Agriculture Reference
In-Depth Information
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long-term mean values, especially in 1984, and only slightly recovered to
near their long-term average values in 1985. This deficit is a reflection of
the large-scale rainfall deficit that affected the entire Sahelian region and
extended into East Africa. The NDVI declined by 10-40% of normal NDVI
during the period from the end of 1983 to the end of 1984 only slightly
recovering to near normal in 1985. This indicates that the persistence of
earlier drought conditions may have dampened the expected improvement
in vegetation conditions with the return of near-normal rainfall conditions
in 1985.
The NDVI patterns in 1996 to mid-1997 were associated with drought
conditions that prevailed over most of East Africa during this period. NDVI
declined by 20% for most of 1996 and early 1997 but was above normal
for the period from late 1997 through 1998.
The drought of 1984 caused significant reduction in maize production
(figure 5.9c). In 1984, only 1.4 million tons of maize was produced, com-
pared to 3.0 million tons in 1994 and 2.4 million tons in 1998. Periods
of reduced maize production (1984, 1992, 1996, 2000) corresponded to
the occurrence of El Ni no/Southern Oscillation (ENSO) cold events (which
typically resulted in below-normal rainfall) and below-normal NDVI val-
ues (figures 5.9a,b).
The spatial anomaly patterns of drought conditions during March—
May (critical growing period) 1984 are shown in figure 5.10. The drought
pattern in 1984 was most pronounced in Kenya, especially the eastern part,
and most of Ethiopia and Somalia. A large part of East Africa had NDVI
values that were 10-60% below normal. Monthly NDVI in 1992 was well
below normal (figure 5.11a). Figure 5.11b shows the interannual variability
in maize production for Zimbabwe from 1981 to 2000.
[71],
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So
uthern Africa
In southern Africa, the worst drought of the century occurred during 1991-
1992 and affected nearly 100 million people. The most affected countries
were Zimbabwe and Botswana.
The years 1983, 1987, 1992, 1995, and 1998 showed large deficits in
production, with the lowest production in 1992 (figure 5.11b). All of these
years represented periods of ENSO warm events, which were associated
with below-normal rainfall and the prevalence of drought conditions over
most of the region (Cane et al., 1994; Phillips et al., 1998). Drought years
also led to inadequate forage and poor nutrition for animals, resulting in
reduced carcass weight and increased cattle mortality (figure 5.12).
Unlike East Africa, southern Africa has only one growing season that
normally begins in November and ends in April. Figure 5.11a shows the
temporal evolution of monthly NDVI values and the respective long-term
means for Zimbabwe for 1991-93. The time series data showed a uni-
modal pattern, with the NDVI reaching a maximum of about 0.4 units
in February—March after the maximum rainfall in December—January.
The dry season typically includes the period from late May to October,
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