Projected Variations in Reference Crop Evapotranspiration Across Türkiye

Climate change is expected to intensify evapotranspiration dynamics globally, posing significant challenges for sustainable water management and agricultural productivity. This study assessed the spatial and temporal variability of reference crop evapotranspiration (ETo) across Türkiye using the HADGEM climate model under RCP4.5 and RCP8.5 scenarios for the near (2023-2052) and far future (2069-2098) periods, relative to the reference baseline (1971-2000). ETo was estimated using the FAO Penman Monteith equation by ETo Calculator, while temporal persistence and variability were examined through the Spearman rank correlation and coefficient of variation, respectively. Results revealed a widespread and statistically significant increase in ETo across most regions, with the most pronounced changes occurring under the far-future RCP8.5 scenario. Average ETo increases exceeded 25% in continental and southern provinces such as Isparta, Niğde, and Gaziantep, while the humid Black Sea region remained the least affected, showing increases below 20%. Seasonal analyses identified summer as the most stable yet intense evaporative period, and winter as the season with the highest variability. These findings indicate that rising temperatures and altered humidity-radiation interactions will substantially increase evaporative demand and irrigation requirements. Consequently, region-specific adaptation strategies and integrated water management policies will be critical to ensure agricultural resilience under future climate conditions.