Geoscience Reference
In-Depth Information
Figure 21.7
The whole canopy
single source model used to
derive the whole canopy version
of the Penman-Monteith
equation.
universally used in hydrological and meteorological modeling, sometimes, but not
always, with the inclusion of below canopy fluxes from the soil, which may also be
calculated using the Penman-Monteith Equation applied at the soil surface.
If below canopy fluxes are neglected (they can be small below a fully developed
vegetation canopy), the representation of whole-canopy surface energy balance in
the big leaf representation can be calculated by a whole-canopy version of the
Penman-Monteith Equation. In this case (see Fig. 21.7) the equations representing
the whole-canopy exchanges of sensible heat,
H
, and latent heat flux,
λ
E
, are
respectively:
(
TT
−
)
s
ref
(21.30)
Hc
=
r
ap
H
r
a
and:
r
(() )
ap sat s f
H
ceT e
−
(21.31)
E
l
=
g
r
+
a
s
where
T
ref
and
e
ref
are the temperature and vapor pressure at a reference level above
the canopy,
T
s
is the canopy-average leaf surface temperature,
r
s
is the canopy-
average leaf stomatal resistance (often called the 'surface resistance'), and
r
a
H
and
r
a
V
are the aerodynamic resistances for the transfer of water vapor and sensible
heat (which include
both
the canopy-average leaf boundary-layer resistances and
the aerodynamic transfer resistance for turbulent transport between the effective
