Seasonal and annual variability of reference evapotranspiration at Rahuri in Semi-Arid Region of Western Maharashtra

Reference evapotranspiration (ET₀) serves as a critical indicator of atmospheric water demand and is essential for irrigation scheduling, crop water requirement estimation, and long-term water resource planning. This study investigates the temporal variability and trends of ET₀ at Rahuri, Maharashtra, a semi-arid region of Western India, using 50 years (1975-2024) of daily meteorological data. ET₀ was computed with the FAO Penman-Monteith method through the Phule Jal app, while statistical characteristics, linear trend analysis, and non-parametric Mann-Kendall (MK) test with Sen’s slope estimator were employed to evaluate trends at monthly, seasonal, and annual scales. Results revealed pronounced seasonal and monthly variations, with annual mean ET₀ estimated at 1683.41 mm. Summer exhibited the highest water demand (634.85 mm), while monsoon showed the lowest variability. May contributed the maximum share (14.36%) to annual ET₀, reflecting peak evaporative demand. Trend analysis indicated a highly significant long-term decline in ET₀ at annual, seasonal, and monthly scales, with Sen’s slope showing reductions of -12.37 mm/year (annual) and -6.96 mm/year (summer). The decline was most evident during March, April, and winter months, while some decades exhibited short-term reversals or non-significant changes, particularly in monsoon and post-monsoon periods. These findings highlight the evolving nature of atmospheric water demand in semi-arid regions and emphasize the need for adaptive irrigation and water management strategies under changing climate conditions.