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Preface Annex 1
INVENTORY OF RESOURCES
Rainfall and rivers
Africa has virtually the same climatic zones in the northern and southern hemisphere, and these zones are arranged symmetrically on either side of the equator. The zones are determined mainly by latitude, except in the east where highlands greatly modify the climate.
Africa is predominantly a tropical region: only its northern and southern extremes, which are directly influenced by mid-latitude westerly winds, are considered to have temperate climates. Nevertheless, it is, after Australia, the driest region in the world (ECA 2000). The amount, duration and seasonal distribution of rainfall are the most important factors differentiating its climates. Africa has six climatic zones. These are equatorial, savannah, semi-arid, arid, highland and Mediterranean:
Most of the African continent receives moisture from air originating over the Atlantic Ocean. In the eastern part, however, rainfall south of the equator comes from large tropical cyclones originating over the Indian Ocean during the southern hemisphere summer. Rainfall from these cyclones is particularly high in eastern Madagascar and the coastal mainland between South Africa and southern Tanzania.
Average rainfall has decreased since 1968, and has been fluctuating around a notably lower mean (UNEP 1999). In Africa, some 3 988 km³ of renewable water is available annually (ECA 2000). In recent years, the pattern of rainfall has tended to extremes, with the severity and frequency of droughts and floods increasing.
Africa has many rivers, but some, particularly in the mountainous areas, are seasonal and the water flow rates are gradually declining over the years.
The major rivers include the Senqu or Orange, Niger, Zambezi, Limpopo, Senegal, Congo and the Nile. The Nile is the longest river in the world, at about 6 679 km (Pickett 2000). The Nile starts from Lake Victoria and passes through Uganda, Sudan and Egypt to the Mediterranean Sea. The main headstreams, the Blue Nile and the White Nile, join at Khartoum in Sudan to form the Nile proper. The Senqu/Orange River is 2 092 km long and passes through Lesotho, South Africa and Namibia, flowing south-west, north-west, and west to the Atlantic Ocean (Pickett 2000). The Niger River is found in Western Africa, rising in Guinea and flowing about 4 183 km in a wide arc through Mali, Niger and Nigeria to the Gulf of Guinea (Pickett 2000). The Zambezi River is about 2 735 km long, rising in northwest Zambia and flowing south and west to the Mozambique Channel (Pickett 2000). The Limpopo River runs through South Africa, flowing about 1 770 km in a north-east-south-east arc to the Indian Ocean in southern Mozambique (Pickett 2000). The Congo River is 4 666 km long and flows through Congo and the Democratic Republic of the Congo to the Atlantic Ocean (Pickett 2000). The Congo, which alone accounts for some 38 per cent of the continent’s discharge into the ocean, drains an area of more than 4.1 million km², ranking second only to South America’s Amazon River in terms of discharge and size of drainage basin (Microsoft Encarta Online Encyclopaedia 2005). The Congo River basin alone holds almost 30 per cent of Africa’s total fresh surface water reserves and the world’s largest hydropower potential in any one single river basin (ECA 2000). Africa’s rivers provide extensive hydropower potential including for large (> 500 MW), medium (> 10 MW, < 500 MW) and small (< 10 MW) plants. The opportunities and challenges associated with Africa’s rivers and freshwater systems are discussed more fully in Chapter 4: Freshwater.