Climate Influences on Grapevine Phenology, Grape Composition, and Wine Production and Quality for Bordeaux, France

A long-term (1952-1997) climatology was developed using reference vineyard observations in Bordeaux, France. The procedure partitioned the season into growth intervals from one phenological event to the next (budburst, floraison, veraison, and harvest) in which climatic influences were summed and assessed. The data were then used to investigate the relationships between climate and phenology, berry composition at harvest, total production, and quality. Over the last two decades, the phenology of grapevines in Bordeaux has tended towards earlier phenological events, a shortening of phenological intervals, and a lengthening of the growing season. Merlot and Cabernet Sauvignon varieties have tended to produce higher sugar to total acid ratios, greater berry weights, and greater potential wine quality. Vintage ratings have shown a general increase over the last two decades paralleling the observed phenology and composition trends. The composition and quality trends were mostly described by increases in the number of warm days during floraison and veraison and a reduction in precipitation during maturation. Production variability was not as readily described by phenological-interval climate parameters, but regression modeling did indicate that rainfall during physiologically important periods (flowering and maturation) tended to decrease crop production. By variety, the relationships between phenology, climate, and composition were typically higher (both positive and negative) for Merlot than for Cabernet Sauvignon and could be an indication that, in Bordeaux, Merlot is more phenologically and climatologically sensitive. Additionally, sugar to acid ratios revealed that both Merlot and Cabernet Sauvignon composition influenced Bordeaux wine quality, although variations in Cabernet Sauvignon described substantially more of the variability in ratings. This indicates that the wine industry in Bordeaux is more dependent Cabernet Sauvignon for good vintages than on Merlot.