Geoscience Reference
In-Depth Information
Canopy evaporation
E
int, c
Tr unk evaporation
E
int, t
Gross rainfall
P
Canopy input
(1-r-r
t
)
P
Free throughfall
r
P
Tr unk input
r
t
P
E
int, C
=
E
pot
if C
≥
S
E
int, t
=
ε
E
pot
if C
t
≥
S
t
if C
t
<
S
t
C
S
C
t
S
t
E
int, C
=
E
pot
if C
<
S
E
int, t
=
ε
E
pot
C
S
C
t
S
t
Canopy drainage
D
=
D
s
exp[b (C - S)]
l
s
=
C
t
-
S
t
l
s
=
0
if C
t
≥
S
t
if C
t
<
S
t
Throughfall
l
t
Stemflow
l
s
Figure 6.26
Scheme of the Rutter model (Rutter et al.,
1975
).
where
ε
is a constant describing the evaporation rate from saturated trunks as a pro-
portion of that from the saturated canopy. Stemlow
I
s
for a given time step is calcu-
lated with the following equation:
ICS
=−
if
if
C
≥
S
s
t
t
t
t
(6.46)
I
=
0
C
<
S
s
t
t
The model requires rainfall intensities at short time intervals, for example, every 10
minutes. Proper simulation of the canopy and trunk storage amounts requires a suit-
able numerical integration method or analytical integration of the model equations
(Lloyd et al.,
1988
). The model has been developed for relatively closed canopies,
particularly for the evaporative process, through the assumption that the canopy and
trunk storages extend to the whole plot area. Valente et al. (
1997
) adapted the Rutter
model for sparse forests.
Gash (
1979
,
1995
) simpliied the Rutter model and put forward a well-known ana-
lytical interception model. His model represents rainfall input as a series of discrete
storms that are separated by intervals long enough for the canopy and stems to dry
completely - this assumption is possible by the rapid drying of forest canopies. Each
individual storm is then divided into three subsequent phases: canopy wetting-up,
saturation and drying. For the irst two of these phases, the actual rates of evapora-
tion and rainfall are replaced by their mean rates for the entire period being modelled
(Muzylo et al.,
2009
).
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