Less snow and less water. Federal study paints bleak picture of American River’s future

Hotter weather, less snow and more water shortages.

The U.S. Bureau of Reclamation offered a bleak vision of the future of the American River watershed Wednesday, releasing an extensive report on how the basin that’s so vital to the Sacramento region’s water supplies will be affected by climate change in the coming decades.

The bureau, which operates Folsom Lake, said the Sierra Nevada foothills east of Sacramento could eventually see shortfalls of as much as 78,000 acre-feet per year unless stronger conservation and water-storage projects are undertaken. Closer to Sacramento, the area’s water agencies will likely have to increase groundwater pumping by as much as 155,000 acre-feet per year, “which would affect groundwater sustainability.” An acre-foot is 326,000 gallons, enough water to serve as many as three households for a year.

Areas served by the American River had a fairly wet winter this year — at least when compared to most of the rest of the state as the California drought continues for a third year. But with each passing year, conditions on the American will likely worsen.

The heart of the problem is the warming climate. Average summer temperatures in the watershed are expected to increase by 7.2 degrees Fahrenheit by the end of the century, the study said. Winter temperatures will climb 4.9 degrees.

Not only does hotter weather increase the demand for water, snowfall will give way to rain — as it has already — making it much harder to operate Folsom Lake and manage the river system for both droughts and flood control. An ample Sierra snowpack acts as backup reservoir space. But if the region receives mostly rain and little snow, the precipitation will overwhelm the system, raising flood dangers while making it harder to store water.

“Climate pressures will make it harder to simultaneously store water for droughts, manage flood risk and protect freshwater ecosystems,” the study said.

The bureau’s study advocates several strategies for coping with climate impacts, including a $300 million “water bank” that’s already being developed in the Sacramento area. The project will install dozens of aquifer storage mechanisms that will take high flows during heavy rainstorms and plant some of the water underground.

In addition, the bureau recommended that regional leaders study the creation of a small reservoir at Alder Creek, off the South Fork of the American River about halfway between Sacramento and South Lake Tahoe. The reservoir would hold 175,000 acre-feet of water — less than one-fifth of what Folsom can hold.

“We must replace the snowpack with storage,” said Andy Fecko, general manager of the Placer County Water Agency, which worked with Reclamation on the study.

Any new above-ground reservoir, even a small one, would likely be expensive and would face numerous legal challenges from environmental groups and others. California hasn’t built a major reservoir since Southern California’s Diamond Valley Lake opened nearly 20 years ago. The study noted that Reclamation is working with El Dorado County officials to begin a feasibility study of the reservoir proposal.