Strategies to Adapt to Climate Change
By David Eddy, Editor, American Fruit Grower
The change has been slow, but steady, seemingly inexorable. Rising temperatures for wine grape growers can perhaps best be seen in the statistics for two of the world’s premier wine growing regions, says Kaan Kurtural, the President of Kurtural Vineyard Consulting in Davis, CA. Though an ocean and a continent apart, since 1980, both Bourdeaux, France, and Napa Valley, CA, shot up from approximately 2,000 F growing degree-days to nearly 4,000 degree-days.
“They used to be Cool Region 2, but the increases happened very quickly,” says Kurtural, who retired two years ago as an Associate Professor in Cooperative Extension from University of California, Davis. “In the last 40 years we have changed the climatic index by two tiers in accumulations of growing degree-days.”
These (formerly) cool-climate regions are certainly known for producing fine wines. However, concerns about rising temperatures were assuaged by the rising sugar content — the Brix, he says. Overall, the effects on the quality were actually positive. At least until now.
Growers in those regions continue to fare well, producing grapes for ultra-premium wines. In fact, the only category of wine sales that was up in 2023 over 2022 were bottles selling for at least $100, increasing 7%.
But it’s getting tough retaining that quality as it gets warmer and warmer, says Kurtural, who adds that it’s not the heat per se, it's the amount of UV and Near Infrared light.
“That’s what is damaging the grapes,” he says. “The leaves can moderate their temperatures, but the berries cannot. That’s where the damage happens.”
In Napa and Bordeaux viticulture has successfully adapted to a drastically changing climate thus far, but fruit-based metrics raise concerns that we are approaching the tipping point. Kurtural says that point is reached when the grapes are no longer producing the necessary compounds, such as anthocyanins, to reach high quality.
“They’d be just sacks of sugar water — no color to them,” he says. “The tipping point hasn’t been crossed but it’s close.”
It was eye-opening to use, and then we realized we could design trellises to protect the fruit. That was a breakthrough point in our work.
U.S. growers have an advantage in that unlike many other countries, the U.S. generally has the water, and perhaps most importantly, the energy to deliver the water. But growers wanted to do something to protect their grapes, and Kurtural says he and his fellow scientists advised shading them. It was a stop-gap measure, but it worked. The scientists were then able to identify some thresholds for grapes. Light and temperatures come hand and hand in the form of heat energy, after all.
“It was eye-opening to use, and then we realized we could design trellises to protect the fruit,” he says. “That was a breakthrough point in our work. Trellises can be expensive, but they can provide protection from these untoward weather events.”
Part of the problem was that in the past, wine grape growers wanted all the sun they could get. After all, that was what the researchers told them to do for the last 30 years. But as temperatures rise, researchers realized the grapes were getting too much sun.
Protecting the grapes by going back to the future, scientists realized the old single high wire (SH), as well as the high quadrilateral (HQ) training systems worked extremely well to shade the grapes — but critically, not too much. A study Kurtural co-authored, “Adapting Wine Grape Production to Climate Change Through Canopy Architecture Manipulation and Irrigation in Warm Climates,” demonstrated the advantage of the SH and HQ systems over the vertical shoot positioning (VSP) systems. VSP is better for cooler climates and so came into favor, but in warmer regions the grapes got too much sun, producing grapes low in important components, such as total soluble solids (TSS).
Don’t over-irrigate to combat climate change. Just make sure the vines can use the water effectively.
“Our results indicated that SH and HQ trellis systems could enhance the efficiency of grapevine canopy in promoting TSS accumulation and yield as well as higher capacity for flavonol and anthocyanin accumulation in berry skins with less chemical degradation compared to the traditional VSPs,” the study concluded.
Growers often ask why they can’t just use more water to cool things down, Kurtural says. Grapevines are different than other fruit crops, in that restricting water has nice effects on wine grapes. He and his colleagues found that cutting irrigation amounts to 50-80% of the current recommended levels is a “sweet spot” for growers.
“Don’t over-irrigate to combat climate change,” he says. “Just make sure the vines can use the water effectively.”
For improving efficiency, Kurtural advises growers to think creatively, and consider new technological advancements. For example, he’s long been suspicious of the use of biostimulants. However, he has found in several trials that biostimulants do increase the rates of photosynthesis in the leaves.
“I was very skeptical,” he says, before adding with a chuckle: “but it actually works!”
Another reason for growers to be optimistic is that the HQ and SH systems — which researchers have found to provide far better sun protection for the grapes than the fashionable VSP systems — are much more amenable to mechanized vineyards. A longtime goal among many researchers is the “touchless vineyard,” in other words, entirely mechanized.
A simple solution to climate change for a California grower would seem to be to start farming at least some vineyards in northern latitudes. There have long been rumors of Golden State growers buying land in Washington state, for example. But Kurtural doesn’t believe we’ll see it on a widespread basis because of the expense and the lack of a widely available labor force.
“No, growers are in the business of making money,” he concludes. “They will use tech. Technology is on our side in the U.S.”
