Summary:

## Surface Water Storage

The CLM4.5 model includes a surface water store to represent wetlands and small, sub-grid scale water bodies. The key aspects of this module are:

### State Variables
- Mass of surface water (Wsfc, kg/m^2)
- Surface water temperature (Th2osfc)

### Surface Water Storage and Outflow
- Surface water storage is determined by the microtopography, assumed to have a normal distribution around the grid cell mean elevation.
- The fraction of the grid cell that is inundated (fh2osfc) is calculated based on the microtopographic standard deviation (σmicro).
- When the inundated fraction exceeds a critical threshold (fc), the surface water acts as a linear reservoir, with outflow (qout,h2osfc) proportional to the connected inundated fraction (fconnected).
- The linear storage coefficient (kh2osfc) is a function of the grid cell mean topographic slope.

### Microtopography Parameterization
- The microtopographic standard deviation (σmicro) is parameterized as a function of the grid cell slope, with adjustable parameters σmax and η.
- In the absence of global microtopography data, this simple parameterization is used.