Southern Africa is mostly semi-arid, and experiences variation in rainfall, both over time and between countries. This sub-region is also expected to experience further variability in rainfall, reduced precipitation and increased evaporation, as a result of climate change. With a rapidly growing population, and demands from the domestic, agricultural and industrial sectors for water, freshwater availability is a priority concern for the sub-region. Discriminatory access policies and pricing systems have also skewed the distribution of access to water resources across population groups. An additional concern in the subregion is declining water quality due to domestic and industrial pollution, and eutrophication and salinization due to agricultural pollution.
Southern Africa’s annual average surface water resources are approximately 534 km3/yr, but they are distributed unevenly due to: frequently low and variable rainfall; terrain; evaporation rates; and vegetation and soil cover. For example, Angola, the wettest country in the sub-region, has average annual internal water resources of 184 km3/yr (14 000 m3/capita/yr), and Mozambique and Zambia have 100 km3/yr and 80 km3/yr respectively (5 000 m3/capita/yr and 8 700m3/capita/yr). By contrast, the driest countries, Botswana and Namibia, have just 2.9 km3/yr and 6.2 km3/yr respectively (1 700m3/capita/yr and 3 500m3/capita/yr respectively) (UNDP and others 2000).
The areas of low rainfall are in many cases also coincidental with areas of highest evaporation potential, and variability in rainfall can result in periodic episodes of severe and prolonged droughts, particularly in the southwest. In these areas, groundwater resources are particularly important (see Box 2e.7). By contrast, the northern and eastern areas are subject to occasional floods, the most recent example being in 1999–2000. The excessive rains of this season affected Mozambique, Botswana, Zambia, Zimbabwe and South Africa. Some 200 000 ha of cropland were flooded and more than 150 000 families were affected. The estimated cost of recovery is millions of US dollars (Mpofu 2000). Although the SADC Early Warning System was able to predict the heavy rains, most countries were ill-prepared for the magnitude and duration of the floods, stimulating investigations and revisions of response strategies.
|Box 2e.7 Importance of groundwater in Southern Africa|
|Source: Chenje 2000|
Lake Malawi has the largest number of fish species of any lake in the world, estimated at more than 500 species, of which 90 per cent are thought to be unique to the lake. The most important species biologically, and in terms of local livelihoods, are the 400 or more cichlid species, of which all but five are endemic to Lake Malawi
The sub-region’s largest freshwater lake, and the third largest lake in Africa, is Lake Malawi, with a surface area of 31 000 km2. The lake is important in terms of fishing activities and the tourist industry which it supports. Lake Malawi has the largest number of fish species of any lake in the world, estimated at more than 500 species, of which 90 per cent are thought to be unique to the lake. The most important species biologically, and in terms of local livelihoods, are the 400 or more cichlid species, of which all but five are endemic to Lake Malawi (Ribbink, Marsh, Ribbink and Sharp 1983). Because of this extraordinary biodiversity, the southern part of the lake is registered as a national park, and was established as a Natural World Heritage Site in 1984. Major rivers include the Zambezi River, whose basin is shared by eight southern African countries and is home to 40 million people. The Zambezi basin also supports many local communities, as well as commercial agriculture and forestry, manufacturing and mining, conservation and tourism (Chenje 2000).
A study of the potential impacts of climate change on freshwater resources in southern Africa predicts an overall reduction in rainfall, by as much as 10 per cent across the whole sub-region, and up to 20 per cent in parts of South Africa (WWF 2000). Evaporation rates will increase by 5–20 per cent, as a result of raised temperatures, which will reduce run-off, and decrease water security and agricultural potential. Coincident with this will be increases in the frequency and intensity of flooding and drought (WWF 2000). In addition to variability and long-term decline in precipitation, water resources development is further complicated by the uneven distribution of population—particularly, high population densities in arid areas. Per capita average annual water resources in Angola, for example, exceeds 14 000 m3/capita/yr whereas, in South Africa, each person has only slightly more than 1 000 m3 per year (UNDP and others 2000).
Environmental degradation is a further contributor to decline in water availability, through loss of vegetation, and the disruption of microclimates and hydrological cycles. Dense stands of alien vegetation in southern Africa are particularly disruptive in this regard, because they use much larger amounts of water than indigenous species (see Box 2e.8). In some areas of southern Africa, up to 50 per cent of wetlands have been transformed, and the Caprivi wetland system (Namibia) has been reduced to almost 25 per cent of its original size. This has been due to: draining of wetlands, for agricultural or infrastructure development; reduced flows; aquatic weeds choking water courses; increasing use of pesticides; and overextraction of reeds, wood and other materials for construction, weaving and crafts (Chenje 2000). Wetlands act as sponges, absorbing excess water in times of heavy rainfall and, thus, buffering the effects of flooding. To prevent further degradation of these important habitats, two countries of the sub-region, South Africa and Zambia, are parties to the 1971 Ramsar Convention, and have designated certain areas as Wetlands of International Importance.
|Box 2e.8 Alien invasive vegetation and water use in southern Africa|
|Sources: MacDonald 1989, Chenje 2000,MacDonald and Richardson 1986, Global Water Partnership 2000,Working for Water 2000|