by Caiphas Chimhete
This is the second in a four part-series on Water, based on the book Water in Southern Africa published by SADC. IUCN and SARDC in February 1997.
Determining the minimum amount of water needed to sustain the ecosystem is a key aspect for environmental planners in southern Africa, if the present flora and fauna are to be preserved and maintained.
A new book, Water in Southern Africa, says it could be necessary in future to determine minimum amounts of water needed for ecosystems to survive, especially during the drought periods.
A large percentage of the potentially available water is needed for nature conservation and ecological purposes in SADC countries. In South Africa, for example, the quantity of water required for adequate environmental management is projected to reach 2,954 million cubic metres by the year 2000. This would be about 13 percent of the total water demand in that country.
The book also notes that water planning should not only cater for domestic and industrial needs but also for preservation of natural resources that require water year round.
Engineers have for years considered all water as available for human use, but an environmental consciousness is beginning to develop in which natural resources and their water quantity or quality needs are taken into account when planning. Namibia’s Oanob Dam, for example, was specifically constructed to allow periodic release of water for ecological purposes in the ephemeral Oanob Rver to simulate flooding and maintain woodland growth.
Rainfall variation in the region affects the ecosystem more than total rainfall. Areas of low rainfall tend to have relatively little vegetation, limiting the number of animals which can live there while areas of high rainfall are more productive, but vegetation is often less nutritious. Extreme variations in rainfall, including droughts, can devastate an ecozone, with normal production reduced by more than 90 percent.
Lack of water brings death from thirst and hunger as drought kills plants on which wild animals feed. For example, the 1962 drought in Botswana nearly wiped out zebra, thousands of wildebeest and rhino. More recently, high wildlife deaths were recorded in Gonarezhou National Park in southeastern Zimbabwe due to drought in 1992/3.
Environmentalists are warning that water bodies (lakes, dams and rivers) of the region are threatened by foreign plants which are invading many catchments throughout southern Africa. The problem is worsened by a substantial decline in funding for the clearing for the alien plants over the years.
Alien plants like water hyacinth or fynbos consume three-and a half times as much water from dams or lakes compared to evaporation. The plant sucks water which then evaporates into the air. Through this process the hyacinth weed contributes significantly to the water loss from the surface of water bodies.
Efforts to clear the weed are proving fruitless.
It appears the issue of these alien plants has not been prioritised in the region yet the problem is “very serious,” according to Dr Brian van Wilgen of World Wide Fund for Nature (WWF) who recently headed a team to South Africa to assist key decision-makers to be aware of the enormous implications of the alien plants. If left unchecked, the problem may result in the region losing a significant portion of its water supply.
Major cities in southern Africa have their water bodies threatened by such plants. Cape Town’s water supplies are seriously threatened by the plants which recently invaded catchments and are using more of the water than indigenous plants.
In Zimbabwe’s Lake Chivero, large amounts of water are lost everyday due to an alien weed, the water hyacinth. Other towns and cities are also threatened though on a smaller scale. Water plants multiply quickly, thus increasing the rate of water loss. Governments have employed manual labourers and machines to remove the weeds from water bodies.
The book recognises the importance of the region’s wetlands which should be conserved as they retain a large volumes of water for ecosystem maintenance. They are important as habitat for wild species and for agricultural purposes during the dry season.
Wetlands or dambos – as they are known in some parts of the region – store large quantities of water during the wet season and gradually release it during the dry season, making agriculture possible even in when it is dry. Areas with darnbos are a major player in economic activities of this region as they produce agricultural products throughout the year.
In the Zvishavane district in southern Zimbabwe– a hilly region with limited resources, low productivity and only 450-650 mm of rainfall annually — dambos are crucial to the survival of local people.
The dambos occupy about 10 percent of central southern Africa, including parts of Angola, Malawi,
Mozambique, Tanzania and Zimbabwe.
Wetlands also support a high biological diversity. Most important species of fish, reptiles, amphibians, birds and mammals have been recorded in wetlands such as Okavango Delta, Bangweulu, Lake Malawi and Zambezi floodplain. The presence of a wide range of animal species and vegetation in these water bodies show the need to consider water for the environment in southern Africa in any water planning.
The presence of a variety of animal species is also an economic asset for the region as it brings foreign currency from visiting tourists. Some of the region’s protected areas have been classified as world heritage sites in recognition of their international ecological significance. For example, Lake Tanganyika has 1 300 species – of which more than 500 are found nowhere else — making it a unique tourist destination site.
Southern Africa – with its depleting natural resources– needs to manage its water bodies to preserve the remaining resources not only for future generations, but for economic purposes. (SARDC)
