The average level of urbanization in Central Africa in 2000 was 48 per cent, ranging from 81 per cent in Gabon to 24 per cent in Chad (UNCHS 2001a). This represents rapid growth, over the last decade in particular, with urbanization rates of over three per cent for all countries, and reaching five per cent or more in Equatorial Guinea and Gabon. However, urbanization rates were even higher during the previous decade, when economic growth encouraged employment in urban areas. The largest cities in Central Africa are Kinshasa (5 million) in Democratic Republic of Congo (DRC) and Douala (1.6 million) and Yaoundé (1.4 million) in Cameroon (UNCHS 2001a).
Central Africa has a long history of urbanization. Cities or urban centres started as commercial, administrative and mining towns and as seaports during the colonial period. As a result many major or capital cities are on the coast (including Libreville and Douala) where access to trade, travel and international communications is enhanced. Libreville is the economic and administrative capital of Gabon, concentrating 50 per cent of the population, 50 per cent of employment, and more than 80 per cent of GDP. Douala is Cameroon's most important city and the man industrial centre. It is a port city with industries such as aluminium smelting, brewing, textiles manufacture, and processing of wood and cocoa. Kinshasa is also a port, on the Congo River estuary, and serves as the political, administrative, and industrial capital of DRC (UNCHS 2001c). Although cities have become the main catalysts of economic growth in Central Africa, urbanization has caused massive problems of poverty and environmental degradation.
Environmental consequences of the rapid urbanization and urban population growth include intensifying pressures on natural habitats and resources to satisfy the growing demand for space, housing, and water for drinking and sanitation. Municipalities and utility companies are unable to provide housing and infrastructure quickly enough to meet this demand and sub-optimal services are therefore provided, with suboptimal environmental standards and conditions.
Dualism between customary and modern tenure laws is also apparent in the urban centres and, together with high land and property prices, is one of the causes of unplanned or illegal construction. Rapid development of informal settlements or shantytowns ensues, characterized by overcrowding, unstable or unhealthy housing, inadequate water supply and sanitation, and lack of electricity supply and waste collection.
In Yaoundé, Cameroon, the majority of urban residents are squatters or tenants. There are conflicting pressures on residents to purchase properties and rents are high. However, property prices have also risen recently, while incomes have declined because of devaluation of the currency (UNCHS 2001c). By contrast, land prices in Douala are lower, and there is a much higher proportion of house owners and no squatter settlements (UNCHS 2001c). In the DRC, security of tenure is also complicated by disparities between modern legislation and traditional laws. For example, the DRC's 1973 Land Act stipulated that 'land is the exclusive inalienable and unprescriptable property of the state', but the acquisition of land remains subject to the consent of the land chief.
The city of Libreville, Gabon, is experiencing uncontrolled urban development resulting from a shortage of serviced plots, an absence of planning tools and instruments, and a lack of urban space control. The demand for housing stands at approximately 6 000 units per year (in a city with a population of 500 000), and available land for development is minimal (there are 14 hectares of 'green spaces' per 10 000 hectares) (UNCHS 2001c). The results are that over half of the population lacks proper housing; there is rapid development of unplanned, inadequately serviced, and often unsafe settlements; and illegal occupation is as high as 85 per cent (UNCHS 2001c).
One of the most important environmental impacts of uncontrolled urbanization in Central Africa is its spread into fragile ecosystems, including delicate or highly erodible slopes, natural drainage waterways or valleys, and areas that are subject to flooding. Due to the intense competition for space in urban areas, green spaces are rapidly disappearing and areas usually deemed unsuitable for housing are the only refuges available for the urban poor, who are then vulnerable to flooding, landslides, and outbreaks of pests and diseases. Although planning regulations are in place, they are poorly monitored and enforced. Development in and modification of green areas results in changes to biodiversity, risks of pollution of soil and water, changes to soil fertility and stability and, especially in wetland areas or areas where there is standing water due to lack of sanitation, high risk of disease transmission. Dense, unstable, and poorly sited settlements are also vulnerable to the impacts of floods, landslides, and fires.
Water supply and sanitation provision has also fallen behind rates of urban growth in many Central African cities, largely due to lack of municipal funds and capacities. On average, 59 per cent of the urban population has access to clean water (over 80 per cent in Cameroon and DRC), whilst 54 per cent has access to sanitation (but only 14 per cent in Congo and 25 per cent in Gabon) (WHO/UNICEF 2000). Inadequate water supply and sanitation pose a threat to human health via exposure to pathogens such as cholera and intestinal parasites. They also pose a threat to the surrounding environment if sewage and wastewater are discharged untreated. Untreated discharges contaminate soil and water bodies, creating a risk to human health via transmission of disease vectors or toxic elements, and threaten biodiversity through effects on the ecosystem such as eutrophication and contamination with heavy metals and inorganic compounds.