Five of the world’s top 10 cities most at risk of flooding due to climate change are in the United States. Miami, Florida is built right at sea level has the greatest attached cost then New York, New Orleans, Los Angeles, Tampa and Boston in the USA with Guangzhou & Shenzen in China, Mumbai in India, Nagoya & Osaka in Japan following.
The World Bank calculates that the costs of flood damage could rise to $1 trillion a year if 136 coastal cities do not adapt.
The Organization for Economic Cooperation and Development (OECD) forecasts that average global flood losses will multiply from $6 billion per city in 2005 to $52 billion a year by 2050 with just social-economic factors, such as increasing population and property values, taken into account.
Some of the cities where flood risk will increase the most in the coming years are not the cities where the risk is particularly high today, the study found.
The leading cities with the greatest increase in risk are: Alexandria – Egypt, Barranquilla – Colombia, Naples – Italy, Sapporo – Japan and Santo Domingo – Dominican Republic.
The research is part of an on-going OECD project to explore the policy implications of flood risks due to climate change and economic development. This study builds on past OECD work which ranked global port cities on the basis of current and future exposure, where exposure is the maximum number of people or assets that could be affected by a flood.
To estimate the impact of future climate change the study assumes that mean sea level, including contributions from melting ice sheets, will rise between 0.2 meters and 0.4 meters (7.8 inches to 15.7 inches) by 2050. This would mean that the City of Los Angeles would lose $100Billion in coastal property and would need 4M high sea walls.
Inaction is not an option as it could lead to losses in excess of US$1 trillion. Therefore, coastal cities will have to improve their flood management, including better defences, at a cost estimated around US$50 billion per year for 136 cities. To help cities deal with disasters when they do hit, the study advises policy makers to consider early warning systems, evacuation planning, more resilient infrastructure and financial support to rebuild economies.