干旱区生态环境知识资源中心

Accurate estimation of reference evapotranspiration (ETo) is essential for water resources management and irrigation systems scheduling, especially in arid and semiarid regions such as Iran. In the present research, constant coefficients of Hargreaves-Samani (CH-S) and Priestley-Taylor (CP-T) equations were locally calibrated to estimate the ETo based on the FAO-Penmen-Monteith (PM) method as standard method. For this purpose, meteorological data of eight synoptic stations located in the northwest of Iran were used during the period of 1997-2008. The outcomes showed that the values of CH-S and CP-T were 0.0026 (instead of 0.0023) and 1.68 (instead of 1.26), respectively. Also, at stations with high wind speed, the values of calibrated coefficients of CH-S and CP-T were maximum. Then, the estimated ETo values using adjusted CH-S and CP-T coefficients were compared to the obtained actual ETo values by PM method using root mean square error and mean bias error indices. The results indicated that the new calibrated H-S and P-T equations have good agreement with the PM method for estimation of the ETo. Moreover, the equation of Ravazzani et al. was calibrated in the studied region. It was concluded that in general, the mentioned equation was shown better performance than original H-S equation.