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Warming Threatens Future of Premium Napa County Wine Grapes: Research

A new study indicates that Napa County could suffer a loss of 50-70% in available acreage for growing of high-quality wine grapes by 2039. This decrease would be due primarily to an increase in the number of excessively hot days in the effected areas. The study was a collaborative effort led by Noah S. Diffenbaugh of Stanford University. It was published on June 30, 2011 in Environmental Research Letters.


The intent of the research was not to cause a panic or sudden rush to sell vineyard land. The goal was to generate projections of climate change impact on premium grape growing. That can be used in designing ways to adapt to the increased heat, thus reducing its impact. The researchers applied their projections to four premium wine growing regions: Napa County, Santa Barbara County, Walla Walla County (Washington) and Yamhill County (Oregon).

The most severe impact of global warming was seen on the growing regions of Napa County. That region, among those studied, already has the highest mean growing season temperature. Further increases in temperature due to global warming were projected to push much of Napa beyond the threshold appropriate for high-quality grapes. This is based both on 20 degrees Celsius being the maximum acceptable temperature for high-quality grape growing on any given day and A. Winkler’s Growing Degree Days (GDD) summation. On the Winkler scale, Napa County is currently categorized as a Region III (1671 to 1950 GDD), suitable for volume production of good wine. The study shows much of Napa Country transitioning to Region IV (1951 to 2220 GDD). That is also good for production levels, but wine quality decreases to acceptable or worse. The study only examined the impact of temperature on change on vines and grapes. It did not examine how temperature increases might impact water supply, weather patterns, etc.

More bad news is that it doesn’t take much warming to cause harm. An average increase of just a single degree Celsius would cause the substantial losses mentioned above, according to the stduy. However, as the researchers point out, that means finding ways to adapt to that one degree increase — essentially raise the maximum acceptable temperature from 20 to 21 or 22 degree Celsius — could eliminate all of those losses. Clearly, quickly finding effective means of adapting to higher temperature is critical.

The complete study is here: Climate adaptation wedges: a case study of premium wine in the western United States (it’s very technical, but not very long).

For more about growing degree days: Winkler A et al 1974 General Viticulture 4th edn (Berkeley, CA: University of California Press)

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This article is original to Copyright 2011 NorCal Wine. Global Warming graphic by created by MikeEdwards. All rights reserved. Temperature change banner courtesy of NASA.