Comparison of Ten Potential Evapotranspiration Models and Their Attribution Analyses for Ten Chinese Drainage Basins

Potential evapotranspiration (E-PET) is usually calculated by empirical methods from surface meteorological variables, such as temperature, radiation and wind speed. The in-situ measured pan evaporation (ETpan) can also be used as a proxy forE(PET). In this study,E(PET)values computed from ten models are compared with observed ET(pan)data in ten Chinese river basins for the period 1961-2013. The daily observed meteorological variables at 2267 stations are used as the input to those models, and a ranking scheme is applied to rank the statistical quantities (ratio of standard deviations, correlation coefficient, and ratio of trends) between ET(pan)and modeledE(PET)in different river basins. There are large deviations between the modeledE(PET)and the ET(pan)in both the magnitude and the annual trend at most stations. In eight of the basins (except for Southeast and Southwest China), ET(pan)shows decreasing trends with magnitudes ranging between -0.01 mm d(-1)yr(-1)and -0.03 mm d(-1)yr(-1), while the decreasing trends in modeledE(PET)are less than -0.01 mm d(-1)yr(-1). Inter comparisons among different models in different river basins suggest that PET(Ham1)is the best model in the Pearl River basin, PET(Ham2)outperforms other models in the Huaihe River, Yangtze River and Yellow River basins, and PET(FAO)is the best model for the remaining basins. Sensitivity analyses reveal that wind speed and sunshine duration are two important factors for decreasingE(PET)in most basins except in Southeast and Southwest China. The increasingE(PET)trend in Southeast China is mainly attributed to the reduced relative humidity.