Another dry winter may be ahead in Sonoma and Mendocino counties

It’s too early to say if Sonoma County and surrounding areas will get enough rain this winter to revive the parched landscape and replenish dwindling water supplies, but it doesn’t look good.

“The tilt is toward a drier than normal winter,” said Brian Garcia of the National Weather Service. But, he added, “It doesn’t mean it’s going to be a bone-dry winter.”

Garcia joined forecasters with the Weather Service’s Climate Prediction Center in briefing local water managers and stakeholders Friday.

The message: Don’t expect the kind of above-normal rainfall that would be typical of an El Niño weather pattern.

The opposite is more likely: below normal rainfall common to La Niña conditions that generally produce drier than usual conditions in southern California and the southwest United States and wetter ones in the Pacific Northwest.

The problem, said Scott Handel, lead meteorologist with the Climate Prediction Center, is that Sonoma County and neighboring Mendocino County, where Lake Mendocino is located, lie in a transition zone that adds greater uncertainty to long-range forecasting based on temperature patterns in the Pacific Ocean.

Other atmospheric and oceanographic dynamics that would be better predictors just won’t be evident for some time, Handel said.

In the meantime, the potential for a La Niña “is not great news for us, to be honest,” Sonoma County Emergency Management Director Chris Godley said.

Policymakers need to know “we cannot wish this drought away — that clearly the signals, at this point, don’t lend itself to saying, ‘Oh, it’s just going to be a regular winter,’ ” Godley said.

Their comments came during a virtual meeting hosted by the Sonoma County Water Agency and the Climate Prediction Center to try to get a handle on what lies ahead for the region after two years of critically low rainfall.

Among the chief concerns are conditions in Lake Mendocino, the smaller of the region’s two public reservoirs, which Thursday fell below 20,000 acre feet of storage for just the second time in its history.

Sonoma Water has cut its own withdrawals from the Russian River by nearly 24% this summer and, with state permission, has reduced river flows throughout the watershed to try to preserve as much water in the reservoirs as possible.

In addition, the State Water Resources Control Board issued orders earlier this month curtailing hundreds of water right holders from diverting water from the river, mostly in the upper watershed, so that additional cutbacks in water releases from the lakes could be possible while still maintaining minimum stream flows.

The hope was to keep storage in Lake Mendocino above 20,000 acre feet until at least Oct. 1 so there would be some limited supply in case of another dry winter ahead.

But continued losses from the upper river diminished reserves in the reservoir much more rapidly than was hoped, allowing storage to drop below the target level and raising fears the lake could run dry if winter doesn’t bring enough rain.

“Unfortunately, we couldn’t get people to do what we wanted them to do,” Sonoma Water General Manager Grant Davis said.

Davis said he was more optimistic about Lake Sonoma, which is substantially larger than the smaller reservoir to the north.

Though the lake on Dry Creek now holds more than 116,000 acre feet of water, it’s on course to hit the 100,000-acre-foot trigger that would require diversions to be reduced by a mandatory 30% come New Year’s, Davis said. That still leaves about two years worth of storage.

An acre foot is almost 326,000 gallons of water, or enough to flood most of a football field one-foot deep. Though water usage varies from community to community, in part based on climate and housing density, an acre foot is about what’s needed to supply almost 3½ water-efficient California households for a year, according to the Water Education Foundation.

Davis said missing the Lake Mendocino target by more than a month leaves only enough water for human health and consumption among those who depend on the upper river.

And although officials with the U.S. Army Corps of Engineers, which operates and maintains the reservoir, believe water can be released well into the remaining storage pool without jeopardizing water quality, Davis said he is less confident.

“I’m concerned now, but the lower you go, the more the anxiety goes up,” he said.

Stream flows in the upper river did stabilize somewhat recently, allowing the water agency to gradually slow releases from Lake Mendocino, but improvements are not entirely consistent.

Losses between Ukiah and Healdsburg during July and the first three weeks of August were slightly below those of the same period a year earlier. However more water was drawn from the system between Cloverdale and Jimtown and in the Healdsburg area than in 2020, despite orders from the state.

Davis said it was possible inspections of curtailed water users that began two weeks ago by the enforcement arm of the State Water Board might have accounted for some of the reduced withdrawals.

“Just the fact that they’re down in the Russian River watershed and meeting with large permit holders and showing a presence is, I think, making a bit of difference,” he said. “It’s indicating that they are going to follow through on diversions and see that folks are in compliance.”

State Water Board Enforcement Chief Jule Rizzardo said Thursday that her team had not found any unlawful withdrawals after conducting 14 inspections of the largest diverters, which account for about 30% of the overall potential diversion volume.

But she said only 61% of the curtailed water right holders had complied with the technical requirement of the order. That part requires them to confirm that they have ceased diverting, turned to an alternate water source or claimed an exemption for basic human health and safety needs equal to 55 gallons per person per day.

The best way to earn an inspection is to fail to fill out the simple form, she said, thought “they still may get a visit even though they have responded.”

She added, “We have a lot of tools in the tool box when it comes to compliance assurance,” including aerial imagery and complaints from the public. “The inspections are very important, but they are just one of the tools that we use.”

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.