Adaptation to climate change by determining grapevine cultivar differences using temperature-based phenology models: This article is published in cooperation with the XIIIth International Terroir Congress November 17-18 2020, Adelaide, Australia. Guests editors: Cassandra Collins and Roberta De Bei

Grapevine phenology is advancing with increased temperatures associated with climate change. This may result in higher fruit sugar concentrations at harvest and/or earlier compressed harvests and changes in the synchrony of sugar with other fruit metabolites. One adaptation strategy that growers may use to maintain typicity of wine style is to change cultivars. This approach may enable fruit to develop under temperature conditions similar to those typically associated with that wine style. We demonstrate that Grapevine Flowering Veraison (GFV) and the Grapevine Sugar Ripeness (GSR) models can be implemented as a means of testing the suitability of alternative cultivars as an adaptation strategy to climate change.Previous viticulture temperature-based models were reviewed and compared with the GFV and GSR models. The results from the original GFV and GSR models were combined to evaluate the classification of the 20 most represented cultivars. The GFV and GSR models were tested for three new historic and contrasting datasets: 31 cultivars in the VitAdapt collection, Bordeaux; Chardonnay, Champagne; and Sauvignon blanc, Marlborough. Errors of predictions were less than a week for flowering and veraison, and within 7-10 days for the time to reach relevant target sugar concentrations for these datasets. Future GFV and GSR projections for Chardonnay resulted in an advance at a rate of one to two days per decade for flowering and veraison, and two to five days per decade for time to 170 g/L sugar concentration for RCP 4.5 and 8.5 respectively.Therefore, the GFV and GSR models are highly accurate and easy-to-use temperature-based phenological models for predicting flowering, veraison and time to target sugar concentrations when tested under new conditions. The models can be applied for characterising new cultivars, and assessing thermal time to flowering, veraison and different sugar targets. They can be used to assess cultivar performance in winegrowing areas worldwide under current or future climate conditions. The classifications therefore enable growers and researchers to compare the phenology of cultivars in a region today and to consider adaptation options: selecting later ripening cultivars or choosing alternative sites in the context of climate change.