CHARACTERISTICS OF EVOLUTION OF POTENTIAL EVAPORATION IN TIANJIN REGION OF CHINA

The characteristics of seasonal and annual changes of potential evaporation, the variations of thermal and dynamical evaporation in different seasons and the relationships between potential evaporation and meteorological elements were analyzed according to the observed data of 9 stations from 1961 to 2001 in the Tianjin region of China. Analyses indicate that thermal evaporation is the main part of the potential evaporation and offers about 90% fraction of to it in summer, while in winter the dynamical evaporation is greater than the thermal one, especially in Jan., offering 100% contribution, that the influence of temperature on the change of potential evaporation was much larger than that of wind, vapor pressure and sunshine duration, and potential evaporation increased by 30.33mm with temperature raise 1℃, and that potential evaporation had a surprising increasing tendency, in particular during the recent decade, with the velocity of4.22mm/a. The potential evaporation in the Tianjin region will be higher than the past, especially on the global warming background, so that it has the great effects not only on the climatic forcing changes, but also on development of city and economy.