Evaporation Paradox in the Yellow River Basin

Based on the data of 72 meteorological stations in the Yellow River Basin from 1960 to 2010,this paper analyzed the changing trends in potential evapotranspiration and air temperature,and the main factors affecting the decrease of potential evapotranspiration.It also discussed the existence of theevaporation paradox(the contract between expectation and observation of evaporation).The results are indicated in the following aspects.(1)In the past 51 years,the air temperature increased significantly and the potential evapotranspiration decreased,therefore the evaporation paradox actually existed in the Yellow River Basin.(2) Theevaporation paradoxis not consistent spatially or temporally:as the temperature increased,potential evapotranspiration decreased in spring,summer and winter over most parts of Shanxi and Henan,and some parts of Gansu,Ningxia,Inner Mongolia,and Shaanxi. In the past 51 years,the changing trend of potential evapotranspiration is not significant from 1960 to 1979,and the changing trends of temperature and the potential evapotranspiration were negatively correlated at most of the stations.(3)In the past 51 years,the changing trends of annual,summer and autumn precipitation are not obvious,and the precipitation and potential evapotranspiration exhibit a contrary trend.(4)In terms of the contribution rate of meteorological elements change to potential evapotranspiration change,a significant decrease of wind speeds in the 51 years is the dominating factor leading to the decrease of potential evapotranspiration in the Yellow River Basin.