Potential Evapotranspiration Model for Muda Irrigation Project, Malaysia

Abstract

Methods to estimate free-surface evaporation Ep and potential evapotranspiration ETp using well known models, namely, Penman–Monteith model, modified Penman method, Food and Agriculture Organization Penman–Monteith (FAO-PM) method, Blaney–Criddle method, and Christiansen method, without calibrating any model calibration parameters, for monthly time series are presented. The long-term monthly averaged daily models results are calculated using recorded average historic meteorological data (1980–1997) and compared with the USBR Class-A black pan evaporation data obtained from the Muda Agricultural Development Authority, Malaysia. The comparison results of the long-term monthly averaged daily estimates of Ep using these models show that the Ep values for the Penman–Monteith model and FAO-PM method for different months are found to be compared satisfactorily with the recorded pan evaporation data. The results of the estimated Ep values for different months, the variations of relative errors in different months, the values of mean monthly differences between recorded and estimated Ep, and the comparison between the models annual Ep with the recorded annual Ep, using these models suggest that the Penman–Monteith model can be selected as the best model in Ep estimation in the Muda Irrigation Project, Malaysia. The FAO-PM method can be considered as the second best model, successively followed by the Blaney–Criddle method, modified Penman method, and Christiansen method. Thus, the results of the Penman–Monteith model can be interpreted as the validation of the Ep model and can safely be used in ETp estimation in the Muda Irrigation Project, Malaysia.