• Dona Stewart

France's Vineyards Heat Up - Again

An Unprecedented Second Heat Wave

Only a month ago, France endured unseasonable, record-breaking high temperatures. The earliest heatwave since 1947 brought average daily temperatures above 40ºC (104ºF). This followed the hottest May on record and hailstorms in early June.

During the mid-June heatwave, or canicule, 18 million people were under an alert. For only the fourth time, the government issued the ‘red alert’, indicating an extreme, long duration event. The alert impacted 12 departments, mostly in the south and southwest France. In Bordeaux, temperatures of 40.2ºC (104.5ºF) prompted the cancellation of the Sauternes Fête le vin.

Another heat wave has arrived, as of today, 23 departments are under a yellow alert. This wave, caused by a ‘heat plume’ may be of even longer duration. Select forecast temperatures in Paris and key wine regions for Monday, July 18:

Paris 38.9ºC/102ºF

Épernay 38.3ºC/101ºF Beaune 37.2ºC/99ºF Bordeaux 38.9ºC/102ºF

Sancerre 33.9ºC/93ºF

Avignon 38.9ºC/102ºF

Impact on the Vineyard

It is difficult to predict the precise impact this will have in the vineyard; France has never before experienced such ‘back-to-back’ heatwaves, nor such extreme heat this early in the year. Conditions have also been extremely dry. This past weekend a large wildfire burned over 880 hectares (2,100 acres) in the Gard region in the southeast, prompting evacuations.

Research from California’s San Joaquin Valley, where extreme heat events have been more common for years, found that sunburn and severe water stress cause “significant yield loss and poor berry quality at harvest.” Photosynthesis decreases when the canopy temperature exceeds 30°C and vines begin to ‘shut down’. High temperatures in the grape itself can accelerate the breakdown of acids, essential for retaining freshness in the final wine, and degrade the organic compounds that provide color and flavors.

The long duration of this heatwave may cause greater losses. Computer models of the impact of heatwaves on European winemaking regions using high-resolution weather, soil and terrain datasets from 1986 to 2015, estimated yield loss by geography and duration of the heat event. In France, the research team predicted the Loire Valley, Alsace and Bordeaux would be the most impacted regions. Following nine days of heatwaves, yields would decrease by 30-35%, but only 20% following five days of extreme heat.

For the vignerons, who faced a difficult 2021 marked by frost and cold, the next week will be pivotal for determining the size and character of the 2022 harvest.

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