Oh Shanghai! China city tops flood vulnerability index

A new study, using a broad range of criteria and data, suggests Shanghai is the world's most vulnerable major city to flooding. In spite of gleaming skyscrapers and state-of-the-art mass transit systems, China's most flamboyant city surpasses other Asian coastal conurbations as being the most at risk from the rising sea levels driven by changing climate.

The new research, A flood vulnerability index for coastal cities and its use in assessing climate change impacts, published in the journal, Natural Hazards, looks not just at cities’ physical characteristics but also at their socio-economic and institutional systems, to assess the impact of flooding.

Written without hyperbole, the report from researchers from the UK and the Netherlands shows Shanghai to be the most vulnerable in three of the four evaluation criteria. The Chinese city was rated as most vulnerable in terms of its hydro-geological exposure, societal aspects and, perhaps surprisingly, the politico-administrative component which covers institutional organizations involved in the flood management process.

In the past year, there have been deluge of reports warning of Asia's vulnerability to natural disasters with both Maplecroft and the Asian Development Bank earlier this month highlighting the risks faced by the region.

In June two reports warned of the impact of rising sea levels in the region. A study published in the journal Global Change Biology projected devastation among flora and fauna across Southeast Asia, southern China and the eastern Pacific. And an updated report from China's State Oceanic Administration warned that flooding would affect three percent of the country's population living on 87,000 square km of coastal lowlands by 2050.

In March a World Bank report warned that the rapid growth of cities across the developing world has resulted in urban areas overtaking rural communities as being the most vulnerable to wide scale flooding, with the slums of Asian cities especially vulnerable.

The new Natural Hazards study offers a more substantive analysis of the impact of exposure to extreme weather conditions and rising sea-levels. The researchers created an index which, they hope, can be used in differing scenarios to make policy-makers more aware of their cities’ vulnerabilities and, along with water authorities, define what measures should be taken.

The Coastal City Flood Vulnerability Index (CCFVI) uses 19 component factors which include economic and social ones, such as how much attention is given by local or national governments to protect people, business and property through investing in various forms of preventative and emergency resilience.

In their paper the researchers focused on nine large cities in low-lying, deltaic environments with soft sedimentary coasts (estuaries, lagoons, mangroves, dunes, beaches). These cities experience both the influence of river discharge and of the sea and they are, by consequence, very vulnerable to impacts of climate change.

When examining the hydro-geological exposure, for example, Shanghai was found to be the most at risk to coastal floods, mainly due to the length of its coastline and the high volume of river discharge.

Unsurprisingly, Manila was next on the list for the same criteria, largely due to its exposure to tropical cyclones and low-lying terrain. During Typhoon Ketsana in 2009, for example, flood waters reached nearly seven meters above sea levels in some parts of the city.

Dhaka and Calcutta come next largely because of their storm surge, coast line length and river discharge. Other cities covered in the study, in order of vulnerability, were Rotterdam, Buenos Aires, Marseille, Osaka and Casablanca.