4.5. Actual Evapotranspiration¶

ADELM diagnoses total actual evapotranspiration and converts the individual mass-based fluxes to a latent heat flux.

Coupling to other components

Canopy Hydrology provides canopy_evaporation_mmday and canopy_solid_sublimation_mmday.
Snow Hydrology provides snow_sublimation_mmday.
Soil Hydrology provides soil_evaporation_mmday and transpiration_mmday.
Atmospheric Thermodynamics provides latent_heat_of_vaporization.

1. Total evapotranspiration¶

Total actual evapotranspiration total_et_mmday [mm day-1; Flux: total evapotranspiration water flux to the atmosphere] is the sum of all five actual water-vapour fluxes:

(4.5.1)¶\[ET = E_{\mathrm{snow}} + E_{\mathrm{sub}} + E_{\mathrm{can,liq}} + E_{\mathrm{soil}} + E_{\mathrm{tr}}\]

where \(E_{\mathrm{snow}}\) is snow_sublimation_mmday [mm day-1; Flux: water flux sublimated from the ground snowpack], \(E_{\mathrm{sub}}\) is canopy_solid_sublimation_mmday [mm day-1; Flux: water flux sublimated from snow intercepted on the canopy], \(E_{\mathrm{can,liq}}\) is canopy_liquid_evaporation_mmday [mm day-1; Flux: water flux evaporated from wet canopy surfaces], \(E_{\mathrm{soil}}\) is soil_evaporation_mmday [mm day-1; Flux: water flux evaporated from the top soil layer], and \(E_{\mathrm{tr}}\) is canopy_transpiration_mmday [mm day-1; Flux: water flux from the soil column to the atmosphere through plants].

2. Latent heat flux¶

The latent heat flux latent_heat_flux_Wm2 [W m-2; Flux: latent heat flux associated with evaporation and sublimation] converts mass-based ET fluxes to an energy flux. Liquid-phase and solid-phase fluxes use different latent heats:

(4.5.2)¶\[LE = \frac{ \lambda_{\mathrm{v}}\left(E_{\mathrm{can,liq}} + E_{\mathrm{soil}} + E_{\mathrm{tr}}\right) + \lambda_{\mathrm{s}}\left(E_{\mathrm{snow}} + E_{\mathrm{sub}}\right) }{\Delta t_{\mathrm{day}}}\]

where \(\lambda_{\mathrm{v}}\) is latent_heat_of_vaporization [J kg-1; Diagnostic: energy required to vaporize one kilogram of liquid water], \(\lambda_{\mathrm{s}}\) is latent_heat_of_sublimation [default: 2.836e+06 J kg-1; Constant: latent heat of sublimation of water at 0°C], and \(\Delta t_{\mathrm{day}}\) is seconds_per_day [default: 86400 s; Constant: number of seconds in one day]. The denominator converts mm day⁻¹ to kg m⁻² s⁻¹ (equivalently W m⁻²), using a water density of 1000 kg m⁻³.