Geoscience Reference
In-Depth Information
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Figure 24.4
Schematic
diagram of second
generation one-dimensional
SVATs in which a plot-scale
micrometeorological model
with an explicit vegetation
canopy was applied at grid
scale. See Plate 3 for a colour
version of this image.
Snow pack
Runoff
Runoff
Runoff
Runoff
Deep drainage
Deep drainage
Deep drainage
Deep drainage
Plot-scale, one-dimensional 'micrometeorological' models
Following the use of the Budyko Bucket model, the next generation of SVATS can be
characterized by the developments of Deardorff (1978), who made simplifying
improvements in the representation of soil heat fluxes through the 'force-restore'
scheme, and Dickinson
et al.
(1986) and Sellers
et al.
(1986), who made substantial
improvements in the representation of vegetation controls on evaporation. The
essential essence of this group of SVATS which is illustrated schematically in
Fig. 24.4, is that they were one-dimensional representations of the micrometeoro-
logical interaction of uniform plots of vegetation, but applied at the (much larger)
grid scale used in GCMs.
Notably among the improvements in vegetation-related features was the
introduction of the effect of leaf stomatal resistance through development of the
Monteith (1965) 'big leaf ' assumption and of a canopy water balance to calculate
interception loss using a (usually simplified) version of the Rutter model, both of
which were described in Chapter 22. In this group of SVATS, the temperature of
the vegetation was also sometimes calculated explicitly as a state variable, and dry
canopy surface resistance was usually either assumed constant for a particular
vegetation cover, or parameterized in terms of a series of stress factors in a version
of the Jarvis-Stewart model (see, for example, Shuttleworth, 1989) in which surface
resistance is expressed in the form:
1
(24.1)
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