Recent snowstorms may bolster California hydroelectric output this summer

All the rain that has led to swollen rivers and flooding in parts of San Diego and large portions of Southern California has coincided with multiple snowstorms that blew across the Sierra Nevada Mountains in the northern half of the state.

That may translate to a second consecutive year of robust output from the state’s hydroelectric power plants, which would help bolster the electric grid this summer. But officials at the California Independent System Operator, which manages the power system for about 80 percent of the state, aren’t celebrating yet.

“It’s always encouraging to have a wet winter and a good snowpack,” California ISO spokeswoman Anne Gonzales said, “but it’s too early to tell the full impact of the recent rains and snowfall on electricity supplies through the summer and into fall.”

After a very slow start, rain and snowfall totals are growing in the wake of a series of atmospheric rivers — columns of condensed water vapor that produce significant amounts of precipitation.

The UC Berkeley Central Sierra Snow Lab, located at nearly 7,000 feet elevation at the Donner Pass in the Sierra, recorded more than 5 feet of snow from a series of storms in the past week.

What’s called “snow water equivalent” is a critical metric that refers to the overall amount of water the snowpack contains and then releases when it evaporates. Five weeks ago, the statewide snow water equivalent stood at just 28 percent; as of Thursday morning it had grown to 75 percent.

“We’re a little behind, but overall the winter’s been pretty normal,” said Andrew Schwartz, the Snow Lab’s lead scientist. “At the lab, we’ve had just over 5 feet of snow in the last eight days, so it’s definitely helpful.”

Healthy amounts of snow and rain fill reservoirs that feed the state’s large hydroelectric plants. The power generated by those facilities add much-needed megawatts of electricity to the state’s grid.

In wet years, hydroelectricity can account for roughly 20 percent of California’s energy mix. But in dry years, it can drop to around 6 percent. That means grid operators have to rely more heavily on other energy sources such as natural gas or out-of-state imports, especially during the hottest months of summer when electricity demand soars.

After multiple years of drought, last year was one big, wet blockbuster. The Snow Lab measured 754 inches of snowfall in the winter of 2022-23, making it the snowiest winter since 1951-52.

California ISO officials said hydro production in July 2023 was 56 percent higher than July 2022.

But energy analysts say a healthy snow pack in 2024 won’t deliver the same punch as last year. That’s because water levels at the big hydro facilities in the northern part of the state remain close to capacity after last year’s precipitation.

“The storage facilities are healthier going into this spring than they were last spring,” said Jeff Richter, principal owner of Energy GPS, an Oregon-based energy analytics company. “So we’re not able to fill the tank as much.”

Lake Shasta near Redding feeds the Shasta Powerplant, which produces hydroelectricity for the 15-state western power grid. As of late Wednesday evening, Lake Shasta was 125 percent of average and 83 percent capacity, according to the Department of Water Resources.

Reservoir levels at the Oroville Dam in the Sierra Nevada foothills, which serves the Edward Hyatt Power Plant, stood at 130 percent of average and at 77 percent capacity.

Richter said there’s no doubt that “back-to-back good water years is a good thing,” but an extremely hot summer across California and most of the West could still spell trouble for the electric grid.

“The caution is if we get hot on the coastal part of the state, our load — our power demand — will tighten the system, regardless how much hydro we have,” Richter said.

That’s one of the reasons the California ISO is taking a wait-and-see attitude.

The grid operator won’t come out with its annual summer assessment until May, after crunching data compiled by the California Department of Water Resources. Only then will California ISO officials determine the expected hydro conditions.

Mother Nature plays a big role looking ahead.

If temperatures rise sharply and melt the snow in the Sierra too quickly, state water officials may be forced to divert water for flood control instead of using it for electricity.

The Department of Water Resources also discharges water for other reasons, such as agriculture and fish habitat. Depending on conditions, California ISO managers say hydro generation changes frequently — sometimes, even from one hour to the next.

For now, the recent snowstorms are certainly good for the ski resort business.

Palisades Tahoe, formerly known as Squaw Valley, said as of Wednesday morning, it had received 53 inches of snow since the start of February.

All the snowfall “has transformed the mountain top to bottom,” the resort said on its X, or Twitter, feed.