Viticulture zoning based upon solar irradiation using remotely sensed solar radiation and terrain information : a case study of the appellation of origin Côtes-de-Bourg (Bordeaux, France) | Zonage viticole basé sur le rayonnement solaire incident issus de l'imagerie satellitale et le relief : exemple de l'appelation d'origine des Côtes-de-Bourg (Bordeaux, France)

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anglais. Solar radiation has a major impact on grapevine development and berry ripening. It has a large influence on photosynthetic activity, as well as on anthocyanin and aromatic compound synthesis in grape berries. Incoming and intercepted solar radiations are also key-variables in soil water balance, water fluxes and plant water stress. However, irradiation data is seldom available in weather station records. In this paper, the use of a digital elevation model coupled with remotely sensed solar radiation is investigated in order to characterize the agroclimatic potential of a viticultural production area. First solar radiation data retrieved from the Helioclim-1 database is used to estimate direct and diffuse solar radiation proportions. Then, using r.sun algorithm, 50 meters resolution daily maps of global irradiation are produced, based upon a Digital Elevation Model (DEM). This method was applied to the winegrowing area Côtes-de-Bourg, Bordeaux, France. This region exhibits moderated orography (mean slope = 3°, with a standard deviation of 2.4°). However, cumulated incoming solar radiation from veraison to berry maturity (SVM index) varied from -13% to +9% of the horizontal surface values. A zoning was realized based on SVM index values, dividing Côtes-de-Bourg area according to the SVM index (low, medium and high) of 2003 to 2005. This zoning was compared to Vitis vinifera cv Merlot berries characteristics of 6 sites located in areas of high and medium SVM index. Sites located in high SVM index area produced berries with lower titrable acidity, higher pH and higher mean weight than sites located in areas characterized by medium SVM index. No significant difference was found with berry sugar concentration. The solar radiation mapping methodology presented here is applicable for European and African vineyards, as satellite sensed solar irradiation data is compiled in the Helioclim-1 database, available at http://www.sodais.org.