K. NSIAH-GYABAAH SUNYANI POLYTECHNIC, P.O. BOX 206 SUNYANI, BRONG AHAFO. GHANA Tel: ;

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1 URBANIZATION, ENVIRONMENTAL DEGRADATION AND FOOD SECURITY IN AFRICA PREPARED FOR POSTER PRESENTATION AT THE OPEN MEETING OF THE GLOBAL ENVIRONMENTAL CHANGE RESEARCH COMMUNITY, MONTREAL, CANADA, OCTOBER ABSTRACT K. NSIAH-GYABAAH SUNYANI POLYTECHNIC, P.O. BOX 206 SUNYANI, BRONG AHAFO. GHANA Tel: ; There are considerable implications of rapid urbanization and population growth for the future impact of global health, food security, global warming and environmental change. Although environmental conditions have arguably been potentially worse in the cities than in the rural areas in Africa, more attention has often been devoted to analysis of the impact of the rural poor on the environment and climate change. Recently, it is becoming clear that rapid urbanization threatens to turn the hope for a better future into an economic nightmare and human insecurity for millions of urban inhabitants in Africa. Accelerated environmental degradation, food insecurity and poverty, are crosscutting issues that result from rapid urbanization and urban population growth. This paper draws attention to the socio-economic and environmental implications of rapid urbanization and population growth in the developing countries with particular reference to Africa. It examines the urbanization process in Africa in the context of the environment, food supply and human security. It also focuses on the implications of rapid urbanization for sustainable development and human security in Africa. The main questions addressed are: What is the magnitude and what are the Causes of rapid urbanization in Africa? What are the implications of rapid urbanization for natural resources, environment, food supply and human security? INTRODUCTION Urbanization, simply defined as the shift from a rural to an urban society, is an essential corollary of industrialization that goes hand in hand with the role of human settlements as engines of growth in the economy and as promoters of scientific, socio-cultural and technological development. Urbanization is the outcome of the social, economic and political development. It is a factor of development associated with modernization and is a means of and consequences of modernization and has a positive and accelerating effect on development. In Africa, urbanization results from large concentrations of population in a few large cities and the factors that account for this phenomenon include: Industrialization and labour specialization 1

2 Higher productivity in agriculture due to specialization and introduction of new technologies Foreign penetration and power interests High expectations and hopes of groups and individuals Rapid urbanization finds expression principally in outward expansion of the built-up area, converting prime agricultural land into residential and industrial uses. It also leads to the construction of high-rise buildings and vertical commercial development in specific zones. AFRICA- LOCATION AND SIZE Africa, with a land area of 30 million square kilometers, is nearly three times the size of Canada. Although Africa has about 13 percent of the world s population, or some 813 million people, it has less than 1.6 percent of global trade, and 1 percent of global investments. Much of the continent lies in the tropical rain forest belt. The region also has a large stretch of desert (Sahara and Kalahari Deserts), woodlands and savannah grassland vegetation. It has many rivers with high potential for irrigation and hydro electricity. Africa has rich biodiversity and many tourist centers. It also has diversity of cultures and languages. AFRICA- CHALLENGES AND OPPORTUNITIES Africa is richly endowed with diverse natural resources including forests, gold, diamond, oil, copper etc. From Angola through Gabon to Libya and Nigeria, there are large deposits of crude oil. The wealth is enormous, but the richness has not led to a fulfilment of the aspirations of people for sustainable development on the continent. Africa is the least developed continent in the world. As a result of widespread poverty, Africa has a negative image as a continent in crisis, symbolized by environmental and social stress, in which disease, hunger, poverty, land degradation, ethnic conflicts and overpopulation threaten human security. Figure 1 shows the rich natural resources potential for sustainable development in Africa. 2

3 FIG. 1. NATURAL RESOURCES FOR SUSTAINABLE DEVELOPMENT OF AFRICA 3

4 WHAT IS URBANIZATION? Urbanization, simply defined as a radical shift from a rural to an urban society, is an essential corollary of industrialization that goes hand in hand with the role of human settlements as engines of growth in the economy and as promoters of scientific, socio-cultural and technological development. The process of urbanization in the developing countries, especially Africa is inexorable and rapid urbanization presents one of the greatest challenges to human security and sustainable development. In many African countries, urbanization has resulted in rapid population growth and concentration of people and industries in few urban areas such as Accra (Ghana), Lagos (Nigeria), Monrovia (Liberia), Abidjan (Cote d Ivoire) etc. Rapid urbanization finds expression principally in outward expansion of the built-up area, converting prime agricultural land into residential and industrial uses. It also leads to the construction of high-rise buildings and vertical commercial development in specific zones (See Fig. 2). Although urbanization is growing throughout the world, the growth of cities is more rapid in the developing countries especially Africa where annual growth rate is 1.6% compared to 0.8% in the developed countries. In 1950, Africa was the least urbanized continent with only 14.5% of the population in urban areas, but by 1988, about 35% of Africa s population of 749 million people was urban. UN projections indicate that the urban population will increase to 914 million by 2025 or 4 times the 1990 levels. FIG. 2 THE PROCESS OF LATERAL AND HORIZONTAL EXPANSION OF URBAN SETTLEMENTS 4

5 URBANIZATION PROCESS -GLOBAL TRENDS In 1990, the world s urban population was 2.4 billion, two thirds of who lived in the developing countries. By the year 2025, a United Nations study estimates that it will more than double, to 5.5 billion- a little larger than current total world population. The source states further that much of this growth would be in the developing countries, which will contain 4.4 billion people or 80 percent of world urban population by the year In the 20 th century, urban growth has reached unprecedented levels in many parts of the world, especially the developing countries. More than half of the world s population, approximately 3.3 billion people, was estimated to be living in urban areas in 2000 and it is estimated that the population inhibiting urban areas would rise to 65 per cent by the year 2020 (UNFPA, 1991). In 2000, there were 17 of the world s 25 megacities with populations exceeding 10 million, such as Lagos in Nigeria, Seoul in the Republic of Korea, Buenos Aires etc, were in the developing countries. Mexico city had about 25 million people, Sao Paulo in Brazil had 22 million, and Bombay and Calcutta in India and Shangai in China each had 15 million. Today there are 19 cities with 10 million or more people; 22 cities with 5 to 10 million people; 370 cities with 1 to 5 million people; and 433 cities with 0.5 to 1 million people (UNCHS 2002). URBAN POPULATION AS PERCENTAGE OF TOTAL POPULATION BY REGIONS 5

6 More than 90 per cent of future population growth will be concentrated in cities, mainly in developing countries (UNCHS 2002). Urban centers in Latin America, Asia and Africa are expanding rapidly and their populations are estimated to double by URBANIZATION IN AFRICA Throughout Africa, urbanization is increasing. Urban areas have expanded enormously in population and size and there is growing concentration of population in a few large cities especially in the national capitals. In 1950, Africa was the least urbanized continent with only 14.5 percent of the population in urban areas. However, by 1990, 34.5 percent of the population of 749 million was living in urban areas. The UN has projected that if the trends continue, the urban population would increase to 914 million by 2025, or four times the 1990 level. Although urbanization is growing throughout the world, the growth of cities is more rapid in the developing countries especially Africa where annual growth rate is 1.6% compared to 0.8% in the developed countries. In 1950, Africa was the least urbanized continent with only 14.5% of the population in urban areas, but by 1988, about 35% of Africa s population of 749 million people was urban. UN projections indicate that the urban population will increase to 914 million by 2025 or 4 times the 1990 levels. In sub-saharan Africa (SSA), the least urbanized but most rapidly urbanizing part of the world, the United Nations projects that nearly one-half (49%) of the population will be urban by 2025 (UN, 1996). In many African countries, urbanization has resulted in rapid population growth and concentration of people and industries in few urban areas such as Accra (Ghana), Lagos (Nigeria), Monrovia (Liberia), Abidjan (Cote d Ivoire) etc. Urban population growth has been fuelled by massive rural-urban migration from remote towns and villages to large cities and urban centers, in the belief that urban centers provide better job opportunities, social services and wages. URBANIZATION IN SUB-SAHARAN AFRICA In Sub-Saharan Africa, the least but the most rapidly urbanizing part of the world, nearly one third (32 percent) of the population live in few large cities and major economic activities including industry, manufacturing, commerce and employment are concentrated in cities such as Accra (Ghana), Lagos (Nigeria), Monrovia (Liberia), Nairobi (Kenya) etc. The UN estimates that two out of four people would live in urban areas by 2020 and about 49 percent of the population will be urban by 2025 (UN 1996). There will be more than 20 capital cities in Africa that have a population of 10 million people by the year

7 TABLE 1. URBANIZATION IN SUB-SAHARAN AFRICAN REGIONS ( ) Region Sub-Saharan Africa Eastern Africa Middle Africa Southern Africa Western Africa Percent of population in urban areas Source: UN Urbanization Prospects: The 1996 Revision Annex Tables CAUSES OF URBANIZATION The causes of rural-urban migration are many. There are so many people migrating to the urban areas, and they are doing so because the types of activities that ought to be taking place in the countryside to keep the youth in the rural areas do not exist. The main causes of urbanization in Africa include rural-urban migration; high natural rate of increase and urban bias development strategies. (a) Rural-urban migration Movement of people from the rural to the urban areas is the most important cause of urbanization in Africa. Added to this are the predominance of young adults, and more or less equal proportions of males and females whose desire for large families is high. (b) High birth and low mortality rates Africa has the highest fertility and natural rates of increase in population in the world. Data from censuses and surveys suggest levels of total fertility mostly between six and seven children per woman. Population growth has become the highest in the world because of a sustained decline in mortality due to improved medical care and sanitation. Urban bias development strategies Pro-urban development strategies adopted by countries have left urban areas more developed than the rural areas. The greater opportunities cities offered in the urban areas in terms of employment, education, health and other facilities tend to attract the youth to the urban areas. Whilst the urban population is growing rapidly through natural increase (i.e. more births and deaths), immigration or migration from the rural to urban areas is also increasing. In most parts of Africa, rapid flow of migrants from rural to urban areas and rapid urbanization began after most countries gained independence in the 1960s. During the colonial era, migration from rural to urban centres was suppressed by law, in some 7

8 countries to ensure the security and safety of the white population in the cities. After independence, migration from rural to urban areas was seen to offer the hope for employment and a better life. Recently, lack of basic infrastructure and services and deterioration in the economic conditions in the rural areas have accelerated the flow of migrants from rural to urban areas, thus increasing urbanization. It is estimated that under current trends, about two out of three West Africans will live in urban centres by Natural increase is fuelled by improved food supplies, better sanitation, and advances in medical care that reduce the death rates and cause populations to grow both within cities and the peri-urban areas. In Ghana, immigration to cities is the largest source of urban growth and this is caused by push factors that force people out of the rural areas and by pull factors that draw them into the cities and urban areas. People migrate for several reasons and no single factor acts independently to influence prospective migrants final decision to move. For this reason, a unified theory to explain rural-urban migration is unrealistic (Hance, 1970, Kasanga and Avis, 1988). However, at any point in time, in a given location where there is voluntary movement, a particular factor will be more prominent than others. On one hand, political strife, natural disasters, socio-cultural constraints, religious persecution, economic decline and environmental degradation are some of the push factors. For example, Accra experienced net out-migration during the worst of Ghana s economic crisis in the 1980s (Simon, 1999). On the other hand, economic prosperity, improved food supplies, boom and busts can generate migration and pull people from places of decline within and across national boundaries Todaro, 1976). Modern communications especially television that broadcast and show images of luxury and opportunities in the cities draw people to the cities. In Africa the foundation of rapid urbanization was laid by post-colonial development policies with their focus on industrialization in a few urban centres. The post-colonial development policies resulted in high concentration of population, industries supporting infrastructure and services in a few, key urban settlements whose pride of place was founded on their historic position as colonial out-posts. In many countries, migrants move to urban areas mainly in response to better employment and income opportunities. Therefore true determinants of urbanization and spatial concentrations of population are found in the forces that determine the location of employment opportunities, such as the nature and pattern of industrialization, the pace of agricultural development, and the growth of transportation and communication networks. The harsh socio-economic, insecurity of tenure and environmental conditions in the rural areas also push the youth out of agriculture in response, they move to urban areas for non-exiting white collar jobs. At the same time, the several attractions of the city such as better health and educational facilities improved social life and perceived higher white-collar job opportunities, exerted their own pull on the youth to migrate to the cities and urban centres. 8

9 In the last two decades, agriculture has been deteriorating in the arid and semi-arid regions in Africa because of frequent drought indiscriminate bush burning poor producer prices and soil degradation. Lack of land, insecurity of tenure, lack of employment opportunities, basic services and infrastructure in the rural areas such as schools, health facilities, water, electricity etc. often force people, mostly the youth, to migrate to the urban areas where basic services and facilities are available BENEFITS OF URBANIZATION Urbanization leads to economies of scale in provision of water, health, education, electricity and other services. Industries benefit from concentration of suppliers and consumers and allow savings in communications and transport costs. Cities serve as commercial, administrative, and growth centers and are generally places for production and consumption of goods and services. Cities provide big, differentiated labour markets and help to generate new ideas and accelerate the pace of development of technological innovation and dissemination. NEGATIVE IMPACTS OF URBANIZATION Firstly, as urban areas grow, demand for land for housing, agriculture and urban infrastructure increases leading to increased pressure on farmlands, forests and water resources. Secondly, rapid urbanization accelerates desertification and environmental change, leading to water scarcity, soil erosion, and climate change A prosperous urban center provides a number of benefits and contributes to poverty alleviation through the provision of: Markets for agricultural and industrial goods Financial resources Employment opportunities for agricultural and industrial activities Resources and capacities for government and politics Centers for artistic, scientific and technological innovations and of culture and education A wide range of cost-effective services including health and education. THE URBAN CHALLENGE The major challenges to rapid urbanization and population growth include: Inadequate sanitation, air and water pollution Inadequate housing and overcrowding Environmental degradation such as deforestation, soil erosion etc. 9

10 Climate change, food insecurity Competition for water and land Exposure to higher risks of accidents Crime and diseases e.g., HIV/AIDS Poverty and deprivation and natural disasters THE RURAL AREAS AND THE PERI-URBAN INTERFACE Many of the detrimental effects of rapid urbanization occur in the rural and peri-urban areas which serve as sources of food, building materials and fuel wood for urban dwellers while serving as sinks for wastes generated from the urban centers. The critical challenges are water and land use change and land degradation, soil erosion, inadequate potable water supply, congestion, poor housing infrastructure, air pollution, garbage and spread of infectious and parasitic disease. URBAN AGRICULTURE AND FOOD SECURITY Millions of men and women are now farming in cities to improve urban food security. In spite of this, many African countries are food insecure. The food crisis poses a great threat not only to human survival but also to the very ability of Africa to cope with the challenges of rapid urbanization, population growth, globalisation and environmental change in a context of low level of technology and inefficient institutional support. URBAN FARMING SYSTEMS Urban Farming systems include: Intercropped bush fallow food crops Backyard farms or field plots that are owned or rented (e.g. Banana, plantain) Mono crop vegetables under irrigation Specialized valley bottom cropping Livestock and fish farming It is estimated that 25%-100% of urban food demand is through urban horticulture, aquaculture, crop and livestock production. Of particular importance are perishable foods, and vegetables, lettuce, onion and sweet pepper that have ready market in the urban areas. The ready market in the urban areas provides and opportunity for farmers to benefit from short transportation and problems related to storage and preservation between harvest and sale. At the outskirts of the urban centre and along the major roads to the city, women display vegetables for sale to travellers who don t have the time to shop in the markets. 10

11 Figure 3 shows a backyard garden where plantain and banana are the dominant crops. It also shows the importance of tomatoes in urban agriculture. Figure 4 also illustrates the role of women in agriculture, especially marketing of vegetables. FIG.3: BACKYARD FARM AND A VEGETABLE FARMER WEIGHING TOMATOES 11

12 FIG. 4. WOMEN SELLING VEGETABLES AT THE PERI-URBAN INTERFACE IN GHANA LIVESTOCK PRODUCTION AND POULTRY KEEPING The rearing of livestock and keeping of poultry are important economic activities in urban areas. Leaching and droppings from the animals and birds pollute drinking water sources. 12

13 FIG 5. URBAN HORTICULTURAL CROPS AND LIVESTOCK PRODUCTION Urban agriculture has direct linkages with poverty reduction, employment, human health, environment and sustainable development. Animal droppings and domestic wastes are recycled and used as manure to improve soil fertility. Figure 6 shows a pile of poultry manure awaiting collection by farmers. 13

14 FIG. 6 POULTRY MANURE DUMPED AT THE OUTSKIRTS OF THE CITY TO BE COLLECTED BY FARMERS IMPACT OF URBAN AGRICULTURE ON THE ENVIRONMENT AND HUMAN SECURITY There are both positive and negative effects of urbanization in Africa. Current trends of urbanization and ensuing natural resources and environmental degradation have increased people s vulnerability to water scarcity, hunger, disease, poverty and deprivation. As cities expand, those living on the margins or peri -urban interface face new challenges and new opportunities. Rapid urbanization and population growth and their socio-economic and environmental outcomes are illustrated in figure 7 below: 14

15 URBANIZATION Rural Urban Migration High birth rates Low Mortality Rates WATER AND LAND USE HUMAN OUTCOMES * Increased Agricultural and * Food Insecurity Industrial Production * Water-borne illness * Sanitation and waste disposal * Social and Political Instability * Increased Natural resources * Conflicts over land, water and (e.g. water) food * Deforestation * Population displacement * Poverty ENVIRONMENTAL OUTCOMES Depletion and pollution of water Resources. Land degradation Climate change Increased vulnerability to natural Disasters FIG 7. Human and Environmental Outcomes of Rapid Urbanization in Africa 15

16 FERTILIZERS AND AGRO-CHEMICALS As cities expand, those living on the margins or peri -urban interface face new challenges and new opportunities. The increasing use of agricultural fertilizers and pesticides for vegetable and horticultural crop production and improper handling of agro-chemicals affects the health of farmers. Figure 8 shows a farmer applying fertilizer by hand and a woman FIG 8: UTILIZATION OF FERTILIZER AND PESTICIDES IN URBAN AGRICULTURE 16

17 URBAN AGRICULTURE AND HEALTH The urban population is vulnerable to diseases such as malaria. They also face diseases associated with industry and traffic injuries, consumption of infected food. Urbanization exposes the youth to crime, and diseases including HIV/AIDS, often associated with high levels of commercial sex, commonly found at high level in cities. Africa s changing climate as well as increased urban agriculture will affect people s livestyles and health. Related Impacts of Urban Agriculture on Human Health Agro- Liquid waste Solid waste Land chemicals Clean water Injury URBAN GI AGRICULTURAL PRODUCTION Poisoning Malaria Fuel and Animal Liquid waste Food crops products INJURY Transport, Zoonoses Surface Ground Storage, water water Filariasis 17

18 Outdoor air Food Drinking Pollution processing water contamination POISONING INJURY Loss of GI GI wild foods Poisoning Indoor air Street and Pollution domestic food Injury COLD Poisoning ARI Malnutrition GI Malnutrition FIG 9. URBAN AGRICULTURE AND RELATED IMPACTS OF URBAN AGRICULTURE AND HEALTH KEY ARI = Acute respiratory infection COLD = Chronic obstructive lung disease GI = Gastro-intestinal infection RAPID URBANIZATION AND URBAN CLIMATE CHANGE 18

19 Africa s climate is changing. Accelerated by global warming, greenhouse gases including carbon dioxide. The climate is believed to be warmer than it has been in the beginning of the 19 th century. Already, we are increasingly seeing the impact of climate change on natural ecosystems such as increased drought and aridity, floods and accelerated desertification. The rate of climate change will be slowed when people lower energy consumption and promote clean, renewable energy alternatives and undertake tree planting. However, in many countries, construction of urban infrastructure has sealed off land surfaces that were previously functioning as catchments and recharges for local aquifers, thus decreasing water availability and increasing urban climate. DEFORESTATION Urbanization leads to changes in land cover, Rapid urbanization has increased demand for timber and fuel wood, resulting inland degradation, changes in climate and hydrological cycle, and food insecurity. Gathering of fuel wood to meet energy needs of the urban poor impacts negatively on the environment. Figure 10 shows the importance of firewood in meeting the energy needs of poor urban households and the destructive role of fire in agriculture in the urban area. 19

20 FIG.10. FUELWOOD COLLECTION AND ANNUAL BUSH FIRE MENACE These activities have accelerated soil fertility decline, loss of bio-diversity, and leaching of soil nutrients that pollute rivers and streams in the urban and peri-urban areas. COMPETITION FOR WATER SUPPLY Urbanization and population growth contributes to deforestation and changes in land cover that affects water resources. Deforestation alters the hydrological cycle because forests act as water regulators by reducing runoff and soil erosion and by helping to replenish groundwater. Water is life and water shortage affect women and children most. Figure 11 illustrates the role of women and children in water supply. 20

21 FIG. 11. COMMUNITY WATER SUPPLY SYSTEM They also release moisture into the atmosphere to cause rainfall. High water consumption by the urban population has affected water availability for consumption, industrial and agricultural production. DESTRUCTION OF BIODIVERSITY Intensive cultivation of food and horticultural crops as well as vegetables, has resulted in the destruction of biodiversity, watersheds, wetland ecosystems and led to pollution of water resources that serve as drinking water sources. 21

22 INADEQUATE SANITATION Urban areas depend on their surrounding regions to act as both official and unplanned repositories of polluted water resources, sites for refuse tips, sewage treatment, and disposal of domestic and industrial wastes. Inadequate sanitation including poor waste disposal and drainage systems and wastewater discharges from industry, agriculture and domestic use cause surface and groundwater pollution. Figure 12 shows the problem of inadequate waste disposal and exposed drainage system in an urban slum. Fig. 12. WASTE DISPOSAL AND POOR DRAINAGE SYSTEMS OVERCROWDING AND POLLUTION 22

23 Urbanization increases overcrowding and traffic congestion. Inadequate housing and uncontrolled housing development due to weak planning systems lead to the development of slums or shanty settlements. In many African countries environmental pollution control measures are weak and pollution arising from industries and chaotic movement of vehicles is high. Associated with dense city population is noise pollution. Urban problems affect children most leading to diseases and stunted growth of children who are unable to care for themselves. Figure 13 shows the problems of overcrowding in the streets as well as the impact of urban poverty on children. FIG. 13 A CROUDED CITY STREET AND THE EFFECT OF URBAN POVERTY ON CHILDREN 23

24 The insufficiency of services results in deterioration of urban environment in the form of air and water pollution and land degradation that pose serious risks to human health and food security. Congestion and overcrowding results from gigantic traffic jams which occur on all the major roads especially during the rush hours. In Lagos and Accra, for example, the urban areas suffer from inadequate housing and from decay of urban infrastructure. Urbanization has led to lawlessness and uncontrolled urban growth and the development of slums. These areas often lack basic needs for living such as potable water, shelter. The health risks were high. POOR ACCESSIBILITY Associated with rapid population growth and urban sprawl is the problem of traffic congestion and air pollution. Long traffic queues do not only retard businesses but also constitute an important source of pollution and a disincentive to investment and job creation. STREET HAWKING The issue of street hawking is increasing in the urban areas. Hawkers, who sell all sorts of goods including toilet rolls, handkerchiefs, dogchains, bread, fruits etc, are not mindful of sanitation and the environment. Apart from creating congestion on the major roads, these hawkers litter the streets with wrappers, thus making the streets untidy. The hawkers are also exposed to various health risks. RECOMMENDATIONS A strategy to reduce environmental damage caused by rapid urban urbanization is to plan urban areas in such a way that they can provide a real sense of community, with good sanitation, adequate housing, health care and education facilities. The focus of today s cities must be towards better urban development. Government policies to urban unemployment and environmental problems must be based on knowledge of who comes to the city and how they cause and contribute to the problems in the city. Recycling of domestic and industrial wastes should be promoted to improve degraded soils and urban agriculture. Ensure effective urban infrastructure planning and enforce planning laws and regulations Develop the rural areas to curb rural-urban migration Intensify family planning and population control programs Recycle domestic and industrial wastes and improve urban sanitation Encourage industries to locate in the rural areas Promote HIV/AIDS education Improve sustainable urban agriculture Promote sustainable co-management of urban natural resources 24

25 CONCLUSION Although Africa has become synonymous with rapid urbanization, it is neither a crisis nor a tragedy. Urbanization has created a host of new opportunities with new and ill-understood environmental, food and human security problems. Although urbanization is associated with unemployment, air and water pollution, congestion, overcrowding, social disturbances, crime, ethnic conflicts, environmental degradation, HIV/AIDS etc., however, it provides opportunities for growth and development of markets for consumer goods and a source human capital for managing natural resources. The focus on cities must move decidedly towards better planning and management with past failures giving way to more appropriate policies and practices. Proper land use planning, urban environmental monitoring and family planning are required to solve the problems of urbanization in Africa 25