Four experts discussed the latest approaches to water management in a drying world at Napa Green’s recent RISE Wine and Climate Conference held in Napa on April 29, the first of a six-day series of talks, demos and panels on wine and climate held at Charles Krug Winery in St. Helena.

Is the solution changing rootstocks? Better canopy management? Vineyard sensors and AI-enabled data systems to analyze the data? Refining cover crop choices? Better grafting?

Global water scientist Dr. Jay Famiglietti, Global Futures professor in the School of Sustainability in the College of Global Futures at Arizona State University, moderated the panel “Is Water the Solution to Heat Stress?” The panel also featured another leading scientist, Beth Forrestel, Ph.D., assistant professor of viticulture and enology at UC Davis, who focuses on drought and heat responses in winegrapes as well as ways to mitigate climate change impacts in viticulture.

Vineyard experts Rob Whyte, chief of operations at Napa-based Renteria Vineyard Management (where he oversees 2,000 acres of vines), and 25th-generation French vigneron and artisanal vineyard consultant Philippe Coderey of Roots Vineyard Consulting in Sebastopol also participated.

Known first for his pioneering work using NASA satellites to document declining groundwater supplies in California, Famiglietti painted a distressing picture of decreasing water availability. He has written that California’s Central Valley, a prime wine-growing region, is among the three fastest-depleting large aquifer systems worldwide.

Though the Central Valley is a crisis flashpoint, he said, “It’s not just the United States. It’s not just California. It is really happening around the world.”

He questioned whether the Sustainable Groundwater Management Act would be effective enough in recharging water supplies, which are also needed for food production.

Recharge periods are not sufficient to replenish aquifers, which are losing water reserves, and California has been losing water for decades, mostly groundwater, he said.

Forrestel said the trends are indeed global and that growers worry the most about increasing extremes, including the declining number of growing degree days due to rising temperatures as well as heat spikes.

“…for the first time ever last year, the OIV (International Organization of Vine and Wine) attributed the decrease in wine production not only to economic factors but also to extreme events, including heat,” she said.

Forrestel showed data that the number of growing degree days in Napa declined from 2,035 in 2015 to 1,606 in 2023 as temperatures warmed. Brix and anthocyanin levels have correspondingly skyrocketed (as shown in the cluster graphs above) and showed the following slide:

Water alone cannot fix the problem, she said.

Forrestel advocated using traditional heatwave mitigation techniques, such as:

• Irrigation management
• Misters and sprinklers
• Shade cloth
• Shifting row orientation, vine height and training (providing shade)
• Vineyard floor management (cover crop choice and management, maintaining cover throughout the season, short- and long-term impacts)
• Considering phenology and timing of harvest
• Cultivar choice

Tillage is another concern, she said. “The hotter it gets, the greater difference you see between tilled and untilled soils.” Untilled soils are cooler.

But, Forrestel said, these are not enough of a paradigm shift. She recommended trying to shift the growing window itself.

Whyte advocated for using smart sensors and AI-enabled data analysis tools, which he uses, saying that useful technology is rapidly evolving.

Sponsors for the day’s event included Lumo, which makes smart valves, and Meter.Me, which held demos in the morning. Each is used by winery clients in Napa.

“We can find those shallow root systems that stay green and transpire throughout the season,” said Whyte, thus cooling ground temps.

Coderey emphasized that more attention should be paid when planting and grafting vines to ensure the vine is not strangulated, impeding its uptake of water. In contrast to an AI approach, Coderey, who has worked in California for decades, including at Bonny Doon, Tablas Creek, Grgich Hills Estate, Preston and elsewhere, said he relies on “natural intelligence,” hoping to make growers more attentive and attuned to their vines.

“I see this as an industry that really wants to make a change,” Famiglietti said. “Everyone knows that it needs to make a change,” adding the interaction of scientists and growers and technologists was a positive step forward.