Trend of potential evapotranspiration over China during 1956 to 2000
19562000年中国潜在蒸散量变化趋势

This study aims at providing a climatological reference of potential evapotranspiration for the second comprehensive assessment of water resources and water resource planning of China.Based on the climatic data from 580 stations throughout the country during 1956 and 2000,potential evapotranspirations are calculated using the Penman-Monteith Method recommended by FAO.The spatial and temporal distributions of the potential evapotranspiration over China and the temporal trends of the regional averages for 10 major river basins and whole country are analyzed.Through a partial correlation analysis,the major climate factors which affect the temporal change of the potential evapotranspiration are also analyzed.Major results are as follows: 1) The seasonal and annual potential evapotranspiration for China as a whole and for most of the basins show declining tendencies during the past 45 years;for the Songhua River Basin there appears a slightly increasing trend.2) Consequently,the annual potential evapotranspirations averaged over 1980-2000 are lower than those for the first water resources assessment period(1956-1979) in most parts of China.Exceptions are found in some areas of Shandong Peninsula,river basins in central and western parts of Southwest China,Ningxia Hui Autonomous Region as well as source regions of the Yangtze River and the Yellow River,which may have brought about disadvantages to the exploitation and utilization of water resources.(3) Generally),sunshine duration,wind speed and relative humidity have greater impact on the potential evapotranspiration than temperature.Decline tendencies of sunshine duration and/or wind speed at the same period appear to be the major causes for the negative trend of the potential evapotranspiration in most areas.