Geoscience Reference
In-Depth Information
4.0
Gash
with:
r
= 0.32 (-)
r
t
= 0.02 (-)
S
= 0.8 mm
P
mean
= 1.38 mm h
-1
E
mean
= 0.19 mm h
-1
P
s
= 1.359 mm
3.0
2.0
Von Hoyningen-Hüne and Braden
with:
a
= 0.25 mm
SC
= 1.00 (-)
LAI
= 4.00 (-)
Forests
Maximum =
a LAI
1.0
Agricultural crops
0.0
P
s
0
5
10
15
20
Precipitation
P
(mm)
Figure 6.27
Interception as function of precipitation according to Gash (
1979
) and
Hoyningen-Hüne (
1983
) and Braden (
1985
).
interception in agricultural crops. They proposed the following simple formula for
canopy interception:
1
1
−
SC
LAI
P
(6.51)
Pa
=
LAI
1
+
i
a
where LAI is leaf area index (leaf m
2
soil m
-2
),
a
is an empirical coeficient (m d
-1
)
and SC represents the soil cover fraction (-). For increasing amounts of precipitation,
the amount of intercepted precipitation asymptotically reaches the saturation amount
a
LAI (
Figure 6.27
). In principle
a
must be determined experimentally, but a common
value for ordinary agricultural crops is 0.25 mm d
-1
. Equation (
6.51
) is based on daily
precipitation values and yields daily interception amounts.
6.8 Summary
Water plays a key role in many plant physiological processes. As plants rely on the
water available at their local spot, a proper analysis of root water uptake as affected
by climate, soil texture, plant type and drainage condition forms the basis for many
environmental studies. Also a close relation appears to exists among root water
uptake, plant transpiration and vegetation growth. For analysis of root water uptake
we described a physically based microscopic approach and a more empirical macro-
scopic approach. We discuss the hydraulic head decline in the soil-plant-atmosphere
Search WWH ::
Custom Search