Relationship between variation of evapotranspiration and ecological deterioration in source region of Yellow River

Using hydrological and meteorological data from the source region of the Yellow River from the 1980s onward,the variation trends of the evapotranspiration,sunshine duration,air temperature and air saturation deficit were analyzed.The influences of various factors on the evapotranspiration are highlighted. The results show that evapotranspiration in the source region of the Yellow River is increasing year by year.The sunshine duration,regarded as the main factor,is increasing at a rate of 3.6 h/a.The air temperature is increasing at a rate of 0.04℃/a.The air saturation deficit is increasing at a rate of 0.02 hPa/a.The increases of the sunshine duration,air temperature and air saturation deficit accelerate the evapotranspiration from the grassland,and the deterioration of the ecological environment also increases the evapotranspiration.The increase of the evapotranspiration and the decrease of the precipitation amount have a direct influence on the decrease of the flow discharge and the ecological deterioration in the source region of the Yellow River.