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Where does the rain come from?

The important thing to bear in mind, is that the amount of rainfall in the Chobe/Zambezi confluence, in and around the Eastern Caprivi, has very little to do with the volume of water in these two rivers. The Chobe, which starts life as the Kwando has its headwaters in the Angolan highlands, beyond Cangamba, 1200 kilometres north of Kasane. The Zambezi starts on its way to the Indian Ocean in northern Zambia, on the border of the Congo. As the areas where these to rivers get their start falls into the Tropical Zone the air is hot and humid, conducive to rain. By way of comparison, the Headwaters of the Zambezi receives upwards of 1200mm of rain, the Kwando upwards of 1100mm, while Kasane averages 500mm per annum.

There are two major climate systems that affect the Zambezi/Kwando catchment, the first is the Inter-Tropical Covergence Zone (ITCZ) which brings moisture from the tropical north. The second is the series of high pressure anticyclone cells that move across the Southern Africa, bringing dry cool air into play. These two weather systems move northward in winter, bringing dry cooler conditions to the southern African sub-continent.  In the summer the ITCZ moves southward with the southerly movement of the sun from the Equator. Most of the moisture in the ITCZ is drawn in from the Indian Ocean Trade winds as well as from the Atlantic Ocean, across the Angolan Highlands and the Congo Basin. The further southwards the ITCZ moves, the wetter the summer, generally in southern Africa

There are two peaks in the rainfall in the catchment areas of the Zambezi/Chobe Rivers, one in November-December as the ITCZ moves southwards and again in March-April as it retreats nothwards. During January-February the Zone is further south over the Caprivi/nothern Botswana, and they consequently receive their best rain then. Because humidity is at its highest in the rainy season the highest rainfall in the catchment areas is generally January to March, and it is this large volume of water, that has to travel 1200 kms. over largely very flat terrain that ensures the flood can last up to two months after the last rain in Kasane.

By |February 10th, 2014|Voyager|Comments Off on Where does the rain come from?

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