Since 1950, extreme hot temperatures (hot days, tropical nights and heat waves) have become more frequent (IPCC, 2014).
Since 1880, the mean duration of summer heat waves in Western Europe has doubled, and the frequency of hot days has tripled. Since 1960, the number of hot days (those over the 90 percentile of a reference period) has almost doubled all over Europe (EEA, 2016).
An earlier flowering and ripening of the grapes have been observed worldwide. Apart from the impacts on yields, a negative effect on the wine quality is also expected in some regions and grape varieties, resulting from altering the share of sugars and acids (IPCC, 2014).
These changes in the phenology entail that the ripening of bunches occurs under higher temperatures, affecting the composition of grapes (Schultz y Jones, 2010). This fact, together with the purpose of many wineries to achieve more structural and potent wines (with a better score by reviewers in the different classification systems), has made the ripening process to lengthen too much, with the intention of achieving a complete phenolic maturity (Jones y Webb, 2010). As a result, grapes with a higher alcohol content and high pH are obtained. In fact, producers and consumers have already experienced changes in some wines regarding their alcohol content.
Likewise, another interesting indicator is the Cool Night Index (based on the minimum temperatures in September), which determines the color and aroma of grapes. These are distorted in warmer scenarios (Tonnieto and Carbonneau, 2004).
Source: Baseline Report AgriAdapt and Cayo Isidro Armas Lima (La Rioja University)