pbsmSnobal (Pomeroy and Li, 1999)
Defined in Classpbsm. This module calculates snow transport and sublimation. The snowfall observation can be a daily total or the actual interval snowfall. The former case is handled by assuming that the snowfall is uniformly distributed over every interval of the day. The transport and sublimation of blowing snow are calculated every interval using the interval wind speed, air temperature and relative humidity. The model has been extended to handle the transport of snow between HRUs. At the end of a day when snow transport has occurred, snow transported from HRUs with low roughness is distributed over the HRUs with greater roughness according to the fractions specified in the distribution parameter. No transported snow enters the HRU with the lowest roughness. When HRUs with lower vegetative height fill to their maximum, the excess is distributed over the remaining unfilled HRUs. This is a modification of the original PBSM. SWE is now a state variable of Snobal accessed by pbsmSnobal using a PUT.
Observations
- none
Variables
- hru_subl (mm Dt) - the mass of snow lost from an HRU by sublimation in time step, Dt – expressed as an equivalent average depth of water over an HRU.
- cumSubl (mm) - cumulative sublimation.
- hru_drift (mm Dt) - the mass of snow lost from an HRU by snow transport in time step, Dt – expressed as an equivalent average depth of water over an HRU.
- Drift_out (mm Dt) - the mass of snow lost from an HRU by snow transport in time step, Dt – expressed as an equivalent
- Drift_in (mm Dt) - the mass of snow gained from an HRU by snow transport in time step, Dt – expressed as an equivalent
- cumDrift (mm) - cumulative transport.
- cumSno (mm) - snow (net_snow) accumulation from beginning of winter.
- Prob () - interval probability of blowing snow.
- BasinSnowLoss (mm Dt) - transport out of basin.
- cumBasinSnowLoss (mm) - cumulative transport out of basin.
- cumBasinSnowGain (mm) - cumulative transport into basin.
- snowdepth (m) - calculated snow depth from SWE (Gray/Pomeroy).
Parameters
- fetch (m) - fetch distance.
- Ht (m) - crop height.
- distrib () - distribution fractions. Value for HRU 1 controls snow transport into the basin.
- N_S (1/m^2) - vegetation number density.
- A_S (m) - stalk diameter or silhouette.
- basin_area (km2) - basin area.
- hru_area (km2) - hru_area.
- inhibit_evap (flag) - an output parameter set true when the SWE is greater than zero. It is used to inhibit evaporation from the evaporation modules.
- inhibit_bs (flag) - an input inhibiting blowing snow when set equal to 1. Inhibited HRU is still able to receive drift from other HRUs.
Variable Inputs
- hru_t (°C) - air temperature from module obs.
- hru_ea (kPa) - vapour pressure from module obs.
- hru_u (m/s) - wind speed from module obs.
- net_snow (mm Dt) - snow fall from wild module - intcp, brushintcp etc.
- SWE (mm) - snow water equivalent. Put.
- z_s (m) - snowcover depth. Put.
- rho (kg/m^3) - snow density. Put.
Notes
- The parameter fetch cannot be less than 300m.
- The parameter distrib for the first HRU is used differently from all the other HRUs. It determines the drift into the model basin based upon the drift out of the first HRU. BasinSnowGain is equal to distrib[HRU1]*Drift[HRU1].
- The first HRU, i.e. the lowest vegetation height. When the snow is redistributed, the distrib values for the HRU's not filled to their vegetation height are summed and each HRU receives its share. The sum of distributions need not add to 1.0.
E.g. if the transport D is redistributed over HRUs: A, B and C with their distrib parameter having values of a, b and c respectively. The snow transport would be distributed as:
a*D/(a + b +c), b*D/(a + b +c) and c*D/(a + b +c). Note that any excess from a HRU filling to its vegetation height is deposited in the last HRU, i.e. the one having the tallest vegetation.
3. If the value of distrib is less than 0 for an HRU, all snow transport to its capacity is assumed to be caught by this HRU. The next HRU is the beginning of a new blowing snow regime
4. Cumulative drift from the last HRU is handled as follows:
distrib > 0.0 - the drift is handled as described above. Any excess after the vegetation is full is transported out of the basin - i.e. added to 'BasinSnowLoss'.
distrib < 0.0 - all drift is deposited in the hru.
distrib == 0.0 - all driftt is transported out of the basin - i.e. added to 'BasinSnowLoss'.