Assessment of Reference Evapotranspiration: A Case Study Using Hargreaves and Penman- Monteith

This research paper presents a comparative analysis of reference evapotranspiration (ET0) estimation using the Hargreaves and Penman-Monteith equations for Annamalai Nagar, a region characterized by a humid climate. Accurate estimation of ET0 is vital for effective water resource management and agricultural planning. The study highlights the limitations of the Hargreaves equation, which relies solely on temperature and extraterrestrial radiation, resulting in an overestimation of ET0 at 12.08 mm/day. In contrast, the Penman-Monteith equation, incorporating temperature, wind speed, relative humidity, and net radiation, estimated ET0 at 4.7 mm/day. The substantial difference arises from the Hargreaves model's insensitivity to humidity and wind, making it less suitable for humid regions. The Penman-Monteith method, recommended by FAO-56, provides a more comprehensive and accurate approach to ET0 estimation. This study emphasizes the importance of selecting appropriate models based on local climatic conditions and suggests further research on integrating real-time meteorological data and machine learning techniques to enhance ET0 predictions.