Validation and Comparison of the Simulation at Zoigê Station during Freezing and Thawing with Land Surface Model CLM

The community land model (CLM) is a highly developed and widely used land surface model. Two sets of simulation experiments were respectively conducted with model versions 3.0 and 4.0 by using observational data of Zoigê station of the Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences. A comparison of the observation and simulation results of soil physical quantities such as temperature and moisture verified the applicability of the model in the seasonal frozen soil area of the plateau. Simulations of CLM4.0 showed a significant improvement over CLM3.0. CLM4.0 includes a parameterization scheme of unfrozen water. Therefore, the model can simulate the unfrozen water in frozen soil, which improves the simulation of soil water content during freezing and thawing while reducing the soil ice content. Because unfrozen water increases the heat capacity and decreases the thermal conductivity of frozen soil, the simulation of soil temperature is correspondingly improved. However, the simulated temperature of the deeper soil was significantly lower than observation during the freeze-thaw period. The number of simulated soil water surges in the ablation stage and decreases in the freezing stage were both improved compared with observation. In addition, the simulated time of ablation and freezing processes were both shorter than those of observation, whereas the time of complete frozen and complete ablation were longer. Therefore, the simulation ability of CLM for frozen soil areas of the plateau requires improvement.