Geoscience Reference
In-Depth Information
Q
E
700
700
Q
*
Oasis
Desert
Oasis
Desert
Q
*
Q
H
350
350
Q
G
Q
G
0
0
8
12
16
20
24
12
24
Hours
Q
H
Figure 8.4
Net radiation on the left and energy budget on the right for an oasis and a desert site. Q
H
sensible heat flux, Q
E
latent
heat flux, Q
G
is soil heat flux. In the oasis Q
E
is sustained by Q
H
from the warmer atmosphere and can become similar to the net
radiation value.
plants increases, so does the degree of microclimatic
modification.
Let us look at some of the detailed effects of plants on
the microclimate by considering conditions around a
single leaf. The amount of short-wave radiation absorbed
by a leaf depends upon the quantity of radiation reaching
its upper surface, the angle between the leaf and the sun's
rays, and the colour of the leaf. Through absorption, the
temperature of the leaf rises and, consequently, the
amount of long-wave radiation emitted also increases.
Some radiation is transferred downwards towards the
soil, and some flows upwards. With a large number of
leaves the sun's rays are increasingly obstructed, so the
Microclimate above a vegetated surface
The nature of microclimatic conditions and processes
becomes far more complex when vegetation cover is
present, for not all the energy is absorbed at a single
surface. Some is absorbed by the top of the vegetation,
some penetrates into the plants, and some may even reach
the soil surface. The amount that gets through to the soil
depends upon the height of the crop, the density of the
leaves and the angle of the sun's rays. As the size of the
Height above
Hour of day
surface (m)
1
5
7
9
11
13
15
17
19
21
Irrigated oasis
2
21·4
18·9
20·7
25·4
30·5
33·2
33·9
33·7
30·0
26·4
25
23·8
20·8
21·8
25·3
30·2
33·0
33·9
34·3
30·9
29·7
50
26·2
22·6
22·5
25·5
30·0
33·1
33·5
34·5
31·6
32·7
100
28·6
25·9
23·8
25·9
29·9
33·0
33·3
34·0
31·9
34·2
Semi-desert
2
23·0
19·9
23·1
28·4
33·5
37·0
36·7
37·8
33·9
29·4
25
24·5
21·4
23·5
28·1
33·4
35·6
35·3
36·5
33·5
32·2
50
26·2
22·6
23·9
28·2
33·4
35·0
34·7
36·3
33·0
32·9
100
28·6
23·9
25·1
27·8
32·9
34·6
33·9
35·8
32·8
33·1
Source: After Goltsberg (1969).
