Summary:

## Soil Hydrology

The article discusses the calculation of the combined water and ice soil volume fraction in a soil layer, denoted as θ_i. This fraction is given by the equation:

θ_i = (1/Δz_i) * (w_ice,i/ρ_ice + w_liq,i/ρ_liq)

Where:
- Δz_i is the soil layer thickness
- w_ice,i is the ice mass
- w_liq,i is the liquid water mass
- ρ_ice and ρ_liq are the densities of ice and liquid water, respectively.

If the calculated θ_i is less than the soil's saturation volume fraction θ_sat,i, then the liquid water mass is adjusted to:

w_liq,i = (θ_sat,i * Δz_i - w_ice,i/ρ_ice) * ρ_liq

However, if excess ice is melting and the liquid water mass exceeds the saturation volume, the water in the layer is reset to:

w_liq,i = θ_sat,i * ρ_liq * Δz_i

This allows excess ice to be initialized and lost only after the pore ice has melted, which is a realistic scenario if the excess ice is found in heterogeneous chunks.