Performance Evaluation of Empirical Reference Evapo-transpiration and Trend Analysis

Reference evapotranspiration (ETo) is a key component in agricultural water management and irrigation planning, as it represents atmospheric water demand under standard conditions.Accurate estimation of ETo is essential, especially in regions where direct measurements are limited.This study evaluates the performance of several empirical and semi-empirical ETo estimation methods against the FAO-56 Penman-Monteith (PM) method for the Gandhi Krishi Vignana Kendra (GKVK), Bengaluru, India.Daily meteorological data, including temperature, relative humidity, sunshine hours, and wind speed, collected over a 24-year period (2001-2024), were used for analysis.Multiple temperature-based and radiation-based ETo models were assessed using statistical performance indicators such as MAE, RMSE, MBE, R², NSE, and PBIAS.Results indicated large variability in model performance, with several temperature-based methods showing significant overestimation, while radiation-based models demonstrated comparatively better agreement with the FAO-56 PM estimates.Among all models, the Irmak-Allen and Priestley-Taylor methods showed the closest correspondence with the reference method.Seasonal trend analysis using the Mann-Kendall test revealed a significant increasing trend in winter ETo and a strong decreasing trend during the monsoon season, while pre-monsoon and post-monsoon trends were statistically insignificant.The findings highlight the importance of local calibration and seasonal analysis for improving the reliability of ETo estimation in sub-humid climatic regions.