The Analysis Of Soil Thermal Conductivity And The Influence On Calculation Of Soil Heat Flux In Mu Us Bottomland

Soil thermal conductivity is one of the important thermodynamic characteristics that reflects the thermal conduction of soil.It is widely used in energy engineering,soil science,agricultural meteorology and other disciplines.The study of the variation of soil thermal conductivity with water content and temperature is used to improve calculation precision of soil heat flux.The Mu Us bottomland is located in arid and semi-arid region.The daily temperature difference is large,and the summer solar radiation is sufficient.However,the thickness of the vadose zone is small,and the depth of the groundwater level is shallow.Therefore,the accurate calculation of soil heat flux has important scientific and practical significance for the rational development and utilization of regional groundwater resources and ecological environmental protection.This article is guided by the basic theory of soil physics and soil hydrodynamics,using in-situ monitoring,laboratory experiments,theoretical analysis and calculation,etc.,based on the soil thermal conductivity model,using calorimetry method and temperature gradient method to calculated the soil heat flux.The soil heat fluxes at different depths and the interannual changes are discussed.The main conclusions were obtained:（1）The numerical model of the change of soil thermal conductivity with water content at room temperature is improved,and a large number of measured data are used to verify the model at room temperature.The RMSE are 0.115,0.118,0.097 for data measured by Lu（2007）,Karsubuchi（2003）and Mc Inne（1981）,respectively.（2）The model of the normalized thermal conductivity with water content and temperature was analyzed and established,and the parameters of model were fitted according to the relevant measured data.For a specific water content,the normalized thermal conductivity changes exponentially with temperature.（3）Based on the KDII-pro thermal parameter analyzer,the thermal conductivity with water content at 5,15,25,40,and 60℃were measured and analyzed.Using the thermal conductivity models calculated the RMSE of the measured and calculated values based on the parameter fitting at different temperatures.The RMSE are 0.138and 0.081,0.091 and 0.085 W m^-1K^-1 for four soils,respectively.（4）Using the thermal conductivity model improves the calculation accuracy of soil heat flux at different temperatures.The errors and influencing factors of sine wave method,temperature gradient method,calorimetry method and heat conduction convection method in calculating soil heat flux are analyzed.（5）The surface heat flux and deep soil heat flux were calculated using calorimetric method and temperature gradient method,respectively.The data show that the heat transfer from the vadose zone to the atmosphere is 20MJ m^-2,and the heat transfer upward from the soil below 87cm depth is 4.5MJ m^-2 throughout 2018.