By Sara Sreberny-Mohammadi
BBC News Online in Barcelona
The mass worldwide migration of people from rural to urban centres is causing massive damage to both locations.
Migration increases the divide between cities and countryside
People are flocking to the world's major cities in larger numbers than ever before, because of factors such as war, unemployment, and a lack of security.
But in many cases, their arrival is exacerbating a divide between the countryside and urban centres, the World Urban Forum has been told.
"We do not address the problems in the countryside," argued Zenaida Delica, of the Centre for Disaster Preparation in the Philippines.
"We end up with overloaded cities."
Cities were attractive to many in rural areas, not least because they were seen as relatively "secure" in comparison with rural communities, Ms Delica said.
In some countries, rural communities were often caught in the crossfire between rebel and government-backed groups, she added.
Adding to risks
The Forum was told how crippling rural unemployment could add to the problems. Developments in agriculture have meant farmers are able to gather their crops using much less labour.
People are therefore attracted to urban living as cities hold incredible potential as engines of growth and social development.
Yet the majority do not find many improvements. Most of the world's poor live in densely populated squatter settlements and lack many of the basics of human survival.
"People who move, for a time at least, are living as rural people in an urban setting," said Kenneth Westgate, of the UN Development Programme (UNDP). "That adds to their risk."
Often on the outskirts of cities, such settlements occupy wasteland, which is susceptible to landslides, flooding and other natural hazards.
The Forum was told that the developing world was often caught up in a disaster and re-building cycle, in which devastation might be repaired but its underlying causes were overlooked.
With metropolitan cities of over 10 million people - so called "mega-cities" - on the increase, addressing prevention, response and reconstruction of the effects of natural risks was necessary, delegates said.
In 1950, one-third of the world's people lived in cities. Today this has risen to one-half and by 2050, it will grow to two-thirds or six billion people.
Population density not only increased the vulnerability of urban centres but magnified the impact of natural disasters, delegates heard.