Should California winegrowers be worried about El Niño?

Winter and spring storms can bring a deluge of rain to Sonoma County, swallowing vineyards and turning low-lying areas into a network of lakes and ponds.

While the sight of a flooded vineyard may be worrisome, the dormant grapevines typically remain unaffected, their roots requiring little oxygen or nutrients while growth is suspended.

But what happens if the rain keeps coming?

That is the question facing local winegrowers this fall after the National Oceanic and Atmospheric Administration (NOAA) issued a June 11 advisory predicting a potentially record-breaking El Niño in the coming months.

El Niño is a naturally occurring climate pattern that develops when ocean temperatures in the central and eastern tropical Pacific rise above normal, influencing weather around the world.

According to NOAA’s U.S. Winter Outlook, issued Oct. 15, El Niño is expected to bring warmer-than-average temperatures and abundant rainfall to Northern California from December through February.

“The current conditions over the Pacific Ocean and those being modeled this winter tilt the odds towards having a much wetter-than-average winter (in California), with the potential for very strong events, such as atmospheric rivers,” said Gregory Jones, an atmospheric scientist and wine climatologist at Abacela winery in Oregon. “That could bring too much rain, too fast, and create flood conditions.”

Too much of a good thing

Heavy rains can benefit vineyards by replenishing aquifers and refilling reservoirs, wells and ponds. Prolonged flooding, however, can pose substantial risks.

“If the soil remains flooded with no air pockets by spring, the grapevines will have difficulty getting oxygen to their roots,” said Christopher Chen, a climate-adaptive viticulture adviser at University of California Agriculture and Natural Resources. “That could lead to failed bud break in the spring and major crop loss.”

Chen points to another potential consequence of sustained rains.

“In years with heavy flooding, the soil can become depleted in nutrients, like nitrogen and potassium, which are both necessary in early spring to get the vines going,” said Chen, who specializes in vineyard stress tolerance on the North Coast. “If the grapevines haven’t been fertilized, all their nutrients can wash away.”

From vineyard to lake

At Balletto Vineyards in the Russian River Valley, seasonal flooding is a familiar sight.

During heavy winter storms, runoff from the surrounding hills collects in low-lying areas of the Laguna de Santa Rosa watershed and spills onto nearby agricultural land, including Balletto’s Occidental Road and BCD vineyards.

As the Russian River rises, flooding can intensify, with high river levels slowing drainage from the Laguna and causing water to back up across the floodplain.

“If flooding only lasts a few days, we typically don’t have any issues,” said John Balletto, founder of Balletto Vineyards. “What would really hurt the vines is the buds going underwater after budbreak. If that happens, we would have zero crop because the buds would likely fall off.”

Despite the potential risks, heavy rains help irrigate the vines deep beneath the soil, which is beneficial in the long term, added Balletto.

To prepare for impending storms, his team is currently installing erosion controls in flood-prone areas.

“We’re seeding cover crops right now and making sure any loose items are tied down or taken out of the vineyards,” he said. “We prefer to seed every other row because it helps keep the ground stable. My hope is El Niño won’t have a damaging effect on Sonoma County or its residents.”

The risk to spring flowering

In March, a record-breaking heatwave triggered early bud break, followed by wind and rain that disrupted pollination. The result was smaller grape clusters with fewer berries, contributing to one of the earliest and smallest harvests in recent memory.

Whether El Niño will produce similar conditions in 2027 remains to be seen.

“In Sonoma County, we’re used to having these nice, pleasant springs that aren’t too hot. But I expect to see the temperatures get hot relatively fast,” Chen said. “That could promote insects and powdery mildew with all the extra moisture in the soil from the rain.”

Treating powdery mildew often requires tractor-mounted sprayers. Driving heavy equipment over waterlogged soil can compact it, damaging its structure and reducing its ability to absorb water and support healthy root growth.

“If the soil is still soaking wet in the spring, they’ll be in a predicament,” Chen said. “It’s either compact the soil with a tractor or wait until it dries out and hope the fungal pathogen doesn’t spread.”

Preparing for runoff

At Jackson Family Wines in Santa Rosa, vice president of farming Scott Welch oversees about 4,000 vineyard acres across the North Coast. The company’s founder, Jess Jackson, favored planting vineyards on mountains and hillsides, giving Welch extensive experience managing erosion and runoff.

“We regularly get anywhere from 25 to 50 inches of rain across the North Coast each winter, so our standard procedure is being ahead of the game and doing everything we can to prevent erosion,” Welch said. “From straw wattles to cover crops to clearing drainage ditches and culverts — it’s all part of our responsibility and commitment to take care of this land, regardless of long range weather forecasts.”

Jackson Family Wines has largely continued its usual operations leading up to winter, but Welch took a precautionary step in mid-July, instructing his team to stop replenishing some reservoirs in anticipation of El Niño.

“That will allow us to capture more rainfall and store the water that might otherwise flood into rivers or tributaries,” he said. “Our reservoirs are drier than normal right now. But that’s because we’re better prepared.”

Predicting whether heavy rains will affect the size and quality of next year’s vintage is difficult.

If the wet weather persists into spring, as it did in 2026, it could disrupt flowering and pollination, potentially resulting in a smaller, less uniform crop. But if most of the rain falls in December and January, well before bud break, the additional moisture could support vigorous vine growth and larger berries.

“I work with a lot of winemakers, and they would much rather see a wet winter than be in a four-year drought,” Welch said. “You’re going to have more leaf growth, which protects the berries from birds and sunburn during summer heat spikes. There is a better chance you’ll end up with something spectacular.”

Sarah Doyle is the wine and beverage reporter at The Press Democrat. Send her story tips at sarah.doyle@pressdemocrat.com.