PENMON: Evapotranspiration
In VEZY/DynACof: A Process-Based Model to Study Growth, Yield and Ecosystem Services of Coffee Agroforestry Systems

Description Usage Arguments Details Value Note References See Also Examples

Compute the daily evaporation or transpiration of the surface using the Penman-Monteith equation.

PENMON(
  Rn,
  Wind,
  Tair,
  ZHT,
  Z_top,
  Pressure,
  Gs,
  VPD,
  LAI,
  extwind = 0,
  wleaf = 0.068,
  Parameters = Constants()
)

`Rn`	Net radiation (MJ m-2 d-1)
`Wind`	Wind speed (m s-1)
`Tair`	Air temperature (Celsius degree)
`ZHT`	Wind measurement height (m)
`Z_top`	Canopy top height (m)
`Pressure`	Atmospheric pressure (hPa)
`Gs`	Stomatal conductance (mol m-2 s-1)
`VPD`	Vapor pressure deficit (kPa)
`LAI`	Leaf area index of the upper layer (m2 leaf m-2 soil)
`extwind`	Extinction coefficient. Default: `0`, no extinction.
`wleaf`	Average leaf width (m)
`Parameters`	Constant parameters, default to `Constants()`, if different values are needed: Cp specific heat of air for constant pressure (J K-1 kg-1) Rgas universal gas constant (J mol-1 K-1) Kelvin conversion degree Celsius to Kelvin H2OMW conversion from kg to mol for H2O (kg mol-1) GBVGBH conversion from water conductance to heat conductance

The daily evapotranspiration is computed using the Penman-Monteith equation, and a set of conductances as :

ET= (Delta * Rn*10^6 + rho * Cp * (VPD/10) * GH) / (Delta + gamma * (1 + GH / GV))/λ

where Δ is the slope of the saturation vapor pressure curve (kPa K-1), ρ is the air density (kg m-3), GH the canopy boundary layer conductance (m s-1), γ the psychrometric constant (kPa K-1) and GV the boundary + stomatal conductance to water vapour (m s-1). To simulate evaporation, the input stomatal conductance Gs can be set to nearly infinite (e.g. Gs= 1\cdot e^9).

ET, the daily (evapo|transpi)ration (mm d-1)

If wind=0, it is replaced by a low value of 0.01

Allen R.G., Pereira L.S., Raes D., Smith M., 1998: Crop evapotranspiration - Guidelines for computing crop water requirements - FAO Irrigation and drainage paper 56.

bigleaf::potential.ET() and MAESPA model

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# leaf evaporation of a forest :
PENMON(Rn= 12, Wind= 0.5, Tair= 16, ZHT= 26, Z_top= 25, Pressure= 900, Gs = 1E09, VPD= 2.41,
       LAI=3, extwind= 0.58, wleaf=0.068)