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Using high resolution satellite data for the identification of urban natural disaster risk

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Urban disaster risk

Natural disasters impose a significant cost on developing countries. A recent global risk assessment estimates average annual economic losses due to cyclones to be almost 40 billion USD and from earthquakes 22 billion USD (ISDR 2009). Mortality due to these disasters is also significant. Almost 250,000 people were killed in earthquakes in the ten years between 1999 and 2008, more than 90% in just five events. A single event since then, the 2010 earthquake in Haiti caused more than 200,000 deaths. Annually, almost 70,000 people are killed by natural disasters annually—the vast majority in low and middle income countries and most in a small number of mega-disasters.

The proportion of damages that occur in urban areas is not known but very likely significant. Many cities are located in hazard prone areas that also provide some other natural advantage—accessibility near rivers and shorelines or fertile soils near volcanic areas. Fast growing cities are densely packed, so if a hazard event occurs, more people will be affected and indirect impacts, such as epidemics following disruption of water supply, spread faster. This density also causes land to be scarce and therefore expensive. This causes poor migrants to locate in under-serviced informal settlements on the least desirable urban land—often areas subject to flooding or landslides. Dwelling units in urban areas are also larger and constructed with more solid materials than in rural areas. They can often withstand greater force, but when they fail because of substandard building practices, loss of life and damages are larger. A large share of the loss of life in recent earthquakes in Sichuan (2008) and Kashmir (2005) has been in the collapse of multi-floor buildings.

Rapid urbanization in many parts of the world also means that the number of cities and the urban population in areas where natural hazards occur will be growing for some time to come. Recent estimates suggest that the population in large cities exposed to tropical cyclones increases from 310 to 680 million between 2000 and 2050, and exposure to severe earthquakes from 370 million to 870 million (World Bank 2010, Lall and Deichmann 2009). Reducing disaster risk in urban areas is therefore a pressing challenge for city, state and national governments.