Spatial analysis of climate in winegrape-growing regions in Australia.

Background and Aims:  Temperature-based indices are commonly used to indicate long-term suitability of climate for commercially viable winegrape production of different grapevine cultivars, but their calculation has been inconsistent and often inconsiderate of within-region spatial variability. This paper (i) investigates and quantifies differences between four such indices; and (ii) quantifies the within-region spatial variability for each Australian wine region. Methods and Results:  Four commonly used indices describing winegrape growing suitability were calculated for each Australian geographic indication (GI) using temperature data from 1971 to 2000. Within-region spatial variability was determined for each index using a geographic information system. The sets of indices were compared with each other using first- and second-order polynomial regression. Heat-sum temperature indices were strongly related to the simple measure of mean growing season temperature, but variation resulted in some differences between indices. Conclusion:  Temperature regime differences between the same region pairs varied depending upon which index was employed. Spatial variability of the climate indices within some regions led to significant overlap with other regions; knowledge of the climate distribution provides a better understanding of the range of cultivar suitability within each region. Significance of the Study:  Within-region spatial variability and the use of different indices over inconsistent time periods to describe temperature regimes have, before now, made comparisons of climates between viticulture regions difficult. Consistent calculations of indices, and quantification of spatial variability, enabled comparisons of Australian GIs to be made both within Australia and with American Viticultural Areas in the western United States.