Evidence from cities in Africa, Asia and Latin America, shows that the expansion of informal settlements is closely associated with the rapid increase in weather-related disaster reports in urban areas. Flood loss reports in the city of Cali, Colombia are shown in the map for each decade since the 1950s. The centrifugal expansion of reported floods has mirrored the expansion of informal settlements in the city.
Urbanization per se tends to increase the intensity of run-off during storms and heavy rains. Instead of being absorbed into the ground, greater volumes of rainwater are channelled into drains, culverts and streams. Informal settlements typically occupy land deemed unsuitable for residential or commercial use, located in low lying flood prone areas, on landslide prone hillsides or in ravines, exposing people to hazard. Houses are built and modified without reference to hazard resistant building standards. In many cities there has been an underinvestment in building drains and in maintaining those that exist, particularly in informal settlements. Many floods are caused as much by deficient or non-existent drainage as by the intensity of rainfall.
Sunday, 17 May 2009
Global Disaster Map
A new UN study released today compares different types of natural disasters against population and economic trends to highligh areas of high risk of death. Among the fascinating results, includes the commentary on how increased urbanisation is putting many poor countries at crisis, as the countries fail to plan cities properly :