Wine Lovers: Relax, Study Suggests Calif. Grapevines Can Weather Searing Drought

The drought could be crippling, but the wine will be good.

That is the happy conclusion of a study published today in the journal, Science. It turns out that the grapevine is hardier than anyone thought.

Scientists who looked at vineyards in California's Napa Valley and the Bordeaux region of France found that in times of drought, the grapevine’s resistance actually increased as the season progressed.

The study, conducted over a period of ten years, found that the grapevines were not at risk of dying from “even very dry conditions.”

That means farmers may not need to water their vineyards as much as previously thought during a dry spell.  It also could mean better-tasting wine.

"One of the triggers of ripening occurs when  stress is present such as a dry spell," says Paul Skinner, a co-author of the study and a vineyard consultant at Vineyard Investigations. "It serves to slow down the growth of the vine vegetatively and when the vine stops growing, that is directly connected to the ripening of the fruit."

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The study sets the practical limits of when grapevines die without water, says Skinner. "This is about trying to figure out how to manage vines during periods of drought. We need to know what these limits are in order to manage risks."

The findings are a boost for California vineyards, which produce nearly 90 percent of all American wines.

Big Business

The wine sector is an economic powerhouse for the state and threats stemming from climate change could spell serious trouble for California's economy.

According to a report issued in 2016 by the Wine Institute, the industry contributes $57.6 billion annually to the local economy and employs about 325,000 people.

The Golden State's renowned vineyards also attract some 24 million tourists annually, generating $7.2 billion in revenue.

During severe droughts, plants often die from embolism. It occurs when plants are deprived of water, causing tension in the plant as it starts to convert water into gas. The resulting air bubbles impede the passage of water within the plant, causing it to increase in thirst and potentially die.

“When plants are well watered, they will never experience embolism," Skinner told KQED. "It’s a result of extreme drought. And a purpose of this study was to quantify what the threshold is for mortality in a grapevine during a drought."

Though total precipitation might not decrease with California's changing climate, scientists say to expect more severe droughts when they do occur. The study looked at what levels of drought would be enough to cause a degree of embolism sufficient to kill grapevines.

“We looked at the level of drought and we looked at Napa and found that their vines never reach that level,” says Gregory Gambetta, a professor of viticulture at Bordeaux Sciences Agro and the study's principle investigator.

And as the world grapples with climate change, knowing what these thresholds are is of critical importance to farmers.

“As the climate is changing, we can determine, 'What are the tolerance levels of these plants and will they endure?'" explains Gambetta. "Will vines survive and bounce back?”

Saving Grapes

Skinner says the study will also allow farmers to adopt techniques to weather climate change.

“It might prove to be very valuable for land owners who do not want to lose their physical vineyards and plant something else," he suggests. "I think it will lead to more refinements in what we do, rather than major changes.”

Gambetta adds that vineyards are normally productive for twenty to forty years and require a significant amount of financial investment. The study's findings suggest that farmers might not have to abandon their crop during a dry spell.

“In California, during these drought periods," he says, "farmers regulate the amount of water they get and sometimes they make decisions to essentially whip out vineyards, thinking they will probably die anyway. So there is question of, 'Did they have to?'”

Gambetta cautions, however, that the study’s findings do not mean farmers should stop watering their vineyards.

“It simply sets thresholds that we did not know before, that we could not quantify precisely," he points out. "Now, we can say that these are the levels of stress that vines can endure during a period of drought. That sets a bar for farmers.”

"We found that the vines were very resilient and we now know what range we are operating in," adds Skinner. "Hopefully we can find ways to save water by adopting some of the information in this study as a guide."

And while researchers still have some important questions concerning to what extent vines can repair themselves and recover, farmers now at least have actual numbers to work with when determining how to ration resources.

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As for how you ration your wine, you're on your own.

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