Environmental Engineering Reference
In-Depth Information
the best results are achieved when the farmers
can see clear and immediate rewards in addition
to the less obvious longer-term environmental
benefits (Pégorié 1990). On the human side,
population growth rates and densities must be
examined with a view to assessing human
pressure on the land. Over-population has
traditionally been regarded as an integral part of
the drought/famine/ desertification relationship,
but that too has been re-examined. Mortimore
(1989), for example, has suggested that high
population densities may not be out of place in
areas where proposed soil and water conservation
schemes are labour intensive. Ironically, some
areas suffer from rural depopulation. In the early
1980s, urban populations across Africa increased
at about 6 per cent per year, due in large part to
the exodus from rural areas (Grove 1986). Where
relief from population pressure is needed, it may
come in the form of family planning or through
relocation. Despite potentially serious social and
political concerns, these may be the only ways
to tackle the population problem (Mackenzie
1987b).
The fight against desertification has been
marked by a distinct lack of success. Recent
reassessments of the problem, beginning in the
late 1980s, suggest that this may be the result of
the misinterpretation of the evidence and a
poor understanding of the mechanisms that
cause and sustain the degradation of the land.
The additional research required to resolve that
situation will further slow direct action against
desertification, but it may be the price that has
to be paid to ensure future success.
essentially socio-economic elements, but the
first is physical and it has led to numerous
attempts by climatologists in recent years to
devise a method by which drought may be
predicted.
Drought is not the sole cause of famine or
desertification, but it is certainly a major cause,
often initiating the problem only to have it
intensified by other factors. Prevention of
drought is not feasible at present, nor would it
necessarily bring about an end to famine and
desertification if it was. If drought could be
predicted, however, responses could be
planned, and the consequences therefore much
reduced. The simplest approach is the actuarial
forecast, which estimates the probability of
future drought based on past occurrences. To
be successful, actuarial forecasting requires a
lengthy sequence of data for analysis
(Schneider 1978). In many areas, including
sub-Saharan Africa, the record is simply too
short to provide a reliable prediction. Problems
with the homogeneity of the meteorological
record may also reduce the significance of the
results.
An extension of the actuarial approach is the
linking of meteorological variables with some
other environmental variable which includes a
recognized periodicity in its behaviour
(Oguntoyinbo 1986). One of the most
commonly cited links of this type is the
relationship between sunspot activity and
precipitation (see Figure 3.13). In North
America, drought on the plains has been
correlated with the minimum of the 22-year
double sunspot cycle. The drought years of the
mid-1970s, for example, coincided with a
period of minimum sunspot activity. The
previous drought, some 20 years earlier, in the
mid-1950s, also fitted into the cycle. Close as
such a correlation may seem, it applies less well
outside the western United States. Furthermore,
the relationship remains a statistical one, and,
as Schneider (1978) has pointed out, there is no
physical theory to explain the connection
between the two phenomena.
In the search for improved techniques of
DROUGHT PREDICTION
Even if all of these methods of dealing with
drought, famine and desertification were to be
initiated immediately, the results would be a
long time coming. In Africa, this means that the
existing and recurring problems of drought and
famine must receive continuing and immediate
attention. To be effective such aid requires an
early warning of the problem, fast response and
timely delivery of relief. The last two are
