Assessing the Interplay Between Climatic Conditions and Olive Phenology Using the Growing Degree Day Model

ABSTRACT Rising temperatures, shifting precipitation patterns, and increasing frequency of extreme weather events across the Mediterranean, driven by climate change, present significant challenges for olive cultivation, particularly if traditional soil management practices are not adapted. Croatia, located at the northern edge of the Mediterranean olive‐growing zone, represents the northernmost region where olives are cultivated. However, comprehensive agroclimatic studies in Istria (Croatia), especially those examining recent trends in olive tree phenology, remain scarce, providing the main motivation for this research. Our results indicate that rising minimum and maximum temperatures across Istria, particularly in spring, have increased growing degree day (GDD) accumulation during the growing season. This has advanced the onset of key phenological stages and shortened the overall growth period, with the Istarska Bjelica cultivar showing the most pronounced response. To further explore this, a simple GDD model was developed and tested as a prognostic tool for predicting the initiation of phenological stages. The model successfully captured the entire flowering period, performing best with a base temperature of 6°C. This highlights its strong potential for projecting the onset of olive flowering under future climate conditions and supporting more effective management decisions.