Climate variability: influence on grape composition and yield

Abstract

Within consideration of climate change, it is essential to understand the influence of year to year climate variability and its impact on quantity and composition of grapes, in order to take appropriate decisions for a sustainable viticulture. Climate variability at a regional scale was analyzed for the period 1972 -2014, while its influence on grape yield and composition was studied during the period 1993 – 2014. Measurements were made on 30 plants selected at random in a Tannat vineyard trained on a VSP trellis system. Grape yield, weight, sugar contents (refractometry) and total acidity (titration). Climate information was obtained from a weather station (OMM regulation) located at a distance of 5 km from the vineyard and calculated the Huglin Heliothermic index, Cold Night index, temperature and rainfall. Multivariate analysis (Principal Component Analysis PCA and Hierarchical Ascendant Classification HAC) was performed using the statistical package InfoStat. Similarity between groups was estimated following PCA results. Climate variables of the series 1972 – 2014 indicate recurrence, showing variability in time in response, most of the years, to the “El Niño/Niña” – Southern oscillation (ENSO). Within the 1993 – 2014 cycle, the PCA identifies groups of wine years, as either predominantly warm or mostly rainy. The both two first components explained 54.2% of total variance, considering the climate, yield and grape composition variables. The HAC classified the years, according to the effect “El Niño/Niña” o Neutral. Thermal climate variables correlated positively with yield and negatively with grape composition. The hydric variable correlated positively with acidity. In order to make the analysis two separate groups of years were considered, according to average sugar concentration and yield values. Years with above average values of sugar concentration and below average in yield showed a 50% correspond with “Niña – years” and 37,5% correspond with “Neutral-years. El Niño showed a below average sugar contents in 6 of the 7 years considered and above average yield. Climate variable values, modified by the ENSO cycles are, very likely, good predictors for grape composition and yield.