Changes of pan evaporation in China in 1960-2000

Based on the observational data of 664 meteorological stations in China from 1960 to 2000 and combined with the geographic information system(GIS) of Arc GIS,the spatial and temporal distributions and their trends for pan evaporation in China are investigated in this study.The results indicate that,from 1960 to 2000,the rate of pan evaporation steadily decrease in China.Compared with the period of 1960s to 1970s,the rate of annual pan evaporation during 1980s to 1990s decreases by 99.8 mm or 5.8%.The seasonal analyses show that the decrease of pan evaporation occurs mainly in spring,summer and winter.The spatial distribution of the change rate shows that the decrease of pan evaporation mainly occurs in East and Central South of China.Further analysis shows that the decrease of pan evaporation is closely related to the reduction of the solar irradiance resulting from the sun-shine percentage decrease.