Risk assessment of frost occurrence in a changing climate

Frost events that occur after the beginning of the growing season pose great risk for fruit trees, especially after budburst. There have been attempts to model frost risk projections for the 21th century in Slovenia, however the results have shown no change in frost risk due to climate change, despite observations for years 2019 and 2020 showing otherwise. Therefore, an alternative climatological analysis of frost event probability is of great importance, especially in combination with phenological data from Slovenian fruit tree orchards and vineyards. An assessment of the risk of tardive frosts for a series of Slovenian fruit tree orchards and vineyards throughout the 21st century was made from temperature data of climate model projections, specifically from regionally downscaled projections data. The analysis bases on two pheonological models for calculation of budburst - a classic GDD model and a two-phased BRIN model. Afterwards the approach consists of a comparison of the statistical probability of two events, the last frost event probability (day of the year) and a budburst event probability, as simulated by the different phenological models. We discovered that the probability of a tardive frost, i.e. frost events occurring after grapevine budburst, in Slovenian grapevine varieties varies throughout the 20^th and 21^th century, for example, the probability of a tardive frost increases towards the end of the 21^th century for Chardonnay (Eastern Slovenia with continental climate) and Riesling (Northeastern Slovenia with continental climate) varieties but decreases for Merlot (Southwestern Slovenia with Mediterranean climate). An analysis of tardive frost projections for cherry, apple, olive and other fruit tree varieties grown in Slovenia is under way. Some preliminary results of the project will be represented.