Minutes from the Giesco
The XXIth giesco conference took place in Mendoza between November 6 and November 10th, 2017. The 4 days meeting gathered international scientists to discuss advances in the field of viticulture. We would like to share with our readers some of the topics discussed during the 2017 edition. Minutes from previous Giesco event are listed here. Today we summarize some of the talks focusing on climate change effects on wine grape production.
Rising temperatures in context
Annual temperatures are rising, globally. Depending upon the model used, an increase of + 1.6C up to +5 C is predicted by the end of 21st century. From a wine grape standpoint the temperature rise will globally hasten the timing of budbreak, bloom, veraison and full ripeness. On a berry chemical level, sugar concentration will increase earlier. Higher levels of sugars are expected to be reached before color reaches its maximal potential.
Effect on large region scale
In this context, Dr Villalba (Argentina) explained that more extreme climatic events should be expected. In Argentina that means, wetter summers but also drier winters. Overall, as glaciers are melting faster, Argentinean viticulture will face water reserve shortage in the long run. To anticipate the negative effect of climate on production, Dr. De Lorenzi (Italy)presented an approach to assess yield decline for different cultivars as temperature and evaporative demand increase while less water is available.
Effect on vineyard scale
We know at a large scale temperature will rise, but how will this affect phenology and the timing of plant development at the scale of a vineyard? and what will be such effects on wine properties such as alcohol and acidity? To address these questions, Dr. Le roux (France) presented a climatic approach which characterizes climatic trends at a fine scale. One of the challenge is that local climate variations are different from global climate changes. Local climate depends upon elevation, slope degree and slope aspect. Consequently, a new method accounting for vineyard local topography to predict changes in vineyard temperatures has been developed. Applied to St Emilion and Pomerol regions, it predicts the climatic trends between today and 2050 within a 25 m resolution. On average, results show an expected rise of 200 Growing Degrees days over the period April 1st –October for 2031-2050. In concrete terms, those predictions mean that new vineyard practices such as increased trunk height and late pruning will have to be considered for 2031-2050 in those Bordeaux regions. In the meanwhile, fine scale vineyard temperature maps can be used to select location for maturation sampling and tracking harvest date.
Lessons from the warm edge of warm viticulture
Dr. Kondouras (Greece) presented results from Greece, where some of the latest ripening varietals of the world have been planted to buffer the effects of high temperatures. But even Cabernet Sauvignon and the local Agiorgitiko, which are late ripening varietals, are showing an advancement in harvest date related to higher temperatures. Interestingly, another local varietal – Xinomavro- seems to be more resilient: so far harvest dates are unaffected by the impact of rising temperatures.
Understanding the effects of high temperature on earlier harvest dates for different varietals may benefit planting decisions. However, one should remain cautious: outside of hastening phenology, rising temperatures will also affect photosynthesis. This in turn could lead to unbalanced wines in terms of flavors and sugar /acid ratios.
The practical message I took home from those different studies is that winemakers may correlate earlier harvest dates with higher temperatures by looking at site specific data. For instance, the number of days when daily temperature is higher than 30C or the number of days when night time temperature is higher than 20 C should be relevant indexes to track.