Assessment of the Influences of Different Potential Evapotranspiration Inputs on the Performance of Monthly Hydrological Models under Different Climatic Conditions

Potential evapotranspiration (PET), which determines the upper limit of actual evapotranspiration (AET), is a necessary input in monthly hydrological models. In this study, the sensitivities of monthly hydrological models to different PET inputs are investigated in 37 catchments under different climatic conditions. Four types of PET estimation methods (i.e., Penman Monteith, Hargreaves Samani, Jensen-Haise, and Hamon) give significantly different PET values in the 37 catchments. However, similar runoff simulations are produced based on different PET inputs in both nonhumid and humid regions. It is found that parameter calibration of the hydrological model can eliminate the influences of different PET inputs on runoff simulations in both nonhumid and humid regions. However, the influences of parameter calibration on the simulated water balance components, including AET and water storage change (WSC), are different in nonhumid and humid regions. In nonhumid regions, simulated runoff, AET, and WSC are similar using different PET inputs. In humid regions, simulated AET and WSC using different PET inputs are significantly different, and simulated runoff and the sums of AET and WSC are similar to each other. It is suggested that the choice of PET inputs for monthly hydrological models be based on the selected region and the relevant hydrological practices. In runoff modeling, different PET inputs can produce similar runoff simulations in both nonhumid and humid regions. However, when estimating AET and WSC in humid regions, different PET inputs will result in significantly different AET and WSC simulations, which should be noted by model users.