Comparative Study of Temperature, Radiation and Mass Transfer based Models for Estimation of Reference Evapotranspiration in Iran's Northern Regions

Abstract

Evapotranspiration is the most crucial factor in hydrological and climatic research, as well as irrigation planning and management. A straightforward technique of estimating reference evapotranspiration (ET_o) is highly desirable, particularly in developing regions where the meteorological data needed for the conventional FAO Penman-Monteith (FAO-56) approach is either unavailable or insufficient. Thus, the purpose of this study is to assess and assess various ET_o estimate techniques against the FAO-56 approach and to identify the optimal ET_o estimation equation among straightforward experimental techniques as a viable substitute for the FAO-56 method. Data from Northern regions of Iran were used to assess the applied models. In this research, fifteen common methods of estimating ET_o including temperature, radiation, and mass transfer-based models were used in both their original and calibrated versions. Temporal and regional calibration procedures were also performed to assess the calibration effect on modeling performance improvement. ET_o calculated from equation of Hargreaves-Samani 4 (HS4) in based on temperature methods in Talesh station (SI=0.167, NS=0.927, CRM=0.002) and equation of Turc (TU) in based on radiation methods in Babolsar station (SI=0.124, NS=0.963, CRM=0.052) and equation of Meyer (ME) in based on mass transfer methods in Ramsar station (SI=0.316, NS=0.738, CRM=0.001) with the lowest error percentage of each group showed the best estimate compared to the FAO-56 method. These findings highlight the adaptability and accuracy of HS4, Turc, and Meyer, recommending them as practical alternatives to the FAO-56 method, particularly in data-scarce regions.