Time between storms this winter reduces flood risk on Russian River

The Sonoma County airport rain gauge shows 25.74 inches for the season as of Sunday.

By this time last year 25.83 inches had fallen since Oct. 1, the official start of the water season.

This year, rainfall totals around the region look awfully similar to last year’s, and are even higher this season than last in some locations, like Bodega Bay and Cazadero.

Yet, last winter residents along the Russian River were preparing for flooding on several occasions.

This year? Not so much.

The main reason, experts say, is the breathing room provided by the pattern of storms in the North Bay over recent weeks.

Though it may be hard to recall, the storms that relentlessly pounded the region last winter were largely confined to a 23-day period from Dec. 26 to Jan. 17, during which 36 inches fell in the hamlet west of Healdsburg known as Venado, for instance.

While storms have delivered significant rainfall this winter, breaks between them have allowed stream and river levels to recede enough before each onslaught to keep the Russian River within its banks, except for minimal flooding where Highway 175 crosses it in Hopland.

“This year, they’ve just been spaced out,“ said Chris Delaney, principal engineer with the Sonoma County Water Agency, known as Sonoma Water. ”The distribution has just allowed flows to recede and the watershed to dry up a bit before we receive the next event.“

What matters, said Nick Malasavage, chief of operations and readiness for the U.S. Army Corps of Engineers’ San Francisco District, which manages lakes Sonoma and Mendocino, “is the intensity, the distribution and how recently did it last rain? Because you could have five inches on one day, but if it was after two weeks of sunny skies and it was followed by two weeks of sunny skies, it doesn’t necessarily come with trauma.”

The Russian River watershed is considered a “flashy” system, meaning its topography and size cause it to react quickly when heavy rain comes. That means differences in the amount of rain and where it falls can have an outsized impact.

And as it happens, this year’s storms have been less extreme in the volume of moisture they’ve brought, Delaney said.

Most atmospheric rivers this year were rate Category 1 to Category 3, he said. Last winter, they were Category 2 to Category 4, dumping more rain per storm.

“A lot of our events have been more to the moderate side but not the really big extremes of last year,” National Weather Service meteorologist Braydon Murdock said. “Those extremes put more pressure on main stem rivers. We’re not seeing the numbers that we saw with individual rain events last year.”

A greater abundance of rainfall in the northern part of the region last winter also means river flows already were elevated in the Russian River’s upper reaches and kept accumulating runoff and inflow from tributaries as the water moved through the system, Murdock said.

But even last year, despite several occasions on which minor flooding was forecast in the lower river corridor, those communities were spared. It helped that the first rounds of landed on soil so parched after years of drought that much of it was drunk in by the landscape.

“There were a few points — I want to say right before (Martin Luther King Day) — where I think folks were holding their breath,” Malasavage said, “but I don’t remember River Road ever closing … Those few days where there was the potential (for flooding) luckily the potential wasn’t realized.”

The disparity between this year and last highlights the unpredictable effects of an El Niño climate pattern on this part of the coastline, as well, said Dalton Behringer, another meteorologist with the National Weather Service.

Though it has resulted in huge rainstorms in southern areas, like Los Angeles and San Diego, as expected, it has delivered less intense rain to the North Bay this year than last year’s La Niña

“There’s this notion that El Niño is supposed to give us more rain, which is not entirely true, and the juxtaposition of the two years, this year and last, kind of show that,” Berhringer said. “It’s not a slam dunk. Last year was a strong La Niña, and we got more rain.”

There is still time for more winter storm activity this year, but the so far beneficial rainfall — as distinct from the battering winds that have caused damage around the region — have filled lakes Sonoma and Mendocino full to the brim, with a few clear days ahead to begin measured releases, “once flows in the river have receded,” Delaney said.

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