Environmental Engineering Reference
In-Depth Information
1965
1974
1989 1998
28.0
27.5
y = 0.1079 x + 26.407
27.0
26.5
y = 0.0394 x + 26.093
26.0
25.5
25.0
1
2
3
4
5
6
7
8
9
10
Number of years
Source: Meteorological Services Dept, Accra
Figure 4.5 Annual mean temperature at Koforidua (1965-1974 and 1989-1998)
and potential evapotranspiration (PET). Although not representative of the entire
southern Ghana demonstration site, the water balance makes it possible for one
to establish fairly accurately the degree to which water requirements for general
plant growth are satisfied in a given place. Crop possibilities can only be determined
when the moisture requirements of individual crops are known (Benneh, 1971).
Comparing the mean water balance at Koforidua over the two periods, it is
observed that there is now a distinct break between the major and minor planting
seasons, and a higher PET for the 1990s. This is indicative of increasing water
deficit and decreasing soil moisture availability for plant growth in the minor season
farming because most crops have “moisture-sensitive periods” during which a
water deficit could reduce the economic yields much more than at other periods.
The farmers who were interviewed generally saw a lot of evidence of climatic
change. They observed a change in the natural vegetation and in the relative
importance of some trees, for example the gradual disappearance of timber
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