Abstract: Based on the measuring data from 115 meteorological stations between 1961 and 2000 in the Yangtze River Basin, pan evaporation (PE), reference evapotranspiration (ETr) and actual evapotranspiration (ETa) as well as their trends are calculated and analyzed. The results indicate that significant decreasing trends of PE, ETr and ETa are detected in the upper, middle and lower as well as the whole Yangtze River Basin, especially in summer. No significant trends for PE, ETr and ETa are detected in spring and autumn. PE and ETr in winter show significant negative trends, while ETa shows a significant positive trend in winter. The spatial distribution of this kind of negative trends over the middle and lower reaches of the Yangtze River is more significant than that over the upper reaches. However, at the same time the air temperature shows a significantly increasing trend, which will increase evapotranspiration. A thorough investigation shows that the significant decrease exists in net radiation and wind speed over the Basin, which, in turn, may cause the decrease in evapotranspiration after compensating the increase in air temperature.

Key words: pan evaporation, reference evapotranspiration, actual evapotranspiration, spatial and temporal distribu