Summary:

## Excess Ground Ice Parameterization

This section describes an optional parameterization for modeling the effects of excess ground ice melt and soil subsidence in the land surface model.

Key Points:

1. Initial excess ground ice concentrations are derived from previous research.

2. When excess ground ice is present, the soil depth for each layer is adjusted based on the amount of excess ice.

3. After adjusting the layer depths, the soil temperature equations and thermal properties are recalculated using the updated depths and ice content.

4. Soil subsidence at each time step is calculated as the difference in layer depths between the current and previous time steps.

5. Excess ground ice is treated similarly to normal soil ice in terms of hydraulic conductivity and thawing/refreezing processes.

6. When a soil layer thaws, excess ground ice is only allowed to melt when no normal soil ice is present. When a layer refreezes, liquid soil water can only turn into normal soil ice, and no new excess ice can be created.

7. The excess liquid soil moisture from excess ice melt is distributed within the soil column according to the lateral sub-surface runoff scheme.

The article provides the detailed mathematical formulations and equations used to incorporate the effects of excess ground ice in the land surface model.