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 (ET pan ) can also be used as a proxy for E 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 modeled E PET in different river basins. There are large deviations between the modeled E 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 modeled E 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 decreasing E PET in most basins except in Southeast and Southwest China. The increasing E PET trend in Southeast China is mainly attributed to the reduced relative humidity.