3.3 Determination of the water vapor mass trajectory
In order to better estimate the contribution rate of lake evaporation in the Xiying Reservoir, our research first judged the characteristics of the movement path of the advection water vapor which affects the precipitation of Xiying Reservoir, so as to determine the initial value of advection water vapor. Therefore, this research used TrajStat software and the global data assimilation system data for calculation of airflow backward trajectory at 500m height of the Xiying Reservoir for 72 hours during sampling period based on HYSPLIT Model. The Angle Distance algorithm was used to cluster all the air mass trajectories.