Zone-Wise Estimation and Spatio-temporal Variability of Potential Evapotranspiration in Maharashtra Using the Thornthwaite Method

Potential evapotranspiration (PET) is a fundamental parameter of the hydrological cycle, reflecting atmospheric water demand and serving as a critical input for irrigation planning, drought assessment, and climate change impact studies. This study evaluates the zone-wise estimation and spatial variability of PET across nine agro-climatic zones of Maharashtra, India, over the period 1991–2020, using the Thornthwaite method. Long-term daily temperature data were utilized to calculate PET, and annual and inter-annual variations were assessed to capture spatial heterogeneity and temporal dynamics. Results indicate substantial spatial variability, with mean daily PET ranging from 3.75 mm day⁻¹ in the Western Maharashtra Plain to 5.70 mm day⁻¹ in Central Vidarbha, highlighting higher atmospheric water demand in semi-arid inland regions and lower demand in the Western Ghats and Konkan coastal areas. Temporal analysis revealed moderate inter-annual fluctuations, with PET peaks corresponding to drought-prone and high-temperature years, reflecting sensitivity to regional climatic variability. These findings are consistent with observed patterns in semi-arid and humid regions reported in prior studies. The study demonstrates the suitability of the Thornthwaite method for long-term, large-scale PET estimation in data-scarce regions and provides zone-specific insights for targeted irrigation scheduling, water resource management, and climate-resilient agricultural planning in Maharashtra.