Monitoring Agricultural Drought in Southern Africa - Monitoring and Predicting Agricultural Drought: A Global Study - page 269

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Fig ure 20.2 Time series of Zimbabwe smallholder-farming sector maize yields and annual
rainfall from 1970 to 1999.

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ov er Zimbabwe, for example, exceeds 40% in the drier west and south-
w est sections of the country and is below 25% in the north (figure 20.5).
R ecent studies of interannual rainfall variability over southern Africa have
de monstrated their periodic nature. Historical rainfall records generally
sh ow spectral peaks in five bands, 2.2-2.4, 2.6-2.8, 3.3-3.8, 5-7, and 17-
20 years (Nicholson, 1986; Makarau and Jury, 1997). It has been argued
th at these periodicities in annual rainfall are indicative of the influence of
th e Quasi-Biennial Oscillation, ENSO, periodic sea-surface temperature os-
ci llations, and the luni-solar cycles (Nicholson, 1986; Makarau and Jury,
1997).

Line
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Norm
PgEn

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ENSO

C onsiderable evidence exists that phase shifts in the ENSO are accompa-
ni ed by rainfall anomalies across southern Africa (Ropelewski and Halpert,

Figure 20.3 Response of Zimbabwe's GDP growth rate to rainfall.