Geoscience Reference
In-Depth Information
30
25
20
15
10
5
0
5
potential
E
actual
E
4
3
2
1
0
10
8
6
4
2
0
0
90
180
270
360
Time (day of year)
Figure 1.2
Daily rainfall luxes (top) and simulated daily evapotranspiration (mid-
dle) and drainage luxes (bottom) of grass on a sandy soil in a Dutch climate and
with a deep groundwater table. Potential evapotranspiration in the middle panel is
the evapotranspiration that would occur if suficient water would have been available
to the plants.
1.2 Conservation of Energy and Mass
To study the processes at Earth's surface in a quantitative way we irst need to deine
that interface clearly. This is done with the help of a control volume that contains the
interface. Any difference between the inlow and outlow of a quantity will result in a
change in the storage in the control volume. Formally, the conservation equation for
an arbitrary quantity can be stated as:
∑∑
∆
F
−
F
=
S
(1.1)
in
out
where Σ
F
in
and Σ
F
out
are the summation of all luxes into and out of the control vol-
ume, respectively, and ∆
S
is the change in storage (see
Figure 1.3
). To capture all
important processes we start with a control volume that contains (part of) the soil
column, as well as the part of the atmosphere into which the vegetation protrudes. In
the horizontal direction the control volume has an arbitrary size, but horizontal homo-
geneity is assumed.
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