An improved model for predicting soil thermal conductivity from water content at room temperature

The thermal conductivity and water content relationship is required for quantitative study of heat and water transfer processes in saturated and unsaturated soils. In this study, we developed an improved model that describes the relationship between thermal conductivity and volumetric water content of soils. With our new model, soil thermal conductivity can be estimated using soil bulk density, sand (or quartz) fraction, and water content. The new model was first calibrated using measured thermal conductivity from eight soils. As a first step in validation, predicted thermal conductivity with the calibrated model was compared with measured thermal conductivity on four additional soils. Except for the sand, the root mean square error (RMSE) of the new model ranged from 0.040 to 0.079 W m(-1) K-1, considerably less than that of the Johansen model (0.073-0.203 W m(-1) K-1) or the C (o) over cap te and Konrad model (0.100-0.174 W m(-1) K-1). A second validation test was performed by comparing the three models with literature data that were mostly used by Johansen and C (o) over cap te and Konrad to establish their models. The RMSEs of the new model, the Johansen model, and the C (o) over cap te and Konrad model were 0.176, 0.176, and 0.177 W m(-1) K-1, respectively. The results show that the new model provided accurate approximations of soil thermal conductivity for a wide range of soils. All of the models tested demonstrated sensitivity to the quartz fraction of coarse-textured soils.