Areas of Sonoma, Napa, Mendocino, Solano, Lake counties now considered to be in ‘exceptional drought’

Nearly all of Sonoma and Napa counties and large portions of neighboring counties are now classified by the U.S. Drought Monitor as “exceptional,” the worst of five categories for intensifying drought and a sign of deteriorating conditions in California’s North Bay region.

Also affected by the designation are areas of Mendocino, Lake, and Marin counties bordering Sonoma County, as well as western parts of Contra Costa, Solano and Alameda counties.

The new classification comes as reservoir levels continue their decline and domestic and agricultural users along the upper Russian River brace for notices expected next week curtailing their rights to divert water.

The designation appeared in the weekly map published Thursday by the Drought Monitor team, a partnership of the National Drought Mitigation Center at the University of Nebraska-Lincoln, the National Oceanic and Atmospheric Administration and the U.S. Department of Agriculture.

The situation has not been this grim since the latter half of 2014, halfway through a five-year drought that tested the region’s mettle and reset expectations around water availability. But in that case, the “exceptional drought” rating came into play in late July, not mid-May.

“It’s just entering the dry season out there,” said Adam Hartman, a meteorologist with NOAA’s Climate Prediction Center in Washington, D.C., who authored Thursday’s map, “and given the antecedent conditions, it’s not looking promising. We really feel for you all out there.”

Even at a time when much of the western United States is experiencing some degree of drought, the North Bay stands out as a lone island of “exceptional drought” in Northern California, though “exceptional” conditions also prevail in Arizona, Utah and southern Nevada, spilling into California’s Inyo, Tulare and several neighboring counties.

Two years of very low rainfall in and around Sonoma County have left the region beyond parched. Its soil moisture is extremely low. Stream flows are dwindling or have dried up altogether, which has left vegetation in severe stress, and groundwater levels notably diminished. All of those factors are taken into account in classifying the degree of drought, Hartman said.

Also noted, he added, are reports of dried up stock ponds and pastures that have forced some dairy ranchers to truck in water or buy forage for their cattle. Water management, satellite data and ground-based measurements are also monitored.

Hartman said experts use all of these factors to "get an idea of how conditions are on the ground ... of what’s really going on to try to consolidate it into our best estimate of the drought depiction and what it should be.”

Locals have grown increasingly aware over recent weeks of just how bad the months ahead look, given two successive seasons of rainfall so low that combined they barely equal an average year.

And, though consumers above the confluence of Dry Creek are under order to conserve water and significant restrictions already are in place in many rural areas, storage in Lake Sonoma has now slipped to 59% of capacity, water officials said. In addition, the smaller and older reservoir, Lake Mendocino, is at 41½% — diminishing at a faster pace than anticipated, in part through evaporation.

The cities of Healdsburg and Cloverdale have adopted mandatory rationing. While other municipalities and water providers around the area — except Sonoma — have imposed voluntary conservation measures, though city residents should be abiding by a countywide 20% voluntary conservation strategy approved last week by Sonoma County supervisors.

The Sonoma City Council is expected to consider a local 20% voluntary conservation measure on June 7, Interim City Manager David Kiff said.

By then, the county water agency may already have heard back from the State Water Resources Control Board about a temporary urgency change petition submitted last week.

It seeks permission to lower in-stream flows in the Russian River below those usually required for imperiled salmon and steelhead trout in order to preserve water supplies in Lakes Sonoma and Mendocino.

Sonoma Water, which provides water to more than 600,000 consumers in Sonoma and northern Marin counties, would reduce diversions from the river by 20% as part of the agreement with the State Water Board and have a fifth less water to sell to suppliers. This would set the stage for mandatory conservation measures around the county.

Meanwhile, water rights holders above Healdsburg and the point where Lake Sonoma releases augment those from Lake Mendocino could hear, as early as Tuesday, that they no longer can exercise their right to draw water from the Russian River, according to Erik Ekdahl, deputy director of the Division of Water Rights for the California State Water Resources Control Board.

Though similar action is soon expected in other California watersheds, it is happening first in the Russian River watershed, he said.

A weekslong effort to arrive at a cooperative, voluntary sharing agreement between users with different water right priorities laid solid groundwork for the future, he said, but there was simply not enough water supply for those with stronger rights to share with those whose rights were newer.

“Even now we’re looking at (reservoir) levels, and they’re depleting faster than expected,” Ekdahl said, “and it’s going to be really hard with so little water to work with. What we have made good progress with is setting things up for the future, and all the conversations we’ve had, I think is time well spent.

“But this year is such an unusual year,” he said. “Not every year is going to be like this. There will be other years that are dry but they are not quite so bleak.”

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