Snow Melt

The Snow Melt data sub-tree includes all of the specific parameters related to the snow melt module.

Snow melts by converting from dry snow to wet snow. Wet snow is converted to overland flow when the Maximum Wet Snow Fraction in Snow Storage (V1 p. 243) is exceeded.

Include thermal melting - Thermal melting of snow in response to the heat content of rain can be an important factor during spring thaw events, where rain on saturated snow can trigger a significant flood. The rain is assumed to be at the same temperature as the air.

Melting coefficient for thermal energy in rain - The melting coefficient accounts for the energy content or the rain.

(12.6)

where M_rain is the melting rate, C_rain is the melting coefficient due to the energy content of the rain, P is the precipitation rate, T_air is the current air temperature and T₀ is the Threshold Melting Temperature (V1 p. 240).

Factor for reducing the sublimation rate from dry snow -

The ET module will remove water from snow storage before any other ET is removed.

1. ET is removed first from wet snow as evaporation because the energy requirements for evaporation are lower than sublimation. The ET is removed from wet snow at the full rate, assuming that wet snow can be treated the same as ponded water.

2. If there is no wet snow (either because it is too cold or all the wet snow as been evaporated) then ET will be removed from dry snow as sublimation.

However, sublimation has a higher energy requirement than evaporation, so MIKE SHE includes a user defined factor for controlling sublimation. The sublimation factor is a multiplier that reduces the actual ET rate from the snow. If the sublimation factor = 0, then the ET rate is 0. If the sublimation factor = 1.0, then the ET rate is the specified Reference ET rate. Thus,

Maximum ET = (Reference ET) * (Crop Coefficient) * (Sublimation Factor)