Reference evapotranspiration trends and climate sensitivity in a semi-arid basin

This study examines the long-term trends and climatic sensitivity of reference evapotranspiration (ET0) in a representative semi-arid basin using 25 years of meteorological data. ET0 was calculated with the FAO-56 Penman‒Monteith method in CROPWAT 8.0. Temporal variations were analyzed using parametric methods, including linear regression and Pearson correlation, along with nonparametric techniques, such as the Mann‒Kendall test and Sen’s slope estimator. Multiple linear regression quantified climatic influences. The results revealed statistically significant upward trends in ET0 during most months, with the strongest increases occurring in mid-summer, while early spring exhibited no notable change. Annually, ET0 rose steadily with a Sen’s slope of approximately 0.05 mm/day per year. Strong agreement among the analytical methods confirmed the robustness of these results. Wind speed was identified as the most influential factor, accounting for over 90% of the relative contribution to ET0 variability in the sensitivity analysis (annual and summer). Overall, the results indicate rising atmospheric water demand under evolving climatic conditions, which amplifies drought risk, heat‑related crop stress, and agricultural vulnerability in this semi‑arid basin. These results provide a scientific basis for drought risk assessment and adaptive water management policies.