Not enough, then too much: North Bay’s recent punishing rains reflect reality of climate change extremes, experts say

It’s a trick of the mind that a few days of rain can so quickly make us forget the statewide drought we’ve endured for three years.

Not even a month ago, Lake Sonoma held the smallest amount of water since its creation in 1983 — a reflection of the region’s paltry rainfall and its water supply deficit

Now, it’s like Water World everywhere. The ground is squishy. Pounding rain has been hurtling from the sky for days. The most ephemeral streams, creeks and rivers run high, with significant flooding along the lower Russian River expected in mere days.

What gives? And where exactly do we stand?

The answer is a little unclear, given the abundance of rain still coming next week alone — 5 to 10 inches in most of Sonoma County expected in at least two storms, forecasters say — and the vast uncertainty about how the rest of the traditional “rainy season” will pan out once the current storms have passed.

It’s obvious that the water supply for much of the state, including Sonoma County and the North Coast, will be greatly improved — a positive trade-off for the pain and expense of last week’s “bomb cyclone” and accompanying rain that claimed at least five lives across the state, including that of a 2-year-old boy who died when a tree fell on his Occidental home.

Lake Sonoma, low enough last month that a mandatory 30% conservation rate was considered, is now on track to be 88% full by Jan. 16.

Lake Mendocino is filling so quickly it will likely require dam releases once it is safe to do so without jeopardizing those downstream.

It’s a jarring turnabout from the months of bureaucratic maneuvering aimed at hoarding every possible drop.

But rebounding reservoirs aren’t the only measure of drought recovery, and a changing climate only means there will be more yo-yoing between weather extremes in the future, experts say.

“If you define drought by surface water levels, then this is going to dramatically alleviate it,” said Daniel Swain, a frequently consulted climate scientist with the Institute of Environment & Sustainability at UCLA.

Many smaller reservoirs around the state are approaching seasonal storage averages, and even larger ones are making critical headway, he said.

But “that’s not a great way to define drought,” Swain said.

It overlooks the impacts of drought on plant life, particularly the stresses on trees and forests, which contributed to wildfire risk.

ABOVE: Highway 128 crosses the Russian River near Geyserville amid ongoing drought May 12, 2022, and on Jan. 6, after a series of torrential downpours have led to flooding.

Aquifers that have been under increased pressure to supply water in the absence of healthy reservoirs also need more time to recover.

“Those take much longer to restore. They recover on much, much longer time scales, for the most part,” said research meteorologist Marty Ralph, director of the Center for Western Weather and Water Extremes at Scripps Institution of Oceanography at UC San Diego.

“Water supply drought is different from landscape drought,” he said.

Jeanine Jones, drought manager for the California Department of Water Resources, said groundwater monitoring even after a very wet rainy season generally doesn’t show significant improvement in a single year’s time.

Jones also offered some “big picture” perspective on the rain that’s fallen in California this season so far.

It’s been a lot in a short time — 6 to 9 inches in most of Sonoma County over the 10 days ending Friday, with much of it arriving midweek last week. That brought the season-to-date total for Santa Rosa to about 108% of normal, according to the National Weather Service. The water season runs from Oct. 1 to Sept. 30 of the following year.

It’s still only the first part of January, and with forecasting refined enough to provide only about a week of highly accurate projections, there’s no way to know if the spigot will just turn off, as has happened before, Jones said.

“On average, half of our precipitation in California arrives in December, January and February,” Jones said. “We’re just a third of the way through normal season. It’s far too early to say where we’ll be in March, which is about the time we’ll be able to take some comfort in our water supply conditions.

“I can’t resist observing,” she added, “that part of the noise and chatter around this is we’ve been in drought for so long, people have forgotten what winter weather looks like.”

In Sonoma County and elsewhere around Northern and Central California, last week’s rain made such an enormous impact in large part because of two drenching storms — Dec. 27 and New Year’s Eve — that saturated the ground, meaning every new inch of precipitation ran immediately downhill toward the closest ditch, stream, creek or river.

About 20% of what falls in the Russian River watershed — a diverse 1,500-square-mile landscape stretching from rural communities outside Ukiah to Jenner on the Sonoma Coast — gets captured by Lake Mendocino, northeast of Ukiah, or the larger, newer, more southerly regional reservoir, Lake Sonoma, near Cloverdale.

The rest contributes to the high water flows that forecasters say will likely push the Russian River over its banks on Monday, reaching an estimated 6 feet above flood stage in Guerneville, or just over 38 feet.

It hopefully won’t reach as high as February 2019, when the river crested at 45.4 feet — the highest level since 1995 and the last time the river flooded before drought gripped the region.

But the seesaw effect has been evident for the past decade, with drought from 2012 to 2016 segueing to the wettest winter on record in 2016-17, with successive storms that sent the Russian River surging over its banks at least four times.

Swain also referenced the record one-day storm of Oct. 24, 2021, which occurred mid-drought and proved to be the bulk of last winter’s rainfall. And then there are the current round of storms.

“Those are warning signs,” Swain said. “With climate change, we’re going to see a lot of these swings back and forth between these two kinds of extremes.”

“Sonoma County,” he added, “has really been one of the epicenters of, in particular, this flood/wildfire whiplash.”

Sonoma County Supervisor James Gore said he was sorry there were so many downsides to the most recent rains after “all of us have been doing rain dances and praying for rain over the last three years.”

But he also said he would continue to rally people around water-efficient landscaping, lifestyles and habits.

“I can be standing at a filled Lake Sonoma and still telling people that they shouldn’t put in lawns and they should plant native species in their yards and they should use gray water,” Gore said.

For many local water managers, there’s an acute focus at the moment on Lake Mendocino.

The water’s rapid climb is poised to force the Army Corps of Engineers, which controls the dam that created the lake, onto a razor’s edge. Projections put the storage level by this weekend above the threshold at which the Corps must consider releasing water from Coyote Dam to ensure it doesn’t reach the spillway.

There’s plenty of room to work with. And under a groundbreaking arrangement between the Corps and Sonoma County, the Army is no longer bound by inflexible rules that require dumping of water as soon as the flood-control threshold is reached.

Instead, under an operational model guided by Ralph’s research with the Center for Western Weather and Water Extremes, the Corps now has the discretion to hold onto an additional 11,650 acre-feet of water through mid-February if it appears the skies ahead will be clear and extra space in the reservoir is not needed.

The new guidelines were inspired by an incident in January 2013 when the Corps released 25,000 acre-feet of water — enough to supply 75,000 households for a year — downstream, not realizing that the rain had stopped and the rest of the winter would be dry.

“That’s half of what we sell a year,” said Sonoma Water General Manager Grant Davis, whose agency provides water to municipalities and other contractors that supply about 600,000 customers in Sonoma and northern Marin counties.

The event generated enough regret and resentment that a new approach was found.

The issue now is that even that extra allowance likely won’t be enough, given the volume of incoming rain expected — assuming it materializes, said Nick Malasavage, chief of operations and readiness for the U.S. Army Corps’ Golden Gate Division, which oversees flood control operations at lakes Sonoma and Mendocino.

But managers have to balance a variety of needs, including water supply and the safety of those downstream who already face significant flood risk.

The Corps and its partners have been working continually to update forecasts and consider next steps, Malasavage said.

“We’ll have to see this day by day,” he said. “We’ll manage the pool accordingly.”

Davis said, “All eyes are watching what’s coming, hoping there will be enough of a break between these two large storms.”

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

Editor’s note: This story has been updated to correct the amount by which the U.S. Army Corps can exceed the flood pool threshold in Lake Mendocino if the forecast calls for dry weather.