of releas-ing water at certain times to aid in fish migration. "When runoff happens earlier in the year, it will be more difficult to keep enough water for fish later in the year," he said, adding, "That's the ten-sion."
But in addition to hydropower and fish, dam managers will also have to consider water storage for irrigation, municipal and industrial use, and flood control. He noted flooding was one of the pri-mary reasons dams were built on the Columbia River. "Before dams, floods did a lot of damage," he said. "And with warmer temperatures, you've got new issues with flood control."
Lettenmaier believes figuring out reservoir management will become a key question as the West's snowpack continues to diminish.
"All of this works into the discussion of how that reservoir system is operated--how much for flood control, versus water supply storage for irrigation, versus how the hydroelectric system is oper-ated, and a lot of that has to do with when the power gets generated," he said. "It's a very compli-cated situation. The way in which the reservoirs are operated in all likelihood will change as we go forward." -K.C. Me-haffey
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