Effects of temperature rise on grapevine phenology (Vitis vinifera L.): Impacts on early flowering and harvest in the 2024 Growing Season

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Numerous studies have documented that climate change will considerably impact grapevine phenology. In the 2024 growing season, notable differences emerged from the previous five years, between 2019 and 2023. Rising temperatures at the beginning of the growth cycle of grapevines began the phenology phases earlier, leading to earlier bud burst and flowering for various grape varieties in many regions of Türkiye. This study examines variations in phenological phases across different years, using short-term climate data from a weather station in a cv. Sultan 7 (Vitis vinifera L.) vineyard in Yunusemre, Manisa, Türkiye. The objective of the study is to determine the impact of temperature fluctuations ranging from January to September on grapevine phenology intervals during critical stages: bud burst, full bloom, veraison, and maturity, specifically for between 2019 and 2024. Evaluations focused on critical factors, including growth cycle duration, days within specific temperature ranges, effective heat summation for the variety, and the Winkler Index values. The 2024 growing season recorded the highest temperatures in April and June, and bud burst occurred 5 days (2021) to 10 days (2019) earlier, while full bloom was determined for 16 days (2019 and 2022) to 27 days (2021) earlier than in previous years. The findings showed that years characterized by earlier flowering, 2024 (day of the year (DOY) 120) and 2022 (DOY 136), may be associated with earlier harvest. In addition, the Winkler Index recorded a highest of 2945.01 growing degree days (GDD) in 2024, with a specific effective heat summation value of 2,138.79 GDD for variety in a shorter timeframe. The findings suggest that although the intervals between veraison and harvest tend to remain almost similar each year, early flowering, the ripening period, and elevated temperatures before veraison in the same season can greatly contribute to prompting an earlier harvest.