Mass balance

The total water content of the snow pack (snow water equivalent), S, is calculated as the sum of the snow water equivalent remaining from the previous time step, S_res, and the total precipitation:

                                                          (4.44)

The partitioning of precipitation into snow and rain is defined by the thermal quality of the precipitation (see Eq. (4.37)):

                                                         (4.45)

The accumulation of free water in the snow pack is calculated as:

                                            (4.46)

where S_wlres is the free water remaining from the previous time step, with the restriction that 0 < S_wl < S, and M is the snow melt. If the free water is above a given retention threshold, S_wlmax, it is released for infiltration into the soil:

                                  (4.47)

such that the remaining amount of free water becomes:

                                                  (4.48)

The retention capacity is assumed to be a fixed fraction, f_ret, of the snow pack water equivalent:

                                                             (4.49)

The snow pack not only contributes melt water to infiltration but soil surface temperature is also influenced through snow depth and thermal conductivity (cf. Eqs. 1.5 and 1.6 in “Soil Heat Processes”).