The Improvement Of The Exponential Evapotranspiration(ET)Model And Simulation And Application Of The Surface ET

Evapotranspiration(ET) is the important procedure of water cxchange bewteen atmosphere and land surface, It is very important and has high scientifical value for drought monitoring,hydrology drought monitoring, distribution and of water resources, Farming operation management and evaluate climatic variation to accurately simulate evapotranspiration.This essay plan to bring about a exponential ET model by all remote sensing data,and improve the model.What’s more,improving the resolution of the model,making it better to be used in large area about the evapotranspiration monitoring,and to drought monitoring’s service. The main results are as follows:(ⅰ)The improved model is ET=-3.928Rn(T+18/DTsR)0.14exp(0.401EVI2) and it’s primary input data are land surface radiation,EVI,land surface temperature and land surface temperature diurnal variation.Its spatial resolution is0.25°×0.25°.The exchange for NDVI with EVI,can effciently avoid the saturation of NDVI on high vegatation coverage area.(ⅱ)To fairly assess the accuracy of the improved exponential ET model’s ET estimation,we randomly divided the21flux towers into two groups and performed a series of cross-validations.The square of correlation coefficients(R2),the bias and the Root Mean Square Error(RMSE) of the comparison between the groud-measured and estimated daily ET fromm the second group of flux towers,using the first group data are0.84,4.98W/m2and49.12W/m2,respectively.The result of the otherwise are0.778,4.24W/m2and46.775W/m2.What’s more,we chosen5sites over the global,compared the simulated ET with ground measured ET,the range of R2is 0.71-0.86.Show that the Show that the revised model to simulate ET and the actual observed ET has good consistency.(iii) Based on the improved expoential ET model,we calculated the EDI and compared it with PDSI’s time change curve.Visibly,we can found the improved ET model can reflect the distribution of ET and its change trend,will play its role in the actual drought monitoring job.(iv) Using the improved expoential ET model to simulate the land surface evapotranspiation during April to Sepember of2006-2007,and also the quarterly land surface evapotranspiation for spring to autumn of2006-2007.Based on these,we analysis the distribution of the land surface evapotranspiation of China:the smaller value of land surface evapotranspiation often in northwest district,and there is a high frequency of spring smaller value in northeast.(v)Using the improved model monitoring the drought process in north China and northeast of China,respectively.And compared the EDI with PDSI.The result shows:R2were0.72～0.92,0.66～0.77.There is a good consistency between EDI and PDSI, the improved model can accurately simulte the drought level and develop tendency of land surface and this model has a good apply prospect on real drought monitoring.