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El Niño forecast boosts hopes for wet season on North Coast

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Battered by a historic drought that has fed raging wildfires, shrunk reservoirs and prompted water curtailments and conservation mandates, Californians are yearning for relief.

It can only come from the skies, and now, with winter on its way, the question on the minds of more than 38 million Golden State residents is: Can El Niño, the weather phenomenon named for the Christ child, deliver meteorological salvation across the land, from the arid south to the normally damp north?

For the North Bay, where that answer is still highly anticipated, a shortfall on the wet forecast may not portend an immediately deepening disaster, as it could for much of the rest of the state.

The region draws its water from the Russian River and local wells, independent from the Sierra Nevada snowpack — the lowest in recorded history last winter — and the state’s major reservoirs, now 70 percent to 90 percent empty.

The North Bay’s major reservoir, Lake Sonoma, with a two-to-three-year supply when full, remains at more than 70 percent of its capacity.

Just an average amount of rainfall over the next six months in Santa Rosa — about 36 inches — would go a long way toward topping off that supply and other local reservoirs, significantly easing drought in the region, if not ending it, said managers of the Sonoma County Water Agency, the primary source of water for 600,000 North Bay customers.

“If we could get that, we’d be doing OK,” said Pam Jeane, the Water Agency’s assistant general manager.

To make up for its accumulated deficit from the four-year drought, Santa Rosa would need an additional 30 inches — a soaking that would flirt with or break records but also risk significant damage if it came in a single season.

Water managers are wary of that possibility.

“It would be great if we could get more, but we don’t want it all at once,” Jeane said.

In Valley Ford, beef and cattle rancher Joe Pozzi would like rain to fall soon, greening his pastures while the soil is still warm and continuing through spring, replenishing farm ponds. That would be ideal, he said, “but at this point, we’ll take whatever we can get.”

As it stands, El Niño is muscling up in the Pacific Ocean around the equator, renewing the prospect of a wet California winter. While that forecast fizzled last year, this year there is a 95 percent chance that El Niño will continue through the winter before gradually weakening in the spring, according to the latest federal forecast.

“El Niño hype is in full swing,” said Jan Null, a consulting meteorologist, referring to advertisements urging people to buy ski passes and make sure their roofs are ready for winter.

El Niño ‘misunderstood’

There’s some basis for anticipation, given that the El Niño is on par with California’s last very strong event, Null said, which delivered 167 percent of normal rainfall statewide and 154 percent to the North Coast region from Marin County to the Oregon border in 1997 and ’98.

But El Niño’s track record — with 23 events since 1950 in California — is mixed. A dozen have been classified as weak, six as moderate and only five as strong or very strong, with an average yield of just 105 percent of normal rainfall. The likelihood of heavy rain increases with the strength of an El Niño, but two of the three strong events delivered below-average precipitation on the North Coast while a weak event in 1994-95 dropped 143 percent of average rain, the fourth highest rainfall ever.

El Niño is “misunderstood,” said Null, a former National Weather Service meteorologist.

Nor is it the only path to plentiful rain. The February 1986 flood that inundated Guerneville and Monte Rio came during a La Nada, nicknamed after the Spanish word for “nothing,” meaning it was neither an El Niño nor a La Niña, which is associated with subnormal precipitation. The deadly Eel River flood of 1964 came during a weak La Niña.

Both were the product of an atmospheric river, a prolonged flow of warm, moist subtropical air responsible for most of California’s flooding, Null said.

Two such storms brought much of last winter’s rain: about 6 inches in Santa Rosa from Dec. 10 to 12 and 4 inches from Feb. 6 to 9. After the February storm, fewer than 2 inches of rain fell and the city ended the rain year on June 30 with 25 inches, well below normal.

Currently, Santa Rosa’s four-year rainfall deficit is at just over 30 inches, the fourth worst since 1902, Null said. The drought that started in 1975 — and inspired slogans for bathroom etiquette like “if it’s yellow, let it mellow” — left the city with a 43-inch deficit, the biggest ever.

Even a little rain would help

No one wants a deluge, and it wouldn’t take one to make a big dent in the drought, according to Tom Di Liberto, a meteorologist at the National Weather Service’s Climate Prediction Center. In a blog at Climate.gov titled “How deep of a precipitation hole is California in?” Di Liberto said much of the state is missing at least one year’s worth of precipitation over the past four years.

The amount varies widely by region, from the North Coast, the state’s wettest, at 50 inches in arrears, to the arid southeast with an 8-inch rain deficit. The South Coast, including Los Angeles, faces a 32-inch deficit, which amounts to nearly two years worth of rain. That deficit is “not so much a hole as a giant chasm,” Di Liberto said.

He also defined a drought-ending threshold as getting out of the bottom 20 percent of five-year accumulated rainfall, which also varies by region. The North Coast needs 135 percent of normal rainfall by the end of September 2016 to meet the threshold and would need the 11th wettest October-to-September period since 1928 to get there.

“It’s not out of the realm of possibility during a strong El Niño,” he said in an interview. “It’s still a lot to ask.”

The Central Coast, South Coast and the San Joaquin Valley all need more than 190 percent of normal rainfall over the next year to move out of drought. For the Central Valley — California’s agricultural heartland — that would require the wettest water year on record.

Mike Anderson, the state climatologist, said past wet seasons that ended multiyear droughts had about 150 percent of average rainfall and about 150 percent of average snowpack. Beating a drought means refilling reservoirs through winter storm runoff augmented by spring runoff from the snowpack, as well as restoring groundwater losses, and the latter often requires “multiple wet years,” he said.

Based on the strengthening El Niño, the odds of a wet winter across the state are “better than 50-50,” said Doug Carlson, a Department of Water Resources spokesman, but the agency is still promoting water conservation.

“One wet winter alone won’t be enough to declare victory over this drought,” he said.

Where rain lands matters

There’s also a key question of where the rain comes down, regardless of El Niño.

The Climate Prediction Center’s U.S. Winter Outlook forecasts above-average rainfall for December to February in all but the northernmost corner of California, with a similar band sweeping across the south, some of the plains, across the southeast and arcing as far north as New Hampshire.

But the probability of a soggy California winter is highest — over 50 percent — in Southern California, then drops to the 40 percent range in Central California up to the Bay Area, and fades to 33 to 39 percent a little north of the Golden Gate.

The latest U.S. Seasonal Drought Outlook, also by the Climate Prediction Center, draws an east-west line bisecting California at San Francisco Bay. To the north, the drought is expected to persist or intensify through the end of January; to the south, across Central and Southern California, parched conditions are expected improve.

The Bay Area is typically the borderline for rainfall rewards from weak and moderate El Niños, while strong and very strong events tend to push the wet line closer to Oregon, Null said. The current El Niño signal is stronger for the central and southern parts of the state, compared to the northland, Di Liberto said.

And it matters a lot where water comes down in California.

Heavy rain down south is likely to cause chaos, as it did two weeks ago in the Bakersfield area, where a flash flood unleashed what witnesses called a “raging river of mud” that terrified and trapped motorists. It also means little to the millions of Southern California residents who get most of their water from snowpack that feeds the Colorado River and Northern California reservoirs.

Heavy rain and snow up north would fill the likes of Lake Shasta, the state’s mega-reservoir, now holding less than one-third of its 4.5 million-acre-foot capacity. “That’s where we capture it and convey it,” Carlson said.

Lake Oroville on the Feather River is less than 30 percent full and Trinity Lake on the Trinity River is just over 20 percent full, both sporting massive bathtub rings of bare earth.

In contrast, the North Bay’s major reservoir, Lake Sonoma west of Healdsburg, holds more than 70 percent of its 245,000-acre-foot capacity, while smaller Lake Mendocino near Ukiah is 40 percent full. The two reservoirs benefited from decent rainfall in the past year, measured at 27 inches in the Ukiah basin and 24 inches in the Santa Rosa basin, according to the Sonoma County Water Agency.

“It’s not fabulous,” said Jeane, the agency’s assistant general manager. “We would love to see more water in the reservoirs now.”

But Lake Sonoma, the result of a $330 million dam project completed in 1983, affords the region a formidable backup when full, officials said.

Drought in the North Bay has officially been classified as “severe,” an ominous category, but one several grades less serious than the “exceptional” drought that has taken hold across nearly half of California, according to the latest forecast by the U.S. Drought Monitor.

But just what it takes to beat the drought on the ground, as opposed to a government document, is unclear. The Department of Water Resources hasn’t put any numbers on it, Carlson said.

The Water Resources Control Board will consider local conditions and winter precipitation in determining whether to renew state water conservation mandates next year, said Max Gomberg, a board spokesman.

Conservation mandates

Heeding Gov. Jerry Brown’s demand for a 25 percent reduction in water consumption, Californians this summer saved more than 600,000 acre-feet of water, putting the state more than halfway toward meeting the goal of saving 1.2 million acre-feet by February. An acre-foot is about enough water to fill a football field a foot deep, or supply 893 gallons of water a day for a year.

Whether the governor’s conservation mandate will be renewed next year has not been decided, a state water board official said.

No exemptions would be granted to a region, but local water suppliers will qualify, as they did this year, for a lower conservation target based on the per capita water consumption of their customers, he said.

If Lake Sonoma and Mendocino were full, Jeane said the region would be drought-free in terms of Russian River surface water supply, but groundwater would likely take much longer to recover.

Rain can’t come soon enough for Cal Fire, which battled a pair of wildfires that scorched a total of 145,500 acres in Lake County, feasting on brush so dry it startled veteran firefighters. And if the rain stretched into spring, “that would be awesome,” Cal Fire spokeswoman Suzie Blankenship said.

Timing is also critical to reservoir managers, since runoff from midwinter storms often must be released and allowed to flow to the ocean to preserve flood storage capacity in the event of spring downpour.

Pozzi, the Valley Ford rancher, said that last winter’s storms filled stock ponds, but the virtual cutoff after February was a problem as spring turned to summer.

Season-long, intermittent rains over two years would be his preferred way to banish the drought over a single-season soaker that wreaks havoc.

“If we got 80 to 90 inches of rain (this winter) we’d be in trouble,” he said. “It’s that happy medium we’re all looking for.”

You can reach Staff Writer Guy Kovner at 521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.

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