Snow pack area coverage

When the snow storage is small, snow will not cover the enter cell area. Rather, the snow will be concentrated in sheltered areas. If a small snow thickness was spread out over the entire cell area, then melting would occur too quickly. Thus, MIKE SHE also includes a snow coverage function, where you provide a minimum snow depth for which you can assume that the entire cell is covered with snow. For snow depths less than this minimum, the area fraction is linearly reduced to zero when the snow storage goes to zero. Thus, the area factor, Af, is

(22.10)   

where S_T is the total snow storage (wet + dry) and S_min is the minimum snow depth for full area coverage.

The melting/freezing rates are multiplied by the area factor before being applied. Furthermore, if the area factor is less than one, then the precipitation and ET is distributed between the snow and the normal ground surface based on the area factor.