Observation Of Energy Partitioning And Simulation Of Lake Evaporation Over A Lake In The Badain Jaran Desert

Evaporation is the key factor of water cycle in arid regions.110 lakes in the hinterland of the Badain Jaran Desert which are little influenced by human activities offered the ideal place to study the energy partitioning and evaporation law of water surface under extreme drought conditions.Evaporation is the main way of drainage of lake water,and it is also the key factor to quantitatively study the source of groundwater in the hinterland of the desert.However,due to the lack of the observation on land-atmosphere interaction,detailed and continuous integrated observation data this area,the researches on the basic scientific problems such as energy partitioning and evaporation law over the lake in the hinterland of desert are insufficient and lead a great difference in understanding of evaporation law in former studies.Combined with the integrated observation experiments of land process and hydrological cycle of the lake group in the Badain Jaran Desert,the study mainly used the eddy covariance technique to observe the energy partitioning and meteorological elements over the lake surface and to reveal the energy and water vapor exchange between the water surface and the atmosphere in the hinterland of the the Badain Jaran Desert in different time scales.In order to simulate,evaluate and analyze the evaporation of lake in different time scales,methods to simulate the evaporation of lakes in the desert hinterland is obtained by combining the date of meteorological station over the lake and data of meteorological station and evaporation pan in the periphery of the desert.The main conclusions of this study are listed bellow,(1)Eddy covariance technique can be used for long-term and effective observation of energy flux and water vapor flux over the lake in the hinterland desert.The total energy closure ratio(EBR)of the whole year is 1.39.The instrument error and the freezing and melting of lakes process in winter have influences on the observation of latent heat flux;the EBR is 1.32 without data in winter(December,January and February),and the turbulent flux is above 30%of the available energy in the year.The energy unclosure problem of the lake should be attributed to advection exchange between the lake and surrounding sand dunes;(2)There are obvious seasonal changes in the net radiation flux(R_n),latent heat flux(?E)and sensible heat flux(H).The daily average R_n is positively correlated with daily average?E,and is negatively correlated with daily average H.The latent heat flux is the mainly energy flux over the lake surface.From August 2012 to July 2013,the annual average?E is 119.7 W/m~2,while the annual average H is only 8.2 W/m~2;(3)The changes of daily average wind speed(u),air temperature(T_a),lake surface temperature(T_s)and saturated vapor pressure defict(VPD)are positively linear correlated with the change of latent heat flux.Through multiple linear regression analysis,the equations containing R_n,T_a,u and VPD can simulate the change of the latent heat flux of the lake well;by using 30 minutes data in 24hours,the change of?E relative lag to R_n and T_a in 2~3 hours,the influence of u on E is the largest;(4)By using the data from the lake meteorological station in the desert hinterland,the evaporation model can simulate the changes of the lake evaporation well,and the daily evaporation from eddy covariance technique and daily evaporation calculated by the Penman 1948 equtaion and the PT equtaion has a more consistent variation trend on the seasonal scale.By using the Penman1948 equtaion,the lake simulation has the best effect.When the PT equtaion is used,due the strong advection exchange in the desert lakes,?PT is 1.78 can be better use to simulate the lake evaporation;(5)The variation of the daily evaporation from evaporation pan in the Alxa right banner meteorological station is linearly related to the variation of daily evaporation observed by eddy covariance technique over the lake in desert hinterland,and the pan evaporation in the Alxa right banner meteorological station can be used to estimate the evaporation of the lakes in desert hinterland in the past few decades;(6)The"evaporation paradox"was exit in the Alxa right banner with the average temperature and sunshine duration increasing and pan evaporation dreasing during 1966 to 2013,which was mainly due to the decrease of wind speed.