California vineyards can still produce great wine even with limited water supply and droughts

Two new studies from UC Davis reinforce the long-held belief that water-deprived vines can produce high-quality wine grapes, when managed with care.

“If you look at that at 20,000 feet, people are saying agriculture will have to contract,” said Kaan Kurtural, co-author of the studies and viticulture and oenology specialist at UC Davis, referring to the potential effects of mega-droughts on the condition. “I can’t think of a better crop than wine grapes grown in California now with the water restriction or lack of water. “

Based on research from a test Cabernet Sauvignon grape vineyard in Oakville, Napa County, during a wet 2019 and a dry 2020, the first study, published earlier this month in Frontiers in Plant Science, showed that wine growers can cut red grape irrigation by 50% while still getting good quality and yield. A related study, published last week in the journal Food Chemistry, showed that such reduced irrigation actually increased the amount of pleasant aromatics in Cabernet Sauvignon grapes and decreased the unpleasant ones.

The amount of water used by California winemakers varies from region to region, but coastal wineries such as Napa and Sonoma typically use half an acre of water, which means enough water to cover each acre with half a foot of water per year. – while interior vineyards use 1 acre foot. Nut trees, on the other hand, need around 4 acres, Kurtural said.

Napa and Sonoma counties typically receive 20 to 30 inches of rain; this last rainy season they got 6 inches. Despite this, the Oakville Trial Vineyard’s yield this year was similar to that of 2019 and 2020. Additionally, Kurtural’s group found that using a smaller amount of water improved the health of the plant. soil in a way that could mitigate the effects of climate change by building more beneficial fungi in the soil compared to more moist soil.

“What it shows is that when it comes to environmental sustainability, wine grapes use very little water but can produce good quality wine as well as sustainable yields,” said Rhonda Smith, Advisor Emeritus. in viticulture at UC Cooperative Extension, which was not involved. in the study.

Many growers fear that ever-rising temperatures and more frequent droughts associated with climate change will force them to add additional irrigation – if they can find it, Kurtural said. But research shows growers can use half the water they would expect to need based on a technical measurement called evapotranspiration, or the amount of water lost through evaporation in the soil and canopy. . Instead of replacing 100% of that water, they can only replace 50% while achieving good quality and similar yield, according to the study.

Ultimately, that means growers in Napa and Sonoma could stick to the usual half-acre-foot and still do well even as temperatures rise and rain decreases.

“I agree – quality can always be maintained with less water,” said Oscar Renteria, owner of Renteria Vineyard Management, which manages 63 plots in Napa Valley for 38 wine growers. “So far this year has been an incredibly high quality year. He will compete with the best.

However, Renteria and her team had to be selective about water use, sometimes giving more to vineyards with premium fruit and less to others. They spent more money on soil monitoring probes and other precision tools and invested $ 25,000 to buy water for a vineyard, he said.

He now wonders if he has watered too much in the past.

“When you have it, you use it. When you don’t, Mother Nature has a way to teach you a lesson, ”he said. “Based on this year’s experience, we can definitely see that we could get by with less water.

Many believe that dry farming, or farming without irrigation, could be a solution to the ongoing droughts, but this style of farming is also difficult without rain.

“If I had water I would give it to the vines this year,” said Stu Smith, co-owner of Smith-Madrone Vineyards & Winery in St. Helena, which normally operates dry farms. However, due to the lack of rain this year he ended up giving the vineyard 6 gallons of water, which is not much. He still sees signs of good quality during the harvest.

“All else being equal, we should have a very dark and flavorful red wine crop this year,” said Smith, who points out that wine grapes have been dry grown for most of their history.

Although the quality is good this year, Renteria and other winemakers are still unsure how their vineyards would react with a drought lasting several years.

“This climate is changing before my eyes,” Renteria said. “It’s a way to get attention. I am not relaxed about it.

Tara Duggan is a writer for the San Francisco Chronicle. Email: tduggan@sfchronicle.com Twitter: @taraduggan