Comparative analysis of evaporation estimation formulas for long-term agricultural water resource management

Accurate evapotranspiration estimation is critical for optimizing water resource management, agricultural planning, hydrological modeling, and climate adaptation. This study evaluates the performance of two evapotranspiration estimation formulas: the Hargreaves (HG) formula and the Penman-Monteith FAO (PM FAO) formula, utilizing meteorological data from 2017 to 2020 collected at eight sites within the Nakdong River basin. The analysis demonstrates that the PM FAO formula exhibits a superior correlation with observed monthly and daily average evapotranspiration rates compared to the HG formula. The MAE of the HG potential evapotranspiration was 1.81 mm/day, with a tendency for overestimation, particularly in the summer. In contrast, the Mean absolute error (MAE) of the PM FAO potential evapotranspiration was 1.26 mm/day, showing less error than the HG formula. Performance indices, such as NSE and R², further supported the "Good" rating for PM FAO across most study areas. Although the PM FAO formula requires extensive data, it offers more accurate potential evapotranspiration estimates. Thus, integrating the PM FAO formula into models used for agricultural and water resource management, where data availability permits, can significantly improve flow estimation accuracy, supporting better-informed decision-making for sustainable water resource management.