Just because North Bay reservoirs are full, it doesn’t mean the drought is over, experts say

It’s a busy time at the Lake Sonoma Marina, where the phone “has been ringing off the hook” with folks calling about boat rentals and slip leases for what all signs suggest will be a blockbuster year for recreation at local reservoirs.

But “an unusual amount of people” also are coming by just to gaze at the lake and the deep reserve of water accumulated since a series of winter storms reset the course for the region after three years of severe drought, Lake Sonoma Area Resort owner Rick Herbert said.

There is a touch of miracle in the sudden, drastic reversal that has brought Lake Sonoma from the lowest point in its nearly 40-year history on Dec. nine to 99.3% of its water supply threshold in just 10 weeks.

The earthen sides of Lake Sonoma’s basin had been increasingly exposed as the water receded in recent years, revealing trees poking up from the lake bottom in the shallow arms. Now it is full, at level with the marina lawns and the private boat ramp, which had been out of operation for two years, Herbert said.

“We’re all shocked,” said Grant Davis, general manager of Sonoma Water, which manages the water supply pool at lakes Sonoma and Mendocino and supplies water to more than 600,000 consumers in Sonoma and northern Marin counties through its wholesale contractors.

And really, said Herbert, “it all happened in about three weeks,” during the storms that raged Dec. 26 to Jan. 17.

But so far, the last month has been essentially dry, but for a few splashes of rain here and there totaling just over an 1 1/2 inches at the Charles M. Schulz-Sonoma County Airport.

That’s one reason experts aren’t ready to call the drought over, despite full water levels at lakes Sonoma and its smaller, more northerly counterpart, Lake Mendocino.

“You have to go back to what happened last year” after early season rains, Davis said. “The spigot just turned off,” resulting in an exceptionally dry start to the year and a third season of below average rainfall.

While recent winter storms have filled reservoirs, they haven’t had time to restore groundwater or allow for the landscape’s complete recovery, either.

Season-to-date rainfall for Santa Rosa is 25.83 inches, 115% of average for this time of year, National Weather Service meteorologist Roger Goss said. But we’re nearing the end of what typically are the wettest three months of the year — December, January and February — so hopefully, March is wet enough to raise the season’s rainfall up to normal of 33.78 inches between Oct. 1 and Sept. 30, the technical water year.

Already, this season is wetter than both 2019-20, which had 19.35 inches over 12 months, and 2020-21, which had 13.01. Last year, 2021-22, there was 27.13 inches, just above the amount of rain that has fallen this season so far.

But the U.S. Drought Monitor still has Sonoma County and the surrounding region characterized as in “moderate drought,” along with more than half the state of California. About 33% of the state remains in a condition of “severe drought,” according to the latest U.S. Drought Monitor release on Thursday, while 15% has improved to “abnormally dry.”

The Sonoma County Board of Supervisors is expected in April to reconsider whether to extend its emergency drought proclamation, first approved April 27, 2021, one week after Gov. Gavin Newsom stood on the dry bed of Lake Mendocino to declare a drought emergency.

Jeffrey DuVall, deputy director of emergency management for Sonoma County, said there could be one more extension of the proclamation in store, though it was premature to say what the staff recommendation to the board would be, with more than a month still to go and many consultations still ahead.

He noted that those whose water source is the Russian River are in a different position than those on the east or west side of the county who depend on other water sources.

“We got a lot of rain, and it filled up our reservoirs, but we still need a little more to bust out of a drought completely,” DuVall said.

There were actually periods during the storms when more rain fell than was forecast, which might have sent Lake Sonoma’s water level over the water supply threshold into what’s called the “flood pool,” transferring management to the U.S. Army Corps of Engineers, said Nick Malasavage, operations and readiness chief for the Corps’ Golden Gate District.

When that happens, the Army Corps’ mission is to ensure there remains sufficient vacant space in the basin to accept additional runoff in the event of future storms — a mission that sometimes requires discharging water in the reservoir to make room.

That hasn’t been necessary at Lake Sonoma, where outflow has remained essentially steady to maintain stable stream flows in Dry Creek and is only slightly less than the runoff still coming in.

At Lake Mendocino, however, the water rose so high that the Army Corps began “high-flow” releases of water Jan. 16. Over the next couple of weeks it discharged about 15,000 acre-feet of water — close to five billion gallons.

Even now, the reservoir holds a little over 80,000 acre-feet, more than its 68,410 acre-foot water supply threshold. (An acre-foot is equal to 325,851 gallons, or about the amount of water needed to flood most of a football field one foot deep. It can supply the indoor and outdoor needs of three water-efficient households for a year.) But under recently revised operational rules developed to ensure available water is maximized, that extra water will be held back until there’s a decent-sized rainstorm is forecast and more room appears needed behind the dam.

Though the same rules are not officially in use at Lake Sonoma, Davis said that up to 19,000 extra acre-feet of water could be held in the reservoir beyond the 245,000 acre-foot water supply threshold under a temporary arrangement with the State Water Resource Control Board.

Davis praised water users for the conservation efforts, which made it possible for the area to endure three years of drought. He said he hoped people would remember those water-efficiency practices because “there’s never enough water to waste.”

“We got very lucky,” DuVall said. “Lake Sonoma and Mendocino came up. We still need to look at how we can conserve water and maintain that, because we don’t know what the future’s going to hold.“

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