Temporal And Spatial Structure Of Variations Of Actual Evapotranspiration And The Analysis Of The Impact Factors Over The Yangtze River Basin Nearly50Years (1960-2010)

Global climate change will inevitably cause changes in the hydrological cycle, resulting in the re-allocation of water resources in spatial and temporal and cause changes in the amount of water resources, which further affect the water resources, Earth’s ecological environment and the economic development of human society. Evapotranspiration is the important link of hydrologic cycle and water conversion, while it is also the comprehensive reflection of various kinds of the of single climate factor, such as solar radiation, temperature, wind speed, precipitation, aerosol, etc. Study for the change characteristics of evapotranspiration in the river basin will have far-reaching significance to some important scientific question about regional climate change, water cycle and water resources management, etc.Based on the ground-based observation data from147meteorological stations nearly50years over the Yangtze river basin, applying advection-aridity (AA) model that through parameters validation with water balance validation method and general circulation model (ECHAM5/MPI-OM), calculating the actual evapotranspiration,researching the tendency and regulation of temporal and spatial variation about the actual evapotranspiration from1960to2010, analysing and exploring effects contribution of the meteorological factors that affecting the actual evapotranspiration changing (net radiation, temperature, saturated vapor pressure difference, wind speed).The main conclusion of paper are as follows:(1) AA model,through the water balance validation, has higher precision. The estimating effect of AA model is good, the estimating effect of actual evaporation in the mid-lower reaches is better than estimation in the upper reach. Although,absolute error of the simulated results of ECHAM5is larger, the simulation results about change trend of actual evapotranspiration over the Yangtze river basin is the same as the estimating result of AA model.(2)The significant decreasing trend of actual evapotranspiration were detected in the whole basin, the climate changing rate is about-6mm/10a(through the99%significant level inspection). The decreasing trend of inter-annual variability and seasonal variability about actual evapotranspiration in the upper reach is more significant than the decreasing trend in the mid-lower reaches. Decreasing of annual actual evapotranspiration is mainly due to decreasing of actual evapotranspiration in spring, summer, autumn, while decreasing level of actual evapotranspiration is also the largest amount in spring. (3)Variation relationship of net radiation and actual evapotranspiration show highly significant positive correlation, and their changing trend are consistent. Decreasing of net radiation has an important impact on the decreasing of actual evapotranspiration over the Yangtze River basin.(4) The variation of temperature and saturated vapor pressure difference show increasing trend, present contrary changing trend compared with actual evapotranspiration. The variation of Temperature and actual evapotranspiration present negative correlation relationship as well as The variation relationship of actual evapotranspiration and saturated vapor pressure difference. Therefore, neither temperature rising nor saturated vapor pressure difference increasing does not have a significant impact on the actual evapotranspiration changing over the Yangtze River basin.(5) Changing trend of wind speed and actual evapotranspiration are consistent, while variation difference of temporal and spatial of changing trend of them is larger, it makes a negative correlation relationship between them. So, wind speed decreasing does not have a significant impact on the actual evapotranspiration changing over the Yangtze River basin.