The Regional Climate

The Southern African region can be broadly divided into two Köppen Climatic Groups:

• Class B - Dry climates: Comprising the southwestern countries bordering the Kalahari Desert: Angola, Botswana, Zimbabwe, Namibia and South Africa, with climates ranging from semi-arid and sub-humid in the east, to hyper-arid in the west.

• Class C - Moist mid-latitude climates with mild winters, comprising the eastern countries Tanzania, Malawi, Mozambique, Swaziland, Lesotho and the Indian Ocean island countries, with climatic conditions ranging from Dry to Moist Subtropical Mid-Latitude conditions.

To see a map of the distribution of these climatic classes in the Kunene River basin, please refer to Climatic Classification of the Basin.

Southern Africa is located between the Atlantic Ocean and Indian Ocean high pressure zones on the west and east, respectively. The region is prone to frequent droughts and uneven rainfall distribution. The region has two distinct seasons – a wet season roughly from November to April and a dry season roughly from May to October.

Rainfall in southern Africa is strongly influenced by the Intertropical Convergence Zone (ITCZ). The ITCZ changes position during the year, moving between the Equator and the Tropics of Cancer and Capricorn. Southern Africa normally receives the bulk of its annual rainfall from November through March as the ITCZ moves south. The further south the zone moves, the more promising the rainy season (Allaby and Allaby 1999). The average positions of ITCZ in July and January in the figure below illustrate this situation.

In a normal southern African rainy season, the ITCZ influence covers central Tanzania to southern Zimbabwe and is associated with favourable rainfall. The “Botswana High” pressure system tends to push the ITCZ away, often resulting in periods of drought, (International Research Institute 2000).

Inter-Tropical Convergence Zone (ITCZ) variation across Africa throughout the year.

Source: Ker et al. 1978

( click to enlarge )

Oceans play an important role in the region’s climate. Angola and Namibia on the west coast are influenced by the cold Benguela current from the Atlantic Ocean, which produces a drier climate. By contrast the east coast is influenced by the southward-flowing Mozambique current, which brings warm water and humid air from the Equator and creates a humid, warm climate. 

In the interior of southern Africa there is a strong rainfall gradient from east to west. In Swaziland and Lesotho to the east, both altitude and exposure to moist air coming off the Indian Ocean produce the heaviest and most reliable rainfall. Total rainfall gradually decreases westward, so that much of the central and western regions are semi-desert with low and variable rainfall.

Over the whole of this interior region, rainfall mainly occurs in the summer season in the form of thunderstorms. There are also large daily and seasonal temperature ranges as a result of the effects of altitude and “continental” position (the lack of ocean influences). Winters are usually dry and sunny, while summers are wet and hot. Frost is a frequent occurrence in winter and snow is common above 1 500 meters. This variability in weather patterns, possibly due to climate change, sometimes results in droughts and floods, which adversely affect human activities.