Estimating spatial and temporal variations in solar radiation within Bordeaux winegrowing region using remotely sensed data

Aims: This paper presents a study of spatial and temporal variations in solar radiation for the Bordeaux winegrowing region, over a 20 year period (1986-2005). Methods and results: Solar radiation data was retrieved from the HelioClim-1 database, elaborated from Meteosat satellite images, using the Heliosat-2 algorithm. Daily data was interpolated using ordinary kriging to produce horizontal solar radiation maps at a 500 m resolution. Then using a digital elevation model, 50 m resolution daily solar radiation maps with terrain integration were produced for the period 2001-2005. The long term (20 year) analysis of solar radiation at low spatial resolution (500 m) showed a west to east decreasing gradient within the Bordeaux winegrowing region. Mean August-to-September daily irradiation values, on horizontal surface, were used to classify the Bordeaux winegrowing region into three zones: low, medium, and high solar radiation areas. This initial zoning was downscaled to 50 m resolution, applying a local correction ratio, based on 2001-2005 solar radiation from the inclined surface analysis. Grapevine development and maturation potential of the different zones of appellation of origin of Bordeaux winegrowing regions are discussed in relation with this zoning. Conclusion: Solar radiation variability within the Bordeaux winegrowing region is mainly governed by terrain slopes and orientations, which induce considerable variations within the eastern part of Bordeaux vineyards. Significance and impact of study: Solar radiation has a major impact on vineyard water balance, grapevine development and berry ripening. However, irradiation data is seldom available in weather stations records. This paper highlights the need for high resolution mapping of solar radiation that uses remote sensing and terrain effect integration for agroclimatic studies in viticulture.