California’s wine industry is a $6.5 billion market, and one that changes on a dime. In the past, the industry has been able to weather changing weather patterns by moving grapes around the state, but as temperatures rise in the state, the same resources are not being used to the same extent.

California accounts for about 30% of the U.S. wine industry, and is the largest grape-growing region in the world. It is also the most vulnerable to climate change, which is causing warmer temperatures and earlier growing seasons across the state. This year, two of California’s most famous wine regions—Sonoma and Napa Valley—have already begun to see the effects of climate change.

Most of us have heard the term “climatologist” at some point, but what does it really mean, and how does a climatologist work? In this episode, we talk to Jay Gulledge, a climatologist for the National Weather Service and a consultant to the California Department of Water Resources. Jay talks with us about what a climatologist is, what it takes to do the job, and the impact of climate change on the wine industry in California and around the world.. Read more about california wine climate change and let us know what you think.

The Winkler Index has been considered gospel by California winemakers for decades. The Index, which was created in the 1940s by two professors at the University of California at Davis (UC Davis), utilizes regional climatic variables to identify the optimum locations for growing a variety of wine grapes.

However, with the state under growing strain from heat and drought, the Index may be woefully out of date right now. U.C. Davis stated on July 22 that the Index will be updated for the first time in almost 75 years. This new fact has far-reaching consequences for the future of what we produce, create, and drink.

Professors A.J. Winkler and Maynard Amerine developed the Index to aid the recovery of the California wine business after Prohibition was repealed and vineyards were lost to phylloxera. The Index became a common method of deciding which wine varietals to grow there, and it was eventually adopted globally.

Stag's Leap vineyardStag’s Leap Wine Cellars/Leap Stag’s Wine Cellars/Leap Stag’s Wine Cellars/Leap Stag’s Wine Cellars/Leap Stag’s Wine Cell

The Index categorizes areas from I through V, with I being the coldest and V being the hottest. Between April and October, the normal growth season for grapes in the northern hemisphere, it monitors the quantity of heat from the sun through average daily temperatures over 50°F. “Degree days” is a term used to describe these heat units.

Region I is defined as places with less than 2,500 heat units in the initial ranking. This encompasses California’s Anderson Valley, Carneros, the Santa Cruz Mountains, and Santa Maria, as well as the Old World’s Mosel, Burgundy, and Champagne. These growing areas are most suited for Chardonnay, Pinot Noir, and Gewurztraminer, according to the Index.

Fresno and Merced, both in California, have 4,001 or more heat units, as do Algeria and Palermo, Italy, all in Europe. Grenache, Muscat Blanc, and Palomino wines that are sweet and/or fortified are suggested.

The Russian River Valley and Bordeaux (Region II) and St. Helena and Tuscany (Region III) lie in the middle, with heat units/degree days ranging from 2,501 to 3,500.

This new fact has far-reaching consequences for the future of what we produce, create, and drink.

The Napa Valley was mostly classified as a Region II and III when the Winkler Index was created, and was judged excellent for Cabernet Sauvignon. Today, Cabernet is planted on 50% of the land, or 22,868 acres.

Things, though, are changing. According to the 2018 Napa Vintage Report by Dr. Greg V. Jones, California has warmed an average of 2.3°F throughout the growing season between 1895 and 2018. Most of the valley now lies inside Regions III and IV, and others fear it may spread even farther.

Stag's Leap Cabernet SauvignonThe Fay Vineyard was one of the first in southern Napa Valley to be planted to Cabernet Sauvignon / Photo by M.J. Wickham

Warren Winiarski, 92, an environmentalist and renowned Napa Valley winemaker who created the winning Stag’s Leap Cabernet Sauvignon in the 1976 Judgment of Paris competition, is a proponent of revising the Winkler Index. He contributed $450,000 to U.C. Davis’ study in July.

“We need more sophisticated and comprehensive methods of assessing the impact of heat on plant physiology and grape maturity since we are in a time of climate change,” Winiarski adds. “The development of new measuring techniques would be very beneficial. We’ll be better able to react in the winery and produce the wines we want to make if we have a better understanding of changes in the compositional components in the grapes in the vineyard.”

Winiarski has seen both the 2017 and 2020 fires that ravaged the Napa Valley from the comfort of his house atop Stag’s Leap Wine Cellars. At his Arcadia Vineyard near Coombsville, he lost a barn and two homes, and he had to flee during the storm.

Warren Winiarski winkler indexWarren Winiarski contributed $450,000 to U.C. Davis research / Robert McClenahan photo

This season, data collecting for Napa Valley Cabernet Sauvignon has started. Plant development, berry chemistry, and other variables will be captured more efficiently than when the Winkler Index was developed, thanks to remote sensing and advanced monitoring technologies.

Growers and producers in the Napa Valley are anticipated to provide the U.C. Davis researchers some data from their own weather sensors.

The study is being led by Beth Forrestel, an assistant professor in the U.C. Davis Department of Viticulture and Enology. “There is a growing interest in understanding how to effectively minimize climate change impacts on current vineyards and select suitable cultivars for the future,” she adds. “The new techniques and data sources we’re introducing to this initiative will assist us in achieving that goal.”

Marcus Notaro, Winiarski’s successor at Stag’s Leap Wine Cellars, is among many who favor this update. He is in charge of the historic Fay Vineyard, which was one of the first vineyards in the Napa Valley’s southern stretches to be planted to Cabernet Sauvignon.

“Common belief was that our location in the Stags Leap District was too cold for Cabernet Sauvignon when Nathan Fay initially planted the vineyard in 1961,” Notaro adds. “Using current technologies to update this index will be a fantastic new tool to help our industry.”

It’s no secret that California’s wine industry is in crisis. The more than $10 billion industry has been battered by an array of factors, including drought, a changing climate and the decline of the American market. The state’s wine industry already faces a challenging future. A recent report from the University of California’s Center for Agroecology and Sustainable Food Systems found that only 1 percent of the state’s viticulture (the science and study of grape growing) is dedicated to climate change adaptation, the science of how to grow grapes in a changing climate.. Read more about future of napa valley and let us know what you think.

This article broadly covered the following related topics:

  • california wine climate change
  • climate change and wine
  • napa climate change
  • future of california wine
  • future of napa valley
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