Canopy#

Canopy storage and related fluxes are calculated based on section 4.2 of Müller Schmied et al 2021 [1].

canopy.canopy_water_balance(canopy_storage, daily_leaf_area_index, potential_evap, precipitation, current_landarea_frac, landareafrac_ratio, max_storage_coefficient, minstorage_volume, x, y)[source]#

Calulate daily canopy balance including canopy storage and water flows entering and leaving the canopy storage.

Parameters:
canopy_storagefloat

Daily canopy storage, Units: [mm]

daily_leaf_area_indexfloat

Daily leaf area index Units: [-]

potential_evapfloat

Daily potential evapotranspiration, Units: [mm/day]

precipitationfloat

Daily precipitation, Units: [mm/day]

current_landarea_fracfloat

Land area fraction of current time step, Units: [-]

landareafrac_ratiofloat

Ratio of land area fraction of previous to current time step, Units: [-]

max_storage_coefficient:

coefficient for computing maximum canopy storage, Units: [-]

minstorage_volume: float

Volumes at which storage is set to zero, units: [km3]

Returns:
canopy_storagefloat

Updated daily canopy storage, Units: [mm]

throughfallfloat

Throughfall, Units: [mm/day]

canopy_evapfloat

Canopy evaporation, Units: [mm/day]

pet_to_soilfloat

Remaining energy for addtional soil evaporation, Units: [mm/day]

land_storage_change_sumfloat

Sum of change in vertical balance storages, Units: [mm]

daily_storage_transferfloat

Storage to be transfered to runoff when land area fraction of current time step is zero, Units: [mm]

Water balance#

The canopy storage \(S_c\) \([mm]\) is calculated as:

\[\frac{dS_c}{d_t} = P − P_t − E_c\]

where \(P\) is precipitation \([mm/d]\), \({P}_{t}\) is throughfall, the fraction of \(P\) that reaches the soil \([mm/d]\) and \({E}_{c}\) is evaporation from the canopy \([mm/d]\).

Note

Canopy storage is also a function of land area fraction.

Inflows#

Daily precipitation \(P\) is read in from the selected climate forcing (see Climate Forcing in Data section).

Outflows#

Throughfall \(P_t\) is calculated as

\[ P_t= \begin{cases} 0, & \text{if } P<({S_c}_{,max}- S_c) \\ P - ({S_c}_{,max} - S_c), & \text{otherwise} \end{cases} \]

where \({S_c}_{,max}\) is the maximum canopy storage calculated as:

\[{S_c}_{,max} = m_c \times L\]

where \(m_c\) is 0.3 mm [2], and \(L [-]\) is the oneside leaf area index. \(L\) is a function of daily temperature and precipitation and is limited to minimum or maximum values. Maximum \(L\) values per land cover class (Table C1 in Müller Schmied et al. 2021) [1], whereas minimum \(L\) values are calculated as:

\[{L}_{min} = 0.1{f_d}_{,lc} + (1 − {f_d}_{,lc}){c_e}_{,lc}{L}_{max}\]

where \({f_d}_{,lc}\) is the fraction of deciduous plants and \({c_e}_{,lc}\) is the reduction factor for evergreen plants per land cover type (Table C1) [1]. See Lead Area Index section under API reference for leaf Area index calculation.

Canopy evaporation \(E_c\) following Deardorff (1978) [2], is calculated as:

\[E_c = {E}_{pot}\Big(\frac{S_c}{{S_c}_{,max}}\Big)^\frac{2}{3}\]

where \({S_c}\) \([mm]\) is the canopy storage, calculated in canopy storage under Outflows and \({S_c}_{,max}\) \([mm]\) is the maximum canopy storage.

See Radiation and Evapotranspiration section for potential evaporation calculation.

References#