Climate change impact study based on grapevine phenology modelling

In this work we present a joint model of calculation the budbreak and full bloom starting dates which considers the heat sums and allows reliable estimations for five white wine grape varieties (Chardonnay, Szürkebarát (Pinot gris), Pinot blanc, Riesling, Hárslevelű) and their clone varieties in Hungary (Chardonnay 75 and 96, Riesling 239, 378, 391 and 49, Hárslevelű P.41 and K.9., Pinot blanc 54, 55 and D55, Szürkebarát 34 and 52). The base lower and upper temperatures have been determined by optimization, above which (threshold temperature) the accumulation of daily means is most active, or alternatively, below which the daily means are most sensitively expressed in the phenology. The model has been extended to the calculation of the end of the rest period (endodormancy), by optimization as well. We determined the lower and upper base temperatures separately for the budbreak and full bloom starting dates such that the lowest (normalized) sum of squares error, the lowest average absolute and the lowest maximum error of predictions can be achieved. We determined the optimal (lower) base temperature as 6 °C and the optimal starting date as the 41st Julian day of the year for the budbreak. Moreover, we set 10,45 °C and 26 °C as lower and upper optimal base temperatures for full bloom. The joint model was then applied to study the impact of climate change on budbreak and full bloom starting dates based on RegCM3.1 (regional) climate model. We calculated the expected shifts of budbreak and full bloom and proved that the changes are significant.