Solar radiation in the Uruguayan coast of the Río de la Plata and its relation to viticulture climate indices

Abstract

The magnitude and distribution of solar radiation have an important impact in yield and vintage composition. In this study we analyzed solar radiation levels in the uruguayan coast of the Río de la Plata in relation with the viticultural climate indices. Its relationship with other meteorological variables was also investigated. The hourly solar irradiation at ground surface was obtained using a satellite-based model for six vineyards’ locations.  The model is a modification of  a pre-existing statistical model (Justus et al., 1986) that was especially adapted for Uruguay’s territory and surrounding areas using quality controlled radiation measurements (Alonso Suárez et al.,2012). Solar radiation data were generated for the four vintages (2011 to 2014) that were studied. The viticultural climate indices were calculated according to the Geoviticulture MCC System, adapted to Uruguayan conditions. Results show a decreasing trend of solar radiation in the West-East direction. This trend was more pronounced during the summer season. The accumulated values of solar radiation during the growing cycle showed high correlation (Pearson’s coefficients) with the following variables: Penman’s potential evapotranspiration(r=0,90), heliophany (r=0,84), maximum air temperature(r=0,69),mean air temperature (r=0,62), accumulated rainfall (r=-0,83), relative air humidity(r= -0.63), Heliothermal index (HI), r=0,74) and Growing Degree Days (GDD10) (r=0,65 ). The Dryness index (SI) showed high correlation with irradiation in February (r = -0,64), while no correlation with the Cool Night index (FI) was observed. All correlation coefficients were highly significant, with p-values lesser than 0.0001. The determination of regional “profiles” of solar radiation can be used as a tool to delimit viticultural site, adjust cultural practices and characterize vintages.