Governmental policies aimed at retarding urban growth and depriving the poor of benefits and services increase poverty and environmental degradation, creating serious long-term problems that could be avoided by enlightened planning, according to a new United Nations study.

The study, published today by the United Nations Population Fund (UNFPA) and the International Institute for Environment and Development, examined Brazil, whose urban growth has been considerably more rapid than the countries in Europe and North America.

At present, Brazil's urban centres represent 80 per cent of the country's population – up from 36 per cent in 1950. But while cities now provide 90 per cent of the country's wealth, more than a quarter of its urban citizens are below the poverty line, and one in 15 lives in extreme poverty.

Rather than addressing social inequalities and planning for urban growth, Brazil had adopted policies that discriminated against urban settlement by poor people, according to the study.

As a result, millions of people are excluded from key services and other benefits of urban life, while facing immense social, economic and environmental challenges – such as crime, pollution, unsafe housing and preventable diseases.

The co-authors of the study – George Martine, a former UNFPA staff member and past president of the Brazilian Association of Population Studies, and Gordon McGranahan, of the International Institute for Environment and Development – said it has lessons for other developing nations.

"The story of Brazil's urban growth shows how deep-rooted inequalities have combined with negative policy stances to generate many of the social and environmental problems that still plague Brazilian society," Mr. Martine said.

"Policymakers in Africa and Asia should embrace and plan for urban growth, so they can take full advantage of its potential to contribute to development, rather than vainly attempting to prevent it as Brazil did," he added.

"A ‘business-as-usual' approach that simply reacts to urban growth will be utterly inadequate," said Mr. McGranahan. "To minimize the negative impacts of rapid urban growth, developing countries can learn from Brazil's experiences and, especially, its mistakes."

According to the latest projections, Africa's urban population is expected to grow by 936 million in the first half of this century while Asian cities will grow by more than 2 billion.

The critical first step, the study concluded, is for policymakers to recognize the rights of poor people to live in cities and share in the benefits of urban life. The next is to plan ahead for their land and housing needs within a constantly updated vision of sustainable land use. This not only improves the lives of the poor, but enables the city to become prosperous and habitable for all.

"Urbanization and massive urban growth in developing countries loom as some of the most critical determinants of economic, social and ecological well-being in the 21st century," said Mr. Martine. "Policymakers can learn much from the experience of Latin American countries — and especially Brazil — that have already gone through an early urban transition."