Environmental Engineering Reference
In-Depth Information
Table 8.5 Influence of slope orientation on
microclimate
Orientation
After five dry days
After two rain days
Maximum temperature
N
-1·9
-1·5
E
-1·3
0·0
S
2·6
1·4
W
0·5
0·2
Minimum temperature
N
-0·3
-0·4
E
-0·1
-0·4
S
0·4
0·3
W
0·0
0·5
Daily mean temperature
N
-0·9
-0·4
E
0·1
-0·3
S
1·1
0·6
W
-0·4
0·2
Relative humidity at 13.00 (%)
N
8
1
E
3
5
S
-13
-3
W
6
-4
Source
: Translated from Fuh, Baw-Puh (1962).
Note
: Figures are relative to a horizontal surface near by.
SLOPES AT NIGHT
At night, when there is no input of short-wave radiation, the effect of a sloping ground
surface on the energy budget is less pronounced. Figure 8.13 shows the exchanges taking
place. For slopes between 0° and 30°, emission of long-wave radiation follows the cosine
law (
E
sl
=
E
horiz
cos α, where α is the slope angle); at higher angles more radiation is
emitted than would be predicted. The only effect of slope direction is in influencing
surface heating during the day, which, through heat storage, may affect night-time
temperatures and hence emission rates. If the sky is obstructed by trees, other valley
slopes or even buildings, much of the long-wave radiation is absorbed and reradiated
