A New Frozen Soil Parameterization Including Frost and Thaw Fronts in the Community Land Model

Freeze-thaw processes in soils, including changes in frost and thaw fronts (FTFs), are very sensitive to warming. However, the latest climate models do not predict changes in FTFs directly. In this study, a new frozen soil parameterization including changes in FTFs was incorporated into the Community Land Model version 4.5 for climate modeling, which we denote CLM4.5_FTF. A set of numerical experiments including single points, regions in China, and a global scale were conducted using the model to validate its performance. The simulated FTF depths compare well with observed data from both the D66 station (permafrost) and Hulugou station (seasonally frozen ground). The simulated active layer thickness, defined as the maximum thaw front depth in permafrost, is in general agreement but slightly greater than observations from the Circumpolar Active Layer Monitoring program. The simulated distributions of different types of frozen soil in China and permafrost in the northern hemisphere are in agreement with the frozen soil map of China and the International Permafrost Association map, respectively. The results confirm that the model performs well for FTF simulations. The model was also used for year-long simulations of soil temperature and freeze-thaw processes to check its applicability in continuous simulation. The results show that CLM4.5_FTF performed better than the original model, and the improvement was better for lower levels than for the upper level. Finally, we give simulated latent heat flux, sensible heat flux, and 10-cm soil temperature deviations determined via the couple model with and without the new scheme.