Floods threaten millions of lives unless defences are improved

Guardian: Governments must begin major flood defence projects now to prevent millions of lives being lost in coastal floods caused by climate change, say scientists who have produced the first detailed projections of which cities are most at risk. The researchers predict that in 2070 Miami will be the city most exposed to flood risk globally in terms of the value of assets that could be destroyed. Miami is followed by Guangzhou in China, New York, Kolkata in India and Shanghai, in descending order of risk. London is 27th on the list.

The 2070 list is very different from the equivalent ranking for current flood exposure due to rapid economic development in Asian countries. Today's top 10 contains cities from just three developed countries: the US, Japan and the Netherlands.

"The objective really was to try and pinpoint which cities are potentially most vulnerable to climate change and where mitigation efforts should be focused," said Dr Celine Herweijer from the consultancy firm Risk Management Solutions, who was part of the team that compiled the study. "Adaptation is critical. It shouldn't be sidelined," added Herweijer. "[We should] not wait for another New Orleans."

The report was commissioned by the OECD and will be presented next week at the UN's climate change summit in Bali. The team, which included researchers at Southampton University, focused on the 136 port cites around the world with more than one million inhabitants.

It analysed the impact of the kind of storm surge that happens once every 100 years and assumed there were no flood defences in place. Herweijer said there is no reliable database of flood defences for all the cities and that even where they exist they can fail, as happened when Hurricane Katrina hit New Orleans in 2005. The analysis gave each city a ranking of exposure based on either the value of assets that would be destroyed or the number of people affected.

The team then revised their predictions for the situation in 2070. This involved incorporating a half metre of sea-level rise - a fairly conservative estimate - and changes in wind strength and patterns due to climate change. They also factored in projected economic growth and both natural and human-induced subsidence.

The new ranking suggests that Asian cities in particular will be much more exposed to property damage on a massive scale. The value of Asian assets in the firing line from a one-in-100-year flood in 2070 will be 18 times greater than now, and 13 of the top 20 cities that the team predicts are most at risk are in China, India, Japan, Thailand and Vietnam.

…"Even assuming that protection levels will be high in future, the large exposure in terms of population and assets is likely to translate into regular city-scale disasters at global scale," the authors write in the report. They say governments must plan for what happens if flood defences do fail - for example disaster response strategies as well as recovery and reconstruction.

Click here to view the report (pdf, download time >1 minute)