Urban centres, and cities in particular, have developed from administrative and transport centres to commercial hubs, and centres of education and technology, manufacturing and processing, trade, and employment. Urban dwellers have lifestyles that contrast starkly with those of their rural forebears or contemporaries, not least in their interactions with the environment. In the majority of nations, cities generate the lion's share of economic activity, ultimately consume most of the natural resources, and produce most of the pollution and waste. These problems are usually associated with unplanned or unserviced settlements (slums) where predominantly poor inhabitants do not have access to adequate housing, water supply, sanitation, waste disposal, or electricity. These are also highly visible impacts and affect the health and well-being of many millions of people. However, environmental degradation is caused as much by the excessive consumption of resources (especially water) and generation of non-biodegradable wastes prevalent in affluent urban areas as it is by illegal dumping and burning of sewage and solid wastes in informal settlements (e.g. Napier 2000). The key requirements for sustainable urban growth are:
Unplanned settlements often lack basic services.
The high rate of growth of urban populations in Africa has resulted partially from an increase in the number of urban households, brought about by changes in standards of living and attitudes towards familial dependence. The rate of growth in number of households across Africa averaged 3.1 per cent between 1985 and 2000, and is set to continue at this rate until 2030 (UNCHS 2001a). The consequent increase in demand for basic housing and services for urban populations, as well as skewed distribution of investment towards affluent suburban developments, has resulted in the rapid expansion of illegal or unplanned and unserviced settlements, with unhealthy living conditions and extreme overcrowding. For example, in 1993, about 55 per cent of Nairobi's population lived in informal settlements (USAID 1993), and in South Africa, nearly half the population did not have adequate housing in the late 1990s (DEA&T 1999). In Monrovia, Liberia, 42 per cent of households were reportedly living as squatters in 1998 (UNCHS 2001c). Furthermore, only 60 per cent of urban dwellings in Africa are considered permanent, and almost half fall short of compliance with regulations (UNCHS 2001b). In African cities the average person has just 8 square metres of floor space, indicating conditions of extreme overcrowding. By comparison, residents of Asian cities have 9.5 m2, in industrialized countries the average is 34.5 m2, and the global average is 13.6 m2 (UNCHS 2001b). Overcrowding exacerbates rates of transmission of infectious diseases, such as gastro-intestinal infections, and respiratory diseases such as tuberculosis, commonly associated with poor ventilation and air pollution.
In spite of their contribution to national economies, African municipalities receive only 14 per cent of GDP in revenue-an average of US$14 per capita per year and two hundred times less than the revenue of municipalities of high income countries
Low revenue in African municipalities, and consequently low spending, has led to development and maintenance of infrastructure being severely curtailed. In spite of their contribution to national economies, African municipalities receive only 14 per cent of GDP in revenue-an average of US$14 per capita per year and two hundred times less than the revenue of municipalities of high income countries (UNCHS 2001b). They spend only US$12 per capita per year. This situation has been further compounded by slow economic growth over the past three decades and a bias amongst donor organizations in favour of development projects in rural areas.
Figure 2g.2: Regional cost of water
Source: UNCHS 2001b (p 41 State of World Cities Report)
An additional concern is that the poor often pay higher prices for housing and associated services. In African cities, people spend approximately 40 per cent of their incomes on rent, with the Arab nations paying the most at 45 per cent. This is over twice the amount paid by residents of higher income countries and indicates the high demand for housing and slow rates of provision of rented accommodation in Africa (UNCHS 2001b). Local governments are attempting to address this issue by increasing the production of low-cost housing stocks, and introducing housing subsidies for low-income groups (Department of Housing 2000, UNCHS 2000). However, tremendous backlogs still exist, as housing development falls short of population growth and urbanization rates. The residents of informal urban settlements often pay more for access to water (see Figure 2g.2), whereas water rates to planned suburban developments and industrial and agricultural users can be heavily subsidized (UNCHS 2001b).
Access to water supply, sewerage, electricity and telephone in African cities ranks the lowest in the world (UNCHS 2001b). Overall access to improved water sources in urban areas in Africa has increased marginally, from 84 per cent in 1990 to 85 per cent in 2000. However, 'improved water' includes household connection, public standpipes, boreholes, protected dug wells or springs, and rainwater collection (WHO/UNICEF 2000). Similarly 'improved sanitation' includes connection to a public sewer or septic system, a pour-flush toilet, a simple pit latrine, or a ventilated pit latrine (WHO/UNICEF 2000). The overall figure for access to sanitation in African towns and cities declined marginally from 85 to 84 per cent in the same period (WHO/UNICEF 2000). Poor water supply and sanitation create conditions conducive to high rates of waterrelated diseases such as cholera, dysentery, scabies, and eye infections. Diarrhoea and dysentery are among the most prevalent childhood diseases and a significant cause of under-five mortality. They correlate strongly with lack of availability of clean water (UNCHS 2001b). In addition, health and education facilities in unplanned settlements are often under-resourced or unaffordable, and unemployment and poverty are rife.
Unplanned settlements can, however, also be important economic centres, contributing to the informal economy through provision of services such as food provision and sale, domestic services, car and household maintenance, hairdressing, and childminding, as well as trade and recycling (e.g. Napier, Ballance & Macozoma 2000). A good example of the contribution of the informal sector is the 'Zaballeen', a group of informal waste collectors in Egypt who separate and recycle different types of waste, thereby providing a valuable service to the urban environment whilst also making a living (UNCHS 1999).
Environmental impacts of rapid, unplanned, urban growth include loss of natural habitats, changes in and sometimes loss of biodiversity, as well as alterations to ecological functions such as hydrological cycles and atmospheric exchange. Fragile environments such as delicate slopes, natural drainage waterways, and floodprone areas, are at risk from rapid urbanization. In unplanned settlements-where space is at a premium and shelters are erected on steep slopes, on wetlands, or in flood zones-not only are residents at risk from flooding and subsidence, but the ecosystems are also vulnerable to pollution and physical degradation. Residents of Johannesburg's Alexandra Township were devastated by flooding and suffered loss of property and outbreaks of cholera in early 2000. In Cairo, the risk of earthquake puts millions of people in dense and insufficiently stable urban settlements in danger of loss of life and property. Improved planning, reductions in the backlog of low-cost housing, and improved disaster early warning and preparedness schemes are required to reduce this threat.