Biology Reference
In-Depth Information
As we flew over the Etosha pan in Namibia and the North Eastern part of the Kalahari
Desert, the sparse vegetation six miles below became less visible as the smog cloud thickened.
To the left of our path were the fingers of the Okavango swamps covering 68,000 square km,
filled with water from the 200 yard wide Kavango river, where I had been stationed, flowing
1100 km from the Angola highland to Rundu and then 660km on to the interior of the Kalahari
Bushveld and what was once a large inland ocean.
Oxbow Lakes on Boteti River
The climate of Sub Saharan Africa has been dominated since the last glacial maximum by
the interaction of two weather patterns, namely the Mediterranean winter rains and the Inter-
tropical Convergence Zone (ITCZ) where moisture from the tropics of Cancer and Capricorn
converge. This brings rain to more southern parts during November to April, but the
distribution varies greatly. Summer rainfall related to the ITCZ extends south to 15-20 degrees
because a low pressure system over Southern Africa draws moisture from the tropical Atlantic
(remember in the Southern Hemisphere low pressure cells spin clockwise not anti-clockwise)
by tropical westerly air flow, and further south from easterly air flow off the Indian Ocean.
The southwest Indian Ocean sea surface temperature (SST) also influences Africa's rainfall by
the heat creating the low pressure system that draws the low pressure system southwards and
hence the ITCZ. However, based on Zambezi river sediment discharges, Schefub, Kuhlman et
al. reported in Nature 2011 that the stronger influence on rainfall and the ITCZ is the effect of
the cold artic northern high latitudes. The severe dry spells in Africa during the Younger Dryas
and Heinrich Stadila 1 these were also caused by the arctic cold events forcing the ITCZ
further south than presently, drying central Africa but increasing moisture further south. The
western side of the Southern Africa ITCZ rainfall area is however blocked from obtaining
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