The State of the World's Cities Report 2006/7: Urban and slum trends in the 21st century.

• Author: Moreno, Eduardo Lopez

Sometimes it takes just one human being to tip the scales and change the course of history. In 2007, that human being will either move to or be born in a city, and demographers watching urban trends will mark it as the moment when the world entered a new urban millennium in which the majority of its people will live in cities. It will also see the number of slum dwellers cross the one-billion mark, when one in every three city residents will live in inadequate housing, with no or few basic services.

Three important trends characterize the urbanization process in this new urban era. Firstly, the biggest cities will be found mainly in the developing world. "Metacities"--the massive conurbations of more than 20 million people above and beyond the scale of megacities--are gaining ground in Asia, Latin America and Africa. Home to only 4 per cent of the global population, most of them have grown at the relatively slow rate of about 1.5 per cent annually. However, the sheer size of these urban agglomerations points to the growth of city-regions, as well as to "metropolitarization", which calls for more polycentric forms of urban governance and management and stronger inter-municipal relations. The scale of environmental impact of metacities and megacities on hinterlands is also significant and is likely to be a cause for concern in the coming decades.

Secondly, despite the emergence of metacities, the majority of urban migrants will move to small towns and cities of less than 1 million inhabitants. More than half of the global urban population lives in cities of less than 500,000 inhabitants, and almost one fifth in cities of between 1 million and 5 million inhabitants--these intermediate places are predicted to grow at a faster rate. Natural population increase, rather than migration, is becoming a significant contributor to urban growth in many regions, as is reclassification of rural into urban areas. However, the relative absence of infrastructure, such as roads, water supply and communication facilities, makes many cities less competitive and leads to a lower quality of life for their citizens.

Thirdly, cities of the developing world will absorb 95 per cent of urban growth in the next two decades, and by 2030 will be home to almost 4 billion people, or 80 per cent of the world's urban population. After 2015, rural population will begin to shrink as urban growth becomes more intense in cities of Asia and Africa, which are set to host in 2030 the largest urban populations, 2.66 billion and 748 million, respectively. Poverty and inequality will characterize many developing-world cities, and urban growth will become virtually synonymous with slum formation in some regions. Asia is already home to more than half of the global slum population (581 million), followed by sub-Saharan Africa (199 million), which has both the highest annual urban growth rate (4.58 per cent) and the highest slum growth rate (4.53 per cent), and Latin America and the Caribbean (134 million).

The continued threat of conflict in several African countries is a significant contributing factor in the proliferation of slums in urban areas. The prolonged crisis in southern Sudan, for instance, has led to the mass exodus of rural communities to the capital Khartoum, which accommodated almost half of the more than 6 million internally displaced persons during the late 1990s. These trends will most likely continue to concern policymakers in the developing world as they confront the reality of growing inequality and poverty in their cities.

However, urbanization can also be a positive force for human development. Highly urbanized countries tend to have higher incomes, more stable economies, stronger institutions and are better able to withstand the volatility of the global economy. In both developed and developing countries, cities generate a disproportionate share of gross domestic product and provide extensive opportunities for employment and investment. Evidence suggests that despite their enormous potential to bring about prosperity, the wealth they generate does not automatically lead to poverty reduction. On the contrary, inequalities between the rich and the poor in many cities have grown, as have the size and proportion of slum populations.

Although poverty remains a primarily rural phenomenon, it is quickly becoming a severe, pervasive and largely unacknowledged feature of urban life. Large sections of the urban population are suffering from extreme levels of deprivation. The UN Human Settlements Programme (UN-HABITAT) analyses show that incidence of disease and mortality is much higher in slums than in non-slum urban areas and in some cases, for example HIV prevalence, is equal to or even higher than in rural areas. Inequality in access to services, housing, land, education, health care and employment opportunities within cities have socio-economic, environmental and political repercussions, including rising violence, urban unrest, environmental degradation and...