Tjaša Pogačar

As spring frost proves to be an increasing risk throughout Slovenia and Europe, a better assessment of frost risk is needed. The statistical approach presented in this article consists of the conditional probability that the last spring frost occurs before budburst or flowering. The analysis was conducted using two separate phenological models and phenological data of various grapevine (Vitis vinifera L.), apple (Malus domestica), and sweet cherry (Prunus avium L.) varieties in locations across Slovenia. The increase in risk of spring frost for grapevine ranged from 1 to 1980, from 0.06 to 12 for apple, and from 1 to 180 for sweet cherry. Overall, the varieties most prone to frost proved to be Refošk (Teran) and Merlot grapevine varieties as well as the Germersdorf sweet cherry variety. We have identified the location in the hilly region with moderate climate where the Bobovec apple variety is grown as the least exposed to frost. Although counterintuitive, the GDD generally proved somewhat more efficient than the two-phase phenological model BRIN, although not in all cases. For the purpose of the study, the phenological models were calibrated, and the model parameters can serve as invaluable information for further research of this topic.