Micro-climate variations related to vineyard crop quality

The influences of daily weather extremes such as maximum-minimum temperatures, humidity and precipitation are observed in relation to grapevine phenology. The quality of a vintage is produced when the skill of the winemaker is combined with crop quality factors such as grape berry component ratios for sugar, aroma, flavour and colour pro-phenols. With reference to previous published work in climate influences on crop yield and quality, this paper describes a data mining approach used for data association modelling to depict dependency relationships between daily weather extremes, grapevine phenology, crop yield and wine quality indicators. This method is applied to sample data from a vineyard in northern New Zealand. The sample data was classified into two sub-sets reflecting high and low years. The classification parameters for membership of either set were defined in a min-max spectrum for crop yield (grapes harvested in tons/hectare) with values for a 12 year period. Climate data with values for daily weather extremes logged at a nearby meteorology station was pre-processed into a matrix of occurrence frequencies at continuous 3°C intervals within the lowest and highest of maximum temperature recorded in a moving three week window for 45 weeks prior to every harvest date during the 12 year period (1997-2009). The processed weather occurrence frequency and wine quality data sets were analysed for quantifying any new and already known associations between the two major sets of variables. An artificial neural network algorithm was used to classify the data associations and a chi-square statistical test was used to establish the degree of independence between the related variable values. Focussing on temperature variation for this study, the results show that temperatures <;23°C in mid Novemberearly December and >26°C in late February-March led to low yield years while conversely 23-26°C (so slightly cooler) and <;23°C (so slightly warmer) in the respective time periods led to high years in this particular vineyard. This is practically an inverse ratio where apparently minor temperature variations are significant.