equilibrium.imposed.ET {bigleaf} | R Documentation |

Evapotranspiration (ET) split up into imposed ET and equilibrium ET.

```
equilibrium.imposed.ET(
data,
Tair = "Tair",
pressure = "pressure",
VPD = "VPD",
Gs = "Gs_ms",
Rn = "Rn",
G = NULL,
S = NULL,
missing.G.as.NA = FALSE,
missing.S.as.NA = FALSE,
Esat.formula = c("Sonntag_1990", "Alduchov_1996", "Allen_1998"),
constants = bigleaf.constants()
)
```

`data` |
Data.frame or matrix containing all required input variables |

`Tair` |
Air temperature (deg C) |

`pressure` |
Atmospheric pressure (kPa) |

`VPD` |
Air vapor pressure deficit (kPa) |

`Gs` |
surface conductance to water vapor (m s-1) |

`Rn` |
Net radiation (W m-2) |

`G` |
Ground heat flux (W m-2); optional |

`S` |
Sum of all storage fluxes (W m-2); optional |

`missing.G.as.NA` |
if |

`missing.S.as.NA` |
if |

`Esat.formula` |
Optional: formula to be used for the calculation of esat and the slope of esat.
One of |

`constants` |
cp - specific heat of air for constant pressure (J K-1 kg-1) |

Total evapotranspiration can be written in the form (Jarvis & McNaughton 1986):

`ET = \Omega ET_eq + (1 - \Omega)ET_imp`

where `\Omega`

is the decoupling coefficient as calculated from
`decoupling`

. `ET_eq`

is the equilibrium evapotranspiration rate,
the ET rate that would occur under uncoupled conditions, where the heat budget
is dominated by radiation (when Ga -> 0):

`ET_eq = (\Delta * (Rn - G - S) * \lambda) / (\Delta + \gamma)`

where `\Delta`

is the slope of the saturation vapor pressure curve (kPa K-1),
`\lambda`

is the latent heat of vaporization (J kg-1), and `\gamma`

is the psychrometric constant (kPa K-1).
`ET_imp`

is the imposed evapotranspiration rate, the ET rate
that would occur under fully coupled conditions (when Ga -> inf):

`ET_imp = (\rho * cp * VPD * Gs * \lambda) / \gamma`

where `\rho`

is the air density (kg m-3).

A data.frame with the following columns:

`ET_eq` |
Equilibrium ET (kg m-2 s-1) |

`ET_imp` |
Imposed ET (kg m-2 s-1) |

`LE_eq` |
Equilibrium LE (W m-2) |

`LE_imp` |
Imposed LE (W m-2) |

Surface conductance (Gs) can be calculated with `surface.conductance`

.
Aerodynamic conductance (Ga) can be calculated using `aerodynamic.conductance`

.

Jarvis, P.G., McNaughton, K.G., 1986: Stomatal control of transpiration: scaling up from leaf to region. Advances in Ecological Research 15, 1-49.

Monteith, J.L., Unsworth, M.H., 2008: Principles of Environmental Physics. 3rd edition. Academic Press, London.

```
df <- data.frame(Tair=20,pressure=100,VPD=seq(0.5,4,0.5),
Gs_ms=seq(0.01,0.002,length.out=8),Rn=seq(50,400,50))
equilibrium.imposed.ET(df)
```

[Package *bigleaf* version 0.8.2 Index]