Atmospheric circulation variability and vintage Port wine

The success of viticulture is inexorably tied to atmospheric conditions during the growing season. Previous work has tied observed and general circulation model (GCM)-projected changes in atmospheric variables to wine production in Europe. This research uses a synoptic climatological approach to examine the role of atmospheric circulation variability on wine production in the Douro Valley region of Portugal. Of particular interest is the atmospheric contribution to 'vintage Port' production. Vintage Port years are declared periodically and coincide with particularly high quality grape harvests. Results suggest that temperatures and potential evapotranspiration (PET) have increased significantly overall for the region, with the signal being present in both non-vintage and vintage years, while precipitation has remained statistically constant over the study period. Circulation analysis indicates that early winter ridging and drying offset by late winter pressure decreases and frontal cyclone tracking over the region is important during vintage years. Additionally, the analysis suggests that March synoptic drying followed by a significantly reduced PET during summer is important in vintage years. When followed by autumn maximum air temperatures and evapotranspiration rates that are significantly higher than normal, vintage Port results. Such conditions favor summer water retention in grapes, which increases the concentration of sugars through drying immediately prior to harvest. These results may be useful in alerting producers about quality of the upcoming harvest, especially as long-lead climate outlooks continue to improve.