The Regional Impacts of Climate Change

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2.3.2. Hydrology and Water Resources

Water resources are inextricably linked with climate, so the prospect of global climate change has serious implications for water resources and regional development (Riebsame et al., 1995). Efforts to provide adequate water resources for Africa will confront a number of challenges, including population pressure, problems associated with land use such as erosion/siltation, and possible ecological consequences of land-use change on the hydrological cycle. Climate change will make addressing these problems more complex.

Table 2-3: Dependence on external surface water-selected countries (after Gleick, 1993).

Country %Total Flow
Outside Border
Ratio of External
Water Supply to
Internal Supply(1)

Egypt 97 32.3
Mauritania 95 17.5
Botswana 94 16.9
The Gambia 86 6.4
Congo 77 3.4
Sudan 77 3.3
Niger 68 2.1
Senegal 34 0.5

(1) "External" represents river runoff originating outside national borders; "internal" includes average flows of rivers and aquifers from precipitation within the country. Hydrological Systems

Africa has several surface water bodies spread throughout the continent. Table 2-2 lists the 10 largest surface-water bodies in sub-Saharan Africa, along with basin countries and basin area (after Rangeley et al., 1994). Other smaller water bodies exist within country boundaries. Africa has the greatest number of rivers and water bodies that cross or form international boundaries. The 10 river basins in Table 2-2 (including Lake Chad) have a total drainage area greater than 350,000 km2, and they combine to affect 33 sub-Saharan countries and Egypt. Sharma et al. (1996) assert that few of the transboundary river basins in the region are effectively jointly managed. Effective management would require treaties, political commitment, institutions, capacity, information, and finance. National interests often override regional objectives. The large number of countries belonging to multiple river and lake basins makes regional cooperation very difficult. Table 2-3 shows dependence on external surface water for selected countries. Coordinated action among African countries will determine whether countries in the region can effectively adapt to changes in the hydrology of African rivers and lakes.

Table 2-2: The 10 largest surface-water bodies in sub-Saharan Africa (Rangeley et al., 1994).

Basin No. of
Basin Area
(1,000 km2)
Basin Countries

9 3,720 Zaire, Central African Republic, Angola, Congo, Tanzania, Cameroon, Burundi, Rwanda
10 3,031 Sudan, Ethiopia, Egypt, Uganda, Tanzania, Kenya, Rwanda, Burundi
Niger 9 2,200 Mali, Nigeria, Niger, Guinea, Cameroon, Burkina Faso, Benin, Cote d'Ivoire, Chad
Lake Chad 6 1,910 Chad, Niger, Central African Republic, Nigeria, Sudan, Cameroon
Zambezi 8 1,420 Zambia, Angola, Zimbabwe, Mozambique, Malawi, Botswana, Tanzania, Namibia
Orange 4 950 South Africa, Namibia, Botswana, Lesotho
Okavango 4 529 Botswana, Angola, Namibia, Zimbabwe
Limpopo 4 385 South Africa, Botswana, Mozambique, Zimbabwe
Volta 6 379 Burkina Faso, Ghana, Togo, Cote d'Ivoire, Benin, Mali
Senegal 4 353 Mali, Mauritania, Senegal, Guinea


The major effects of climate change on African water systems will be through changes in the hydrological cycle, the balance of temperature, and rainfall. A case study of the impacts of climate change on the Zambezi and Nile River basins follows, based on Riebsame et al. (1995). Additional literature on the Zambezi basin includes Calder et al. (1996), Pinay (1988), Balek (1977), Conway and Hulme (1993), Vorosmarty and Moore (1991), Vorosmarty et al. (1991), and du Toit (1983).

The Nile and Zambezi basins are the second and fourth largest river systems in Africa; key geographic characteristics are depicted in Figure 2-9 and key hydrological characteristics given in Table 2-4. Both the Nile and Zambezi have a low runoff efficiency and a high dryness index, indicating a high sensitivity to climate change. Analysis showed the Nile as very sensitive while the Zambezi was fairly sensitive. Although the severity of the impacts of climate change depended primarily on the magnitude of change, the different hydrological sensitivities of the basins are also important. The Nile and Zambezi are especially sensitive to climate warming: Runoff decreases in these basins even when precipitation increases, due to the large hydrological role played by evaporation.

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