A Study of Soil Thermal and Hydraulic Properties and Parameterizations for CLM in the SRYR

Located in the northeast part of the Qinghai-Tibet Plateau, the source region of the Yellow River is a crucial water conservation area. Laboratory tests and observations are used to determine the soil thermal and hydraulic properties in this key area. Furthermore, their physical processes in the Community Land Model (CLM) are revised to better apply to the plateau. The main results are as follows. (1) The thermal conductivity in frozen soil is mainly controlled by the content of air and is positively correlated with subzero temperatures (-5 to -20 degrees C); however, it slightly increases with increasing temperature (5 to 20 degrees C) in thawed soil, and obvious layering exists. The influence of temperature can be ignored for dry soil. (2) The thermal conductivity of thawed soil is positively correlated with water content and shows a nonlinear variation. The rate of increase is rapid during the early stage of thawing and then slows. (3) The saturated hydraulic conductivity decreases with depth. Soil matric potential exhibits large fluctuations and is spatially heterogeneous due to the feedback to soil moisture. (4) The simulation differences of soil temperature and moisture are narrowed to approximately 1 degrees C and by half, respectively, by the revised schemes in CLM4.5. The simulation of energy fluxes and ground temperature also improved, but the latent heat flux performed less well due to the deficiencies in the hydraulic schemes. This study is of great significance for research on land surface processes and the application of the CLM in the Qinghai-Tibet Plateau.