A study this year, led by the Organisation for Economic Co-operation and Development, shows that among China's cities, Guangzhou faces the highest risk - in terms of its population and assets - from flooding, followed by Shanghai, Tianjin , Ningbo and Qingdao . Hong Kong ranks ninth in terms of the amount of assets exposed to potential coastal flooding, ahead of Ningbo and Qingdao.
This should not surprise us because these are the country's main coastal cities and ports. However, it is sobering to juxtapose populations and assets at risk. Located in delta areas, these cities have a higher flood risk as a result of their tendency to be at lower elevations. They also experience significant subsidence due, in part, to overdevelopment.
About 2.7 million people in Guangzhou are exposed to the risk of flooding; the figure is about 2.5 million in Shanghai and almost 1 million in Tianjin. Guangzhou is second in the world behind Mumbai in terms of population at risk from floods; Shanghai is third and Tianjin seventh. In terms of assets at risk, they are ranked ninth, 10th and 18th, with Hong Kong 15th in the world.
Almost US$85 billion of Guangzhou's assets are at risk from flooding. 'Assets' in this case refers to physical things such as buildings, and transport and utility infrastructure. US$72 billion of Shanghai's assets are at risk and for Tianjin the figure is US$30 billion. US$36 billion of Hong Kong's assets are at risk.
Cities with more assets at risk include Miami, New York, New Orleans, Kobe, Tokyo, Amsterdam, Rotterdam and Nagoya.
By 2070, all these cities will face a much higher exposure to risk. With climate change and subsidence, rapidly growing coastal cities face serious threats from storms, storm surge and sea-level rises. This underscores the need to integrate climate-change factors into both national coastal flood-risk management and urban development strategies. Given the heavy concentration of people and assets in the world's main port cities, and the importance of global trade, failure to develop effective strategies would have local, national and perhaps even wider economic consequences.