MIKE SHE includes a comprehensive snow melt module based on a modified degree-day method. If the Include snow melt (V1 p. 229) checkbox is checked then rain accumulates as snow if the Air Temperature (V1 p. 236) is below the Threshold Melting Temperature (V1 p. 240) (the temperature at which the snow starts to melt - usually 0 C). If the air temperature is above the threshold, then the snow will melt at the rate specified by the Degree-day Melting or Freezing Coefficient (V1 p. 241).
Dry snow acts like a sponge and does not immediately release melting snow. Thus, melting snow is added to wet snow storage. When the amount of wet snow exceeds the Maximum Wet Snow Fraction in Snow Storage (V1 p. 243), the excess is added to ponded water, which is then free to infiltrate or runoff.
More detailed information on the snow melt process can be found in the on-line help for the individual dialogues and in the Snow Melt - Technical Reference (V1 p. 449) section.
For snow melt, the air temperature is critical. However, the air temperature changes significantly with elevation. In areas with significant elevation changes, snow will accumulate in upland areas - often were there is limited weather data available. The elevation correction for air temperature allows you to specify an elevation for the temperature stations and a temperature change rate with elevation. During the pre-processing, a temperature change factor is calculated for each cell and the actual temperature in the cell is calculated during the simulation using this factor.
In terms of snow melt, the air temperature along with the degree day melting coefficient determine the amount of melting that can occur. If you have daily temperature data it may be difficult to properly account for the diurnal melting and freezing cycles.
Air temperature can also be an important parameter during water quality simulations.
For more information on the snow melt parameters, see the specific snow melt dialogue information in the Climate (V1 p. 229) section of the on-line help and User Interface manual
Frozen Ground
Frozen ground is not directly simulated in MIKE SHE, but can be approximated by using a time varying infiltration rate, where you manually reduce the infiltration rate during the winter. More information on this can be found in the section, Time varying surface infiltration (frozen soils) (V1 p. 742).