Monitoring viticultural response to hydrological stressors (2017-2025) in three sites in Peloponnese
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Date
2026-02-06
Authors
Μπακάλη, Ιωάννα
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Abstract
The Mediterranean region, recognized as a climate change hotspot, is experiencing increased frequency and intensity of extreme hydrometeorological events, including heatwaves and droughts. Viticulture, a cornerstone of Mediterranean agriculture, and a major economic sector in the Peloponnese, is particularly vulnerable to these compounding stressors. This study investigates vineyard vegetation response to heatwaves and drought events across the Peloponnese region during 2017-2025, utilizing multi-scale remote sensing data and climate indices. High-resolution drone imagery (3 cm per pixel) was collected over vineyards in Pyrgaki Aigialeia, Pyrgaki Messenia, and Romanos Messenia and upscaled to Sentinel-2 spatial resolution (10 m × 10 m), integrating UAV observations with satellite monitoring, to evaluate cost-effective, long-term viticulture monitoring approaches. Normalized Difference Vegetation Index (NDVI) time series from Sentinel-2 during the growing season (June-September) characterized vegetation dynamics throughout the study period. Meteorological data from ERA5 reanalysis were used to identify heat wave events and calculate the Standardized Precipitation Evapotranspiration Index (SPEI-1) as a drought indicator. In situ data were used to evaluate satellite measurements. Heatwaves were defined as periods of at least three consecutive days with maximum temperatures exceeding the 95th percentile of the 1961-1990 reference period, enabling better assessment of climate change impacts. Drought conditions were identified when SPEI-1 values (also referenced to 1961-1990) fell below -1.0. The year 2018, characterized by wet conditions and absence of heatwave events, served as a control year for comparison. Cross correlation analysis quantified temporal relationships and causality between heat waves and NDVI, as well as between SPEI-1 and NDVI, as well as between SPEI-1 and NDVI, revealing vegetation lag-response to hydrometeorological stressors. NDVI reached minimum values 15 ± 2 days after heatwave onset across all sites. Previous year July SPEI-1 correlated strongly with subsequent June NDVI (r = +0.84 to +0.92, p < 0.01), with heatwave duration showing even stronger predictive power (r = -0.89 to -0.95, p < 0.01), explaining up to 90% of inter-annual variance. Additionally, July emerged as the critical control month, with previous year's July climate conditions explaining 85-90% of next season's vegetation health. Compound drought-heatwave events during this critical véraison period depleted carbohydrate reserves, eliminating the vine's capacity for interseasonal recovery. A critical transition occurred in 2021 that fundamentally altered both the climate forcing regime and vineyard response dynamics. Before 2021, vineyards exhibited temporary stress responses with full NDVI recovery between growing seasons, while heatwaves were less common and intense. The 2021 extreme summer marked a regime shift characterized by more frequent and severe heatwave events and alternating drought conditions. After this transition, all vineyards showed persistent vegetation decline (20-45% NDVI reduction) without seasonal recovery, indicating loss of normal biological cycles and sustained physiological damage through 2025. Especially, Romanos site experienced the most severe decline (~45%), while Pyrgaki Messenia site provided only partial buffering (~25% decline). This research demonstrates effective integration of drone-based and satellite remote sensing for viticulture monitoring and provides insights into vineyard resilience to climate extremes, with implications for adaptive management in Mediterranean agriculture.
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Keywords
Viticulture, Heatwaves, SPEI-1, Cross-correlation, NDVI, Sentinel-2, Drought, Mediterranean climate