Most Western African countries are well-endowed with freshwater, except for those bordering on the Sahel, which frequently experience drought. Accessibility to freshwater and its integrated management nonetheless remain major concerns in western Africa. Inappropriate management of freshwater, and competition between user groups, limit efforts by governments and the international community to encourage economic development and to improve the standard of living in western Africa. There are also rising concerns over freshwater quality, in terms of pollution from domestic effluents and industrial wastewater, particularly in the coastal zone.
With the exception of Cape Verde, all the countries in the sub-region share surface water resources with one or more other countries. The sub-region is drained by three major basin systems. The Niger basin drains an area of 2 million km2 (33 per cent of the total surface area of the sub-region), and involves 9 of the 16 subregional countries, including Cameroon and Chad. Other important basins are: the Senegal basin, shared by four countries; the Gambia basin, shared by three countries; the Bandama basin in Côte d'Ivoire; the Comoe basin, shared by four countries; and the Volta basin, shared by five countries. The sub-region's freshwater resources are unevenly distributed between countries. Liberia, for example, has internal renewable water resources of more than 63 000 m3/capita/yr, and Mauritania has only 150 m3/capita/yr (UNDP and others 2000). Temporal variation in rainfall is common throughout the subregion, but only those countries in the northern Sahelian zone (Mali, Mauritania, and Niger) regularly experience drought, whilst countries in the wetter coastal belt are periodically affected by floods.
Three major types of groundwater aquifers are observed in the region, namely: basement aquifers; deep coastal sedimentary aquifers; and superficial aquifers. The availability of groundwater varies considerably from one type of substrate to another, and according to the local levels of precipitation and infiltration, which determine the actual recharge. In Mauritania, for example, internal renewable groundwater resources are estimated at 0.3 km3/yr (FAOSTAT 1997), and these are important sources of water for domestic use, irrigation and livestock watering. About 400 000 people live in the 218 oases, and are dependent on 31 400 wells, extracting the water manually (FAOSTAT 1997). The water is used to irrigate 4 751 ha of palm trees, with 244 ha of annual crops under them (FAOSTAT 1997).
Six Western African countries are expected to experience water scarcity by 2025, namely: Benin; Burkina Faso; Ghana; Mauritania; Niger; and Nigeria (Johns Hopkins 1998). Climate change is predicted to bring about reduced rainfall and increased evaporation in the areas to the north, advancing the rate of desertification in the Sahel (IPCC 2001). Countries in the coastal zone may experience more intense rainfall and increased run-off. Combined with existing high rates of deforestation and degradation of vegetation cover, this could have serious consequences for soil erosion and agricultural productivity.
Figure 2e.10: Water use by sector in Western Africa, 1900-2025
Source: Shiklomanov 1999
Demand for water has been steadily increasing in all sectors, as a result of population growth; commercial agricultural expansion; and industrial development. Current total withdrawal of water for domestic, industrial and agricultural consumption is 11 km3/yr, and demand for water from all sectors is expected to increase to some 36 km3/yr by 2025, as shown in Figure 2e.10 (UNDP and others 2000, Shiklomanov 1999).
The Volta and Niger rivers have been dammed to supply water for irrigation and domestic consumption, as well as to generate hydroelectric power. However, this has created problems of accelerated erosion in the coastal zone, as well as marginalization of pastoralists, who are dependent on seasonal floods (for example, Acreman 1999). Despite agriculture being the largest water user, accounting for 70 per cent of all withdrawals in the sub-region in 1995 (Shiklomanov 1999), irrigation potential remains largely untapped, especially in the Sudano-Sahelian zone, where only 16 per cent (5.3 million ha) of potentially irrigated lands have been developed (Falloux and Kukendi 1988).
Access to piped water and sanitation also remains low, despite considerable improvements during the International Drinking Water Supply and Sanitation Decade (1981-1990). In 2000, total water supply coverage was highest in Senegal (78 per cent) and lowest in Sierra Leone (23 per cent), with most urban areas in the sub-region better supplied than rural areas (WHO/UNICEF 2000).