干旱区生态环境知识资源中心

Evaporation, an important component of the water cycle, is a critical variable in the determination of local water resources available. This paper selected two meteorological stations at Beijing and Tianjin as case study sites. Based on the time series of daily meteorological data from 1958 to 2008, the potential evaporation is calculated by the Penman formula, and the variations of meteorological variables (air temperature, sunshine hour, relative humidity, wind speed) were investigated. The results revealed that: (I) the annual potential evaporation at Beijing showed an increasing trend, while that in Tianjin showed a decreasing trend, and that the air temperature at the two stations both increased significantly; (2) sunshine hours, relative humidity and wind speed presented a decreasing trend at the two stations; and (3) relative humidity and wind speed are the key factors affecting the potential evaporation at Beijing and Tianjin, respectively. The results of this paper provide a valuable reference for the forecast of future water resource availability, and the sustainable development and utilization of water resources in the arid and semi-arid region.