water reservoir snowpack storage

By Kevin Hecteman

Reprinted with Permission from the California Farm Bureau Federation 

A wet December has left its mark in the mountains, and many of the state’s reservoirs remain at or above average storage levels as 2020 begins.

The state Department of Water Resources took its first snow survey of the year at Phillips Station in El Dorado County last week, and found 33.5 inches of snow and a snow-water equivalent of 11 inches, about 97% of average for the location. Statewide, DWR found a snow-water equivalent of 9.3 inches, or 90% of average.

Although that’s a good start, the next two months will tell the tale, said Chris Scheuring, California Farm Bureau Federation senior counsel.

“We had a decent enough start with a couple of storms, but the last couple of weeks have gone dry again,” Scheuring said. “Everything is going to depend on what happens, really, in January and February, which are statistically speaking the
big months.”

California usually sees about three-quarters of its annual precipitation in December, January and February, according to DWR, with atmospheric rivers being the main source.

The current water year so far is similar to the previous one, with a dry start followed by a cold, wet December that had the state sitting at 74% of average precipitation at the start of January. The U.S. Drought Monitor shows only the far northeastern corner of California—mainly Siskiyou and Modoc counties—as being abnormally dry.

Chris Orrock, a DWR public information officer, said last month ranked as “probably one of the best Decembers on record since 2010,” and said he’s cautiously optimistic about the rest of the season.

“Wish we had a crystal ball, but we don’t,” Orrock said. “We just have to wait to see what the rest of the season brings us.”

Scheuring said that barring a soaking-wet February, irrigation-delivery forecasting and planning can’t really be done before March.

Long-range projections from the National Oceanic and Atmospheric Administration Climate Prediction Center show a 50% to 60% chance of higher-than-average temperatures for almost the entire state, and a 40% to 60% chance of below-average precipitation for its southern half.

Although that combination would lead to a drier-than-normal year, “one or two atmospheric rivers could change that whole scenario,” Orrock said. One hazard of such storms, though, could be found on hillsides scorched by wildfires.

“If you are in an area that was affected by wildfires and we do get these atmospheric rivers, be ready for flooding that you might not normally have seen in the past,” Orrock said.

Fire damage can boost flooding susceptibility for two to five years, he noted.

Scheuring said reservoirs hold good carryover storage from last year, with many reservoirs running near or above their historical average for the year as of Jan. 3, according to DWR.

The main reservoirs for the federal Central Valley Project and State Water Project, Shasta and Oroville, stood at 117% and 95% of average, respectively. The jointly operated San Luis Reservoir was at 93% of average storage.

Millerton Lake behind Friant Dam on the San Joaquin River stood at 100%, while New Melones on the Stanislaus River was at 143% of average and Don Pedro on the Tuolumne River at 121%. Lake Cachuma in Santa Barbara County, famously left out of the state’s drought-busting precipitation bounty in 2017, stood at 72% of capacity and 94% of average.

Even so, Scheuring said, work remains.

“We continue to believe that additional storage is a policy imperative in California,” he said. “All of this uncertainty about precipitation and the chronic year-to-year variability in California’s precipitation patterns just underscores the continuing need for additional storage.”

That storage, he noted, should be designed with rainfall and runoff rather than snowmelt in mind. Projected warmer temperatures mean “what precipitation does come onshore is going to be rain at higher elevations and less snow,” Scheuring said. “That’s not necessarily a good thing, because rain runs off. Snow is impounded by its frozen nature until later in the season.”

In the meantime, “here’s hoping for three or four real good moisture-laden storms that are relatively cold in nature,” he said. “That’s really what
we need.”

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