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The Limpopo River Basin
 Introduction
Geography
Climate and Weather
 Principles of Climate and Weather
 Climate of the Limpopo Basin
The Regional Climate
 Climatic Patterns
 Climatic Variability
 Climatic Classification
 Water Scarcity
 Drought
 Cyclones
 Climate Change
Hydrology
Water Quality
Ecology and Biodiversity
Sub-basin Summaries
 References

 



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Climate of the Limpopo River Basin: The Regional Climate  

Southern Africa can be broadly divided into two Köppen climatic groups:

  • Class B - Arid climates: The first group comprises 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.
(Sources: Pidwirny 2006; INGC/ FEWS NET Mind 2003).

To see a map of the distribution of these climatic classes in the Limpopo 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. The wet season occurs when the Inter-Tropical Convergence Zone (ITCZ) (Allaby and Allaby 1999) moves south, bringing rainfall and the dry season occurs when the ITCZ retreats northward.

Oceans play an important role in the region’s climate. 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. By contrast the west coast is influenced by the cold Benguela current from the Atlantic Ocean, which produces a drier 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.

Inter-Tropical Convergence Zone (ITCZ) variation across Africa throughout the year.
Source: Ker et al. 1978
( click to enlarge )

Rainfall in southern Africa is strongly influenced by the 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 above figure 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).

 



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