Every second, someone in the world moves into a slum. Over the next 30 years, the world's slum population will, on average, increase by 100,000 each day. Globally, we are seeing a shift from rural areas to cities and, before the year is out, a higher proportion of people will be living in cities than ever before.

Jonathan Watts's article about the growth of a megalopolis in China rightly illustrates some of the startling effects of rapid urbanization (Invisible city, March 15). Watts's picture of a teeming city, smothered in dense pollution and crowded with tower blocks and shopping malls incongruously overlooking slum huts mirrors what I saw on a recent trip to Dhaka, in Bangladesh - and what I have seen in many cities around the world, from Luanda to Mumbai, and Puerto Suarez in Bolivia.

But there is a deeper reality that Watts does not report: in these rapidly growing cities, the proportion of people living in poverty grows at the greatest rate. The population trend to urbanization is important not just because of the numbers, but because of governments' inability to deal with its rate of growth, and this has an impact on every other aspect of life for the poor.

Overcrowding is the most visible problem, but the sheer number of people is just the beginning. In slums across Asia, such as in Mumbai or Dhaka, around 1,000 people live together in each acre of land, without proper sanitation. The result is a massive amount of human and solid waste that even the most willing government would struggle to deal with. The atrocious conditions cause sickness, so people can't work or go to school. Often people cannot find, or hold on to, jobs; and barely anyone has security of land tenure. The narrow lanes between the one-room wooden shacks stop ambulances and fire engines from getting through; people are effectively living in a tinderbox waiting to be set alight.

In Lima, because the government makes no other land available, thousands of people build their homes on top of each other on enormous mountains of gravel and rock. In one of the world's most earthquake-prone zones, this is a disaster waiting to happen; one small tremor would send thousands of homes tumbling down to the sea. Africa is the most rapidly urbanizing continent, and in Kumasi, Ghana, because of a lack of proper sanitation, people in slums use a method known as "flying toilets" - essentially, disposing of their waste in plastic bags and discarding them in the streets. With waste collections irregular, it can stay there for months.

We know from our work in cities around the world that the massive impact of rapid urbanization can only be dealt with when we address the disenfranchisement of the urban poor and generate the political will from city leaders to put resources into poor areas.

Over the past decade, poverty in cities has grown into one of the biggest issues we have to face. People in many slums are treated as though they have no rights to education, to clean water, or to fight eviction. But those rights are theirs. And, as their numbers grow, so too does the need for urgent solutions.

Jennifer Rowell is the urban adviser for Care International.

© 2006 Guardian Newspapers Limited

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