Interception capacity with snow interception

If snow interception is included in the simulation, the interception capacity, S_imax, can be calculated in two different ways, either as a function of thermal quality or as a function of air temperature (see switch SnowIntUnload). In the latter case interception capacity is calculated as:

                       (3.56)

where i_LAIsnow, i_LAI and i_base are parameters, and A_l is the leaf area index. In this case, thermal quality Q_I^* is assumed to be equal to the thermal quality of precipitation, Q_P calculated in eq.(4.36).

When the interception capacity is a function of thermal quality, it is instead calculated as:

                                (3.57)

Q_I^* is the thermal quality (fraction of frozen water) of the intercepted water and can either be calculated as a weighted sum of the thermal quality of the intercepted water from the previous time-step, Q_I, and the thermal quality of new precipitation. Thermal quality is calculated as:

                                          (3.58)

where Q_P is the thermal quality of precipitation calculated in eq.(4.36). f_new is the fraction of new intercepted precipitation in relation to total intercepted storage:

                                                             (3.59)

where P is precipitation and S_i is the interception storage.

When the interception storage, S_i, has been calculated in each time-step, a new value on thermal quality of intercepted water, Q_I, is calculated:

                                                       (3.60)

where Q_I^* is the thermal quality of intercepted water calculated in the beginning of the time-step and S_i is the interception storage. The amount of melted intercepted storage, S_melt, is estimated by:

                                               (3.61)

where i_scale is a parameter and M(S_snowthick) is the function for calculating snow melt, eq.(4.32)-(4.34). S_snowthick replaces Δz_snow and is calculated as:

                            (3.62)

where S_int is the interception storage, ρ_water is the density of water, Q_I^* is the thermal quality of intercepted water calculated in the beginning of the time-step and A_l is the leaf area index. The figure 100 in the equation is an approximation of the snow density.