The Red Cross is warning nearly one billion people living in slums in the developing world are vulnerable to disasters.
The Red Cross says natural disasters such as floods and earthquakes hit poor countries the hardest because they do not have the infrastructure to cope.
"The earthquake in Haiti is a stark reminder that urbanization comes at a cost," said Graham Saunders from the International Federation of Red Cross.
Haiti's capital Port-au-Prince has a population of two million. Saunders says it will take a decade to rebuild the city after a catastrophic earthquake hit the country in January.
He says a major problem is poorly constructed buildings, which cannot withstand natural disasters. But the problem goes further, he says. Poorly planned urban areas and bad roads can make rescue more difficult if not impossible when a natural disaster happens.
What is more, he says, rapid urbanization can lead to a wide range of social and economic problems. For example if health systems are not in place disease can spread rapidly.
He says a good example of that is the Kibera slum in Nairobi.
"In some ways it is quite start that something like 17 percent of the population have diabetes or actually blood deficiencies, which of course is not representative of the rest of the population," added Sauders.
Saunders says there is a tendency for issues such as health or city planning to be looked at individually, but he says that may not be the most effective system.
"In many ways these issues interlink and rather than struggling along addressing these issues, trying to tick them off solely, it is a question of recognizing that in some ways risk needs to be managed a little bit more holistically," Saunders explained.
Saunders says despite popular perceptions, Africa has the largest urban population in the world. The report says Africa has an urban population of around 412 million.
According to the report, around 50,000 people were killed every year between 2000 and 2008 in a seismic event such an earthquake or a tsunami. During the same period, floods affected almost 100 million people.