Future change in viticulture phenological stages and early frost risk in Istria region, Croatia

Temperature and precipitation have a significant affect on the growth of vines and consequently viticulture is highly affected by climate change. Measurements indicate changes in the occurrence of phenological phases in the present climate and it is expected that this trend will continue in future.

Istria is one of the most prosperous wine regions in Croatia with more than 3000 ha of vineyards. It is well known for cultivating traditional (Malvazija istarska, Teran, Hrvatica…) and introduced varieties (Chardonnay, Merlot…). Because of that, it is important to determine sign and the robustness of future changes in phenological stages as well as possibility of spring frost occurrence.

For this study climate change effect on 21 grapevine varieties cultivated in Institute of Agriculture and Tourism in Poreč, Croatia were analyzed. Linear correlation between meteorological parameters and phenological stages of each variety and Growing degree day (GDD) thresholds required to begin a particular phenological stage is calculated and tested in present climate and used as a constant in future period.

For future changes, daily output of temperature (Tmin, Tmax and Tmean) and total daily precipitation from three CORDEX Regional Climate Models (RCMs) simulations (CLMcom-CCLM4-8-17, SMHI-RCA4, CNRM-ALADIN5.3) for Croatian domain, were used to determine changes in beginning of three key phenological stages (budburst, flowering and veraison) in 30-year periods (2011-2040, 2041-2070) compared to historical run (1971-2000).

Results show that, as the temperature rises phenological stages occur earlier (especially budburst and harvest). This affects all varieties equally. Earlier budburst leads to possibility of spring frost damage particularly in the inland of Istrian peninsula. Because of that, occurrence of frost was studied in present and in future climate. Day with frost is determined with the use of minimum daily temperature and dew point temperature (Td) calculated from Tmin and relative humidity at 7CET. Conditions for frost occurrence are suitable if Tmin < 3°C and Td < 0°C. Results show that frost will be one of the determinal factors for grapevine in future, as it is in present.