An analysis of onset date and rainy season duration over Zambia |
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| Authors: | S Hachigonta C J C Reason M Tadross |
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| Institution: | (1) Department of Oceanography, University of Cape Town, Private Bag, Rondebosch, South Africa |
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| Abstract: | Summary This study investigates the onset and cessation dates of the main summer rainy season over Zambia, their interannual variability,
and potential relationships with ENSO and regional circulation anomalies. Focus is placed on onset and cessation dates because
these rainy season characteristics are often of more relevance than seasonal rainfall totals to user groups such as farmers,
water resource managers, health and tourism officials.
It is found that there is substantial interannual variability in these parameters with some indications of a relationship
between anomalies in onset date and those in Ni?o3.4 SST, particularly over the northern part of the country. A strong gradient
exists between the south and the north in terms of rainfall amount, mean onset date and mean cessation date and all areas
of the country experience significant variability.
Analysis of circulation anomalies for early (late) onset seasons over northern Zambia shows that they are characterised by
anomalous ridging (troughing) over and south of South Africa, a weaker (stronger) Angola heat low and enhanced (reduced) low
level moisture flux into eastern Zambia from the Indian Ocean. The connection with ENSO during the onset season of austral
spring appears to arise both through changes in the amount of subsidence over southern Africa as well as via the so-called
Pacific South America pattern that extends across the South Pacific and South Atlantic towards southern Africa.
Authors’ address: S. Hachigonta, C. J. C. Reason, M. Tadross, Department of Oceanography, University of Cape Town, Private
Bag, Rondebosch 7701, South Africa. |
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