Evapotranspiration Estimation And Its Impact Factors In The Three River Headwater Region

The resource of China’s main rivers is the Three-River HeadwatersRegion(TRHR)which is also regarded as the important ecological zone for China and even for the world.Therefore,it is significant for regional climate and water resource allocation to keep the balance of ecological environment.In research area,evapotranspiration(ET)is the major way of discharge of surface water and groundwater.The study on it can reflect the changes of water resource and ecological environment,which will be valuable on the regional development.Based on MODIS remote sensing data,the ET was estimated afer MRT processing.Besides,the temporal and spatial variation of ET with its influence factors was also studied in the TRHR from 2001 to 2015.And the ET coefficient was determined using the statistical results of 13 meteorological stations.Moreover,the calculation results was verified using the principle of close basin water budget.According to the estimation of regional ET,with a view to the pratical situation,the ecological water demand was analyzed under the current situation(in2015).The results indicated that:(1)In terms of evapotranspiration,the annual actual ET of TRHR variedfrom 2001 to 2015 with the maxmum value 636.51 mm in2009and minimum value 535.01 mm in 2015.(2)Study on seperated zones shows that the three area were highly similar in the trend of ET.The rank of anual ET account is illustrated as Lancang River>Yellow river>Yangtzeriver(3)On the basis of the evaporation statistics in 13 meteorological stations,the evaporation coefficient was0.5923 in the whole study area.(4)The estimation of SEBS ET is identical to the sum of water consumption and precipitation,which is explained the rationality of model application in TRHH.(5)ET in TRHR has obvious correlation with temperature and precipitation and increases with the increasing NDVI.(6)In the current circumstance(in 2015),the ecological water requirement is 1875.75×10~8m~3 in TRHR,which includes 464.59×10~8 m~3 of Yellow river region,910.16×10~8 m~3 of Yangtze river and237.33×10~8 m~3 in Lancang River.