Snow#
Note
Simulation of the snow dynamics is calculated such that each \(0.5° \times 0.5°\) grid cell is subdivided into 100 non-localized subgrids that are assigned different land surface elevations according to GTOPO30 (U.S. Geological Survey, 1996) [1]. The daily temperature of each subgrid is calculated from the daily temperature at the \(0.5° \times 0.5°\) cell by applying an adiabatic lapse rate of 0.6 \(°C/100m\) [2]. The daily snow water balance is computed for each of the subcells such that within a \(0.5° \times 0.5°\) cell there may be subcells with and without snow cover or snowfall [3]. Subgrid values are then aggregated to \(0.5° \times 0.5°\) cell values. See section 4.3 of Müller Schmied et al 2021 [3].
- snow.snow_water_balance(snow_water_storage, snow_water_storage_subgrid, temperature, precipitation, throughfall, pet_to_soil, land_storage_change_sum, degreeday, current_landarea_frac, landareafrac_ratio, elevation, daily_storage_transfer, adiabatic_lapse_rate, snow_freeze_temp, snow_melt_temp, minstorage_volume, x, y)[source]#
Compute snow water balance for subgrids including snow water storage and water flows entering and leaving the snow storage
- Parameters:
- snow_water_storage :float
Snow water storage, Units: [mm]
- snow_water_storage_subgridarray
Snow water storage divided into 100 subgrids based on GTOPO30 (U.S. Geological Survey, 1996) land surface elevation map, Units: [mm]
- temperature :float
Daily temperature climate forcing, Units: [K]
- precipitation :float
Daily precipitation, Units: [mm/day]
- throughfall :float
Throughfall, Units: [mm/day]
- pet_to_soil :float
Remaining energy for addtional soil evaporation, Units: [mm/day]
- land_storage_change_sum :float
Sum of change in vertical balance storages, Units: [mm]
- degreeday :float
Land cover specific degreeday values based on [1] .Units: [mm/day/C]
- current_landarea_frac :float
Land area fraction of current time step, Units: [-]
- landareafrac_ratio :float
Ratio of land area fraction of previous to current time step, Units: [-]
- elevation :array
and surface elevation map based on GTOPO30 (U.S. Geological Survey, 1996) [1]. Units: [m]
- daily_storage_transfer :float
Storage to be transfered to runoff when land area fraction of current time step is zero, Units: [mm]
- adiabatic_lapse_rate:float
Adiabatic lapse rate , Units: [K/m or °C/m]
- snow_freeze_temp:float
Snow freeze temperature , Units: [K]
- snow_melt_temp:float
Snow melt temperature , Units: [K]
- minstorage_volume: float
Volume at which storage is set to zero, units: [km3]
- x, yLatititude and longitude indexes of grid cells.
- Returns:
- snow_water_storage :float
Updated snow water storage, Units: [mm]
- snow_water_storage_subgrid :array
Updated snow water storage divided into 100 subgrids based on GTOPO30 (U.S. Geological Survey, 1996) land surface elevation map, Units: mm
- snow_fall :float
Snowfall, Units: [mm/day]
- sublimation :float
Sublimation, Units: [mm/day]
- snow_melt :float
Snow melt, Units: [mm/day]
- effective_precipitation :float
Effective Precipitation, Units: [mm/day]
- max_temp_elev :float
Maximum temperature from the 1st(lowest) elevation, Units: [K]
- land_storage_change_sum :float
Sum of change in vertical balance storages, Units: [mm]
- daily_storage_transfer :float
Updated storage to be transfered to runoff when land area fraction of current time step is zero, Units: [mm]
- snowcover_frac: float
Snow cover fraction
- References.
[1] (1,2)U.S. Geological Survey: USGS EROS archive – digital elevation– global 30 arc-second elevation (GTOPO30), available at: https://www.usgs.gov/centers/eros/science/usgs-eros-archivedigital-elevation-global-30-arc-second-elevation-gtopo30?qtscience_center_objects=0#qt-science_center_objects (last access: 25 MArch 2020), 1996
Water balance#
Snow storage \({S}_{sn}\) \([mm]\) is calculated as:
where \({P}_{sn}\) is the part of throughfall \(({P}_{t})\) that falls as snow \([mm/d]\), \(M\) is snowmelt \([mm/d]\) and \({E}_{sn}\) is sublimation \([mm/d]\).
Note
Snow storage is also corrected with land area fraction.
Inflows#
Snow fall from throughfall \({P}_{sn}\) is calculated as:
where \(T\) is daily air temperature \([°C]\), and \({T}_{f}\) is snow freeze temperature, set to \(0 °C\). To prevent excessive snow accumulation, when snow storage \({S}_{sn}\) reaches \(1000 mm\) in a subcell, the temperature in this subcell is increased to the temperature in the highest subcell with a temperature above \({T}_{f}\) [2].
Outflows#
Snow melt \({M}\) is calculated with a land-cover-specific degreeday factor \({D}_{F}\) \([{mmd^−1} {°C^-1})\) (Table C2) [3] when the temperature \(T\) in a subgrid surpasses melting temperature \(T_m = 0 (°C)\) as:
Sublimation \({E}_{sn}\) is calculated as the fraction of \({E}_{pot}\) that remains available after \({E}_{c}\). For calculating \({E}_{pot}\), land-cover-specific albedo values are used if \({S}_{sn}\) surpasses \(3 mm\) in the \(0.5° \times 0.5°\) cell (Table C2) [3]. See potential evapotranspiration under Potential evaporation and canopy evapotranspiration under Canopy evaporation.