Potential Evapotranspiration Model for Muda Irrigation Project, Malaysia

Methods to estimate free-surface evaporation E (p) and potential evapotranspiration ET (p) 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 E (p) using these models show that the E (p) 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 E (p) values for different months, the variations of relative errors in different months, the values of mean monthly differences between recorded and estimated E (p) , and the comparison between the models annual E (p) with the recorded annual E (p) , using these models suggest that the Penman-Monteith model can be selected as the best model in E (p) 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 E (p) model and can safely be used in ET (p) estimation in the Muda Irrigation Project, Malaysia.