• landscape frozen fraction;
  • snow cover fraction;
  • soil impermeability;
  • hydrological cycles;
  • high-latitude regions;
  • CLM4

[1] Snow cover at high latitudes is an excellent natural insulator that can maintain the underlying ground at a higher temperature than the overlying atmosphere. Soil impermeability usually varies when snow cover accumulates, which is closely related to soil and landscape freeze/thaw status. How snow cover affects the landscape frozen fraction and soil impermeability and how this impermeability regulates hydrological processes in cold regions have not been fully assessed and quantified. In order to understand these processes, this study performed a series of experiments by using the Community Land Model version 4 (CLM4). We first simulated the top-soil-layer ice, snow ice, and canopy ice to calculate the landscape frozen fraction, which was evaluated based on the Special Sensor Microwave/Imager (SSM/I) observed landscape freeze/thaw earth system data record (FT-ESDR) in two selected regions at high latitudes. Then two soil impermeability parameterizations were validated against various in situ and satellite observations. The results suggest the following: (1) compared to SSM/I FT-ESDR, CLM4 can capture the overall landscape freeze/thaw status in the regions north of 60°N in boreal winter and spring; (2) as the snow cover fraction approaches unity, the CLM4-simulated landscape frozen fraction is mainly controlled by the snow ice amount, resulting in step changes between SSM/I FT-ESDR observed and CLM4-simulated landscape frozen fractions; and (3) in most of the cold regions, the timing of the boreal spring runoff simulations is improved by reducing the impermeable area in high landscape frozen fraction regions.