Monitoring Agricultural Drought in Southern Africa - Monitoring and Predicting Agricultural Drought: A Global Study - page 271

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Line
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-0.1
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Long
PgEn

Fig ure 20.5 Coefficient of variation (%) of Zimbabwe's annual rainfall (1961-2000).

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Associations between southern African interannual rainfall fluctuations
and SSTs in the Indian Ocean appear to be complex. Although dry condi-
tions are frequently associated with a warmer than normal western tropical
Indian Ocean, this area is also an important source of atmospheric moisture
for southern Africa. It becomes the dominant source during the second half
of summer (Rocha and Simmonds, 1997), implying that an increase in SST
here could enhance rainfall over most parts of southern Africa. A warmer
tropical Indian Ocean also enhances the chances of tropical cyclone forma-
tion. Depending on the track, the tropical cyclones forming in the tropical
Indian Ocean may act to dry out eastern sections of the subregion or bring
floods. With a warm tropical Indian Ocean being capable of producing two
opposite climatic effects, SST-based seasonal climate forecasting becomes
a complex operation for much of southern Africa.

D rought Monitoring Techniques
In southern Africa most of the techniques used for drought monitoring
are heavily influenced by the meteorological definition of drought. The
rainfall index, the vegetation condition index, and the water requirement
satisfaction index are used to monitor the progress of the rainfall season
and its impact on agriculture.