Gb_h: Leaf boundary layer conductance for heat

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

Description

Compute the bulk leaf boundary layer conductance for heat using the wind speed, the leaf dimension, and leaf area distribution following Jones (1992) or Leuning et al. (1995).

Usage

Gb_h(
  Wind,
  wleaf = 0.068,
  LAI_lay,
  LAI_abv,
  extwind = 0,
  Z_top,
  ZHT,
  Z0 = Z_top * 0.1,
  ZPD = Z_top * 0.75,
  alpha = 1.5,
  ZW = ZPD + alpha * (Z_top - ZPD),
  Tleaf = NULL,
  Tair = NULL,
  Dheat = Constants()$Dheat,
  formulation = c("Jones_1992", "Leuning_1995")
)

Arguments

Wind	Average daily wind speed above canopy (m s-1)
wleaf	Average leaf width (m)
LAI_lay	Leaf area index of the layer (m2 leaves m-2 soil)
LAI_abv	Cumulated leaf area index above the layer (m2 leaves m-2 soil)
extwind	Extinction coefficient. Default: 0, no extinction.
Z_top	Average canopy height of the taller crop (m)
ZHT	Wind measurement height (m)
Z0	Roughness length (m). Default: 0.1*Z_top
ZPD	Zero-plane displacement (m), Default: 0.75*Z_top
alpha	Constant for diffusivity at top canopy. Default: 1.5 following Van de Griend et al (1989).
ZW	Top height of the roughness sublayer (m). Default: ZPD+alpha*(Z_top-ZPD)
Tleaf	Leaf temperature (deg C). Only needed if formulation="Leuning_1995"
Tair	Canopy air temperature (deg C). Only needed if formulation="Leuning_1995"
Dheat	Molecular diffusivity for heat (m2 s-1). Default to Constants()$Dheat. Only needed if formulation="Leuning_1995"
formulation	The formulation used to compute Gb_h

Details

The leaf boundary layer conductance for heat can be transformed into leaf boundary layer conductance for water vapour as follow:

Gb_w= 1.075*gb_h

Note that Gb_w should be doubled for amphistomatous plants (stomata on both sides of the leaves).

Value

Gb	The leaf boundary layer conductance for heat (m s-1)

References

• Leuning, R., et al., Leaf nitrogen, photosynthesis, conductance and transpiration: scaling from leaves to canopies. Plant, Cell & Environment, 1995. 18(10): p. 1183-1200.

• Mahat, V., D.G. Tarboton, and N.P. Molotch, Testing above‐ and below‐canopy represetations of turbulent fluxes in an energy balance snowmelt model. Water Resources Research, 2013. 49(2): p. 1107-1122.

See Also

G_bulk(), G_soilcan(), G_interlay() and GetWind(), which is used internaly.

Examples

# Gb for a coffee plantation managed in agroforestry system:
Gb_h(Wind=3,wleaf=0.068,LAI_lay=4,LAI_abv=0.5,ZHT=25,Z_top=24,extwind=0.58)

VEZY/DynACof documentation built on Feb. 3, 2021, 8:52 p.m.