Southern Africa's urbanization levels are currently just under the average for the Africa region, with 36 per cent of the sub-region's population living in urban areas (UNCHS 2001a). South Africa and Botswana are the most urbanized countries, with urban populations of 50 per cent each, and Malawi is the least urbanized with just 24 per cent of its population living in urban centres (UNCHS 2001a). This is considerably different from the situation 30 years ago, when just 11.2 per cent of the Southern African population lived in towns and cities (WRI, UNEP & UNDP 1992).
The current rate of urbanization is also high, and is predicted to average around 3.5 per cent over the next 15 years, although there are wide differences between countries. For example, South Africa, one of the most urbanized countries in the sub-region, has the lowest rate of urbanization, at 1.2 per cent per year, whereas Malawi, currently the least urbanized, has estimated urban growth rates of over 6 per cent per year (UNCHS 2001a). South Africa has the biggest and most numerous urban areas in the sub-region, including Southern Africa's largest urban agglomeration, Johannesburg (population approximately 4 million, 791 000 households, area 1384 km2, 720 suburbs) (UNCHS & UNEP 1997, GJMC 1999).
The high urbanization rates in Southern Africa are due to rural-urban migration and high population growth rates. Migration is a result of the pull factors of urban settlements-such as perceived job opportunities, and better infrastructure and housing-in addition to 'push factors' from rural areas such as shortage of land and declining returns from agriculture. In Angola and Mozambique, urbanization has been driven largely by civil conflict which forced many rural residents to flee to relatively safer urban areas. About 4.5 million Mozambicans were displaced to urban areas during the 1980s (Chenje 2000).
Despite considerable economic development and employment opportunities in Southern Africa's urban centres, the rate of population growth and urban migration has exceeded the ability to create jobs and raise standards of living for urban residents. However, the informal sector has grown rapidly in urban areas, and many cities now have considerable hidden economies. One such informal activity is urban agriculture. Mainly instituted at the subsistence level to counteract low levels of employment and income, urban agriculture has become an integral part of the urban economy for the poor. Up to 37 per cent of urban households in Mozambique were engaged in subsistence agriculture in 1996, and 45 per cent of low-income urban households in Zambia grew crops or raised livestock (UNDP 1996).
The rapid growth and expansion of urban areas in Southern Africa are causing an unprecedented level of localized depletion of natural resources, discharge of unprocessed wastes into the environment and massive demands for urban services. Most Southern African municipalities have not been able to keep pace with the demand for basic services such as housing, roads, piped water, sanitation and waste disposal. Provision of health and education services and facilities has also lagged far behind urban population growth. The overall result is that the environment has become hazardous to human health through rapid spread of water-borne and respiratory diseases, and this situation is compounded by a lack of health facilities, low levels of education and employment opportunities and, hence, a reduced ability to afford improvements to living conditions.