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
Originating
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. |
2.3.2.1. 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
Countries |
Basin Area
(1,000 km2) |
Basin Countries |
|
Congo
Zambia,
|
9 |
3,720 |
Zaire, Central African Republic, Angola, Congo, Tanzania, Cameroon,
Burundi, Rwanda |
Nile
Zaire, |
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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