Estimation Of Evapotranspiration Based On Maximum Entropy Production Principle And Calculation Of Water Balance In Horqin Sandy Land

Evapotranspiration(evapotranspiration,ET),as the only hydrological parameter involved in both water cycle and enerey cycle,has been an important part of hydrological research in arid areas.Horqin sandy land is one of the most serious desertification areas in northern China,it is of great significance to reveal the temporal and spatial variation characteristics of evapotranspiration and the change law of water balance in Horqin sandy land for desertification control.Using Landsat8 remote sensing data,GPM precipitation data and GLDAS soil moisture data evapotranspiration model based on maximum entropy production principle(MEP)model and water balance method,the surface parameters,evapotranspiration and water balance in Horqin sandy land typical area were estimated.The inversion results are verified by voiticity measured data,meteorological data and SEBAL model simulation data.On this basis,the temporal and spatial changes of surface parameters,ET,precipitation and soil water content under different land cover types are analyzed,and the followinu conclusions are obtained:The main results are as follows:(1)Compared with the measured data,the error between sensible heat flux and soil heat flux is relatively large,but the error between daily ET and latent heat flux is small.it is found that the simulated value is lower than the measured value by using 2014-2016 MEP model and SEBAL model to simulate the measured daily ET of daily ET.The accuracy of surface parameters as model input data is relatively high,in which the highest fitting coefficient of surface net radiation is 0.98,the lowest relative error is 0.03.The daily ET of SEBAL model was higher than that of MEP model.The fitting coefficient of the two models is 0.83,which is verified by the measured data,which shows that the two models have high accuracy for daily ET estimation,and there is a great difference between the individlal date SEBAL model and the MEP model in dune land.When the error is within 1mm,the MEP model can provide a relatively reasonable daily ET estimation for the study area.(2)The temporal and spatial distribution of surface parameters and ET under different land cover types is similar to that of ET,surface net radiation and normalized vegetation index,which is the highest in lakes,followed by farmland and meadow.The dunes are the lowest,However,due to the different types of dunes,the fixed dunes and semi-tixed dunes show a trend higher than the mobile dunes,showing a trend of gradually decreasing from the lake as the center to the surrounding areas,and the dunes show a trend that the fixed dunes and semi-fixed dunes are higher than the mobile dunes.The surface temperature and surface albedo showed the opposite trend in different land cover types and surface net radiation,the relative humidity was obviously different in different dates and different land cover types,and the regularity was not strong.The relative humidity of the lake is high,farmland and meadow fluctuate greatly,the surface parameters are consistent with the variation of ET in time,showing an upward trend from May to August and a downward trend from September to October.The main factors affecting evapotranspiration and surface paraleters are:different water supply conditions of different land cover types,different vegetation types and vegetation quantity,human activities,changes of meteorological elements.(3)There is a good response between vegetation index and ET,and vegetation index will fluctuate with the change of ET,which is affected by vegetation quantity and growth status.Different vegetation indexes have different response with precipitation and ET in sand dunes and meadows.GCC,NDVI and coverage have relatively poor response relationship with ET in sand dunes,and GCC and NDVI have the closest relationship with ET in meadow.Dune precipitation and ET have the highest correlation with GCC,meadow coverage and ET have a good correlation,comprehensive analysis of GCC and coverage and ET correlation is the highest,the correlation is good.(4)The simulated values of GPM precipitation data and GLDAS soil water content data are lower than the measured data,the temporal and spatial distribution of precipitation in Horqin sandy land is uneven.The average precipitation in growing season is between 260-475mm,and soil water content is smaller with the increase of soil layer thickness,mainly because precipitation and evaporation have little disturbance to deep soil water content.The soil water content at 0-200cm in the growth season of the study area is between 280-340mm as a whole,the change of surface water reserves is large,and the whole is in a reduced state.