• Swetha Jayamurugan
• Aarthika Kudiyarasumani
• Manikumari Nagappan

This study evaluates four widely used empirical and theoretical formulae for estimating reference evapotranspiration (ETo): Hargreaves, Blaney-Criddle, Pan Evaporation and Penman-Monteith equations. These methods are assessed using meteorological data, including temperature, relative humidity, wind speed and solar radiation to determine their predictive accuracy and reliability. To compare their performance, statistical metrics such as Mean Absolute Error (MAE), Root Mean Squared Error (RMSE) and Coefficient of Determination (R² Score) are employed. MAE and RMSE measure the deviation between estimated and actual ETo values, while the R² score evaluates how well each model explains the variability in ETo. The results reveal that the Penman-Monteith equation consistently outperforms other methods, exhibiting the lowest RMSE and MAE values along with the highest R² score. Its superior accuracy is attributed to its comprehensive consideration of multiple meteorological parameters, particularly wind speed and radiation, which significantly influence evapotranspiration rates. In contrast, the Hargreaves and Blaney-Criddle equations, which rely primarily on temperature show higher errors due to their inability to account for the effects of humidity and wind. The Pan Evaporation method while moderately accurate, is dependent on local calibration and may not generalize well across different climatic conditions. These findings underscore the importance of selecting an appropriate ETo estimation method for irrigation planning and water resource management. The accuracy of the Penman-Monteith equation makes it the preferred choice for precise ETo estimation, particularly in regions with access to comprehensive meteorological data. However, in data-scarce areas simpler empirical models may still provide useful approximations with proper calibration. Future studies may focus on integrating machine learning techniques to enhance ETo prediction by combining empirical methods with data-driven approaches.

Reference evapotranspiration (ETo): Hargreaves, Blaney-Criddle, Pan Evaporation and Penman-Monteith equations

"Comparative Study of ETo Prediction Methods Using Empirical Formula", International Journal of Emerging Technologies and Innovative Research (www.jetir.org), ISSN:2349-5162, Vol.12, Issue 2, page no.f562-f567, February-2025, Available :http://www.jetir.org/papers/JETIR2502577.pdf

"Comparative Study of ETo Prediction Methods Using Empirical Formula", International Journal of Emerging Technologies and Innovative Research (www.jetir.org | UGC and issn Approved), ISSN:2349-5162, Vol.12, Issue 2, page no. ppf562-f567, February-2025, Available at : http://www.jetir.org/papers/JETIR2502577.pdf