Repercussions del canvi climàtic en la qualitat del vi de garnatxa negra en les terres de Tarragona i el Priorat

Abstract

The rising temperatures and reduced rainfall in the new scenario of climate change are causing a loss of both yield and quality in viticulture. Catalan Grenache is a variety that is very well adapted to drought in the Mediterranean area but despite this, grape and wine composition may be affected under severe weather conditions. The negative effects of high temperature should be noted since it diminishes the synthesis of phenolic compounds, a factor which is directly related to the quality of red wines. To assess the oenological aptitudes of Grenache and to evaluate the effect of the terroir and climate variability, the yield and phenolic composition of Grenache grapes in different plots of the Tarragona and Priorat areas were compared for two vintages. The initial objective (study A) was to determine the effect of climate change at vineyards of variable topography in the DOQ Priorat on the yield and composition of Grenache grapes in two vintages of opposite climatic situations (temperate versus extremely hot in the year 2002 and 2003 vintages). A second study (study B) evaluated the effect of climate change during two hot vintages (2011 and 2012) in two different terroirs: DOQ Priorat and DO Tarragona. Phenolic maturity was determined together with a measurement of the water potential and wine composition. The ANOVA statistical analysis of variance and the Tukey test were applied to the results of each plot in the study. Study A observed that in hot years anthocyanins decreased in early regions; by contrast, in temperate years, anthocyanins reached similar concentrations except for the grapevines growing at higher altitudes, where the grapes did not reach complete ripeness. In early areas alone, there was a significant decrease in anthocyanins one week before harvest. Topography was the variable with the most influence on the yield; upper terraces provided smaller harvests. The rising temperatures between veraison and maturation affected the composition of the pulp, causing a disjunction between pulp ripeness and phenolic content in the skin. Study B observed that the lowest water potentials were recorded in the DO Tarragona (T), where the plants have a larger reserve of soil water and transpiration is higher. The berry size was smaller in 2012, when temperatures increased significantly at the end of ripening. Sugars reached the highest concentrations in the DOQ Priorat (P). Priorat wines showed a higher phenolic content index (TPI), but in the DO Tarragona there was a higher concentration of tannins. The yield decreased markedly in dry years in the DOQ Priorat alone.