Questions about dams posed by West’s shrinking snowpack — The Mountain Town News

Hoover Dam, located near Las Vegas, was completed in 1936 and creates Lake Mead. Photo/Allen Best

From The Mountain Town News (Allen Best):

Engineering marvels of 20th century challenged by warming of the 21st

Lake Mead has become a benchmark for worsening water woes of the West. It was something else in 1936, when completion of Hoover Dam was a happy story of triumph, a display of ingenuity and determination for a nation still mired in the Great Depression. At last, the unpredictable Colorado River was tamed! It’s flood waters were finally harnessed to provide electricity but also water for expanding farms and especially for growing cities, Los Angeles first but in time others, too.

It was a time of dam-building in the West, creating reservoirs large and small. Later on the Colorado River, in Glen Canyon, came another dam, creating a water bucket, Powell, almost as big as Mead. To the north, on the Columbia there was Grand Coulee, and in the foothills of the Sierra Nevada and the Colorado Rockies still other dams and reservoirs, canals, tunnels and pipelines, collectively the hydraulic infrastructure that was the ultimate expression of Manifest Destiny.

The dam-building did not subside until the 1970s when, to the dismay of Westerners by then accustomed to a seemingly inexhaustible federal budget for ever more hydraulic manipulation, President Jimmy Carter’s approved what was commonly call a “hit list” of unjustifiable new dams.

By then, virtually every significant river in the West had been plugged or otherwise tapped in ways that eliminated any naturalness to the flows. But the hum an-built infrastructure was premised on the mountain snowpack itself, the major source of water in the West, melting in a somewhat predictable sequence during spring and summer.

Now this vision is being challenged by warming temperatures and changed hydrology. A new study finds declines at more than 90 percent of snow monitoring sites with long records across the western United States. A third of those declines are significant. The declines, they say, have occurred across all months, states and climates. However, the largest declines have occurred in spring, in the Pacific states, and in places with mild winter climates.

Lake Mead is cited in the report as a reference point. The average April 1 snow-water equivalent since the mid-20th century has declined roughly 15 to 30 percent. Authors of the study say this decline is comparable in the capacity of Lake Mead, the largest man-made reservoir in the West.

“It is a bigger decline than we had expected,” said Philip Mote, lead author of the study and director of the Oregon Climate Change Research Institute at Oregon State University. “In many lower-elevation sites, what used to fall as snow is now rain. Upper elevations have not been affected nearly as much, but most states don’t have that much area at 7,000-plus feet.”

Mote and his colleagues attribute the snowpack decline to warmer temperatures, not a lack of precipitation. But the consequences are still significant. Earlier spring-like weather means less precipitation will linger in the mountain in the form of snow. That, in turn, results in lower volumes of water in rivers and declined reservoir levels during late summer and early fall.

“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,” says Mote in a press release from Oregon State. “It comes down to managing what we have in the best possible ways.”

The study, published last week in NPJ Climate and Atmospheric Science, builds on work that Mote and others reported in 2005 showing that the warming climate was influencing the snowpack and runoff.

Other studies have also painted a picture of a warming climate causing, at least in places, a drying effect. In February 2017, two researchers reported that precipitation in the seven-state Colorado River Basin during 2000-2004 averaged 6.1 percent less than in the 20th century, but flows had declined 19.3 percent.

The study authors, Brad Udall of Colorado State University and Jonathan Overpeck, now of the University of Michigan, pointed to rising temperatures in the 21st century of 1.6 degrees Fahrenheit as a substantial cause of the reduced flows. They predicted further declining water flows in the Colorado River Basin of 35 percent or more during this century.

Udall, a senior climate and water research scientists at CSU’s Colorado Water Institute, says the new study dramatically reinforces what was already broadly understanding.

“I don’t think this fundamentally changes anything. Anybody who has been paying attention already knows this. But it’s always good to get prodded with a sharp stick in the side to make sure you’re not falling asleep,” he said.

Similar to other studies, the new report finds the snowpack in coastal states—California, Oregon and Washington—is most vulnerable to rising temperatures. They receive more precipitation because of the influence of the Pacific Ocean. Also, more of the snow falls at temperatures near freezing. Because the Cascade Mountains, which transect the region, are not as steep as the Rocky Mountains, they have more area that is affected by changes in temperatures.

“When you raise the snow level 300 feet, it covers a much broader swath than it would in the inland states,” Mote said.

Some sites did have increased snowpack. California had the most, but lingering drought during the past decade erased most of the gains. Snowpack declines still dominated. Most other Western states had only one or two sites with increased snowpack.

Mote sees the warming temperatures requiring a fundamental change in water delivery thinking.

“The amount of the water in the snowpack of the Western United States is roughly equivalent to all of the stored water in the largest reservoirs of those states,” he said. “We’ve pretty much spent a century building up those water supplies at the same time the natural supply of snowpack is dwindling.

“On smaller reservoirs, the water supply can be replenished after one bad year. But a reservoir like Lake Mead takes four years of normal flows to fill. It still hasn’t recovered from the drought of the early 2000s.”

Some have even called for the dismantling of some of this water infrastructure, particularly Glen Canyon. The thinking is that both big buckets on the Colorado River will no longer be needed because of the warming, drying climate. Mead can hold 27 million acre-feet of water and Powell 24 million acre-feet, or more than four times the annual flows of the Colorado River. However, the two reservoirs, brimming with water at the turn of the century, have barely been half for the last 15 years.

The new study makes no mention of this argument but does warn that water managers in the West face an “immense challenge” posed by the magnitude of changes caused by continued warming relative to the built storage.

“Patterns of water use that became established (even entrenched) during the climate of the past cannot be changed without intense political effort owing to large cultural, economic, and infrastructure investments in the status quo ante” the report concludes. ‘”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 operating policies) and demand management.”

Udall makes the same point. He sees new reservoirs offering little help. “It’s like opening up a new bank account when your salary goes down and thinking it will help,” he says. “I just don’t know where the new infrastructure can help much when you’re seeing declining snowpack.”

About Allen Best
Allen Best is a Colorado-based journalist. He publishes a subscription-based e-zine called Mountain Town News, portions of which are published on the website of the same name, and also writes for a variety of newspapers and magazines.

West Drought Monitor March 6, 2018.
Westwide SNOTEL March 11, 2018 via the NRCS.