Major coastal cities around the world face a grim possibility of serious flooding with Shanghai being the most vulnerable of all cities. A new study of nine coastal cities around the world suggests that Kolkata in India could experience coastal flooding as the city is built on river delta.
These finding are based on a new method to calculate the flood vulnerability of cities, developed by a team of researchers from the Netherlands and the University of Leeds. The work is published in the latest edition of the journal Natural Hazards .
The index does not just look at the likelihood of a city’s exposure to a major ‘once in a hundred years’ flood but includes social and economic factors in their calculations. The index incorporates 19 components, including measures of the level of economic activity in a city, its speed of recovery, and social issues such as the number of flood shelters, the awareness of people about flood risks and the number of disabled people in the population. Several index components also look at the level of administrative involvement in flood management.
The researchers used their index to analyse the vulnerability to coastal flooding of nine cities built on river deltas: Casablanca (Morocco), Kolkata (India), Dhaka (Bangladesh), Buenos Aires (Argentina), Osaka (Japan), Shanghai (China), Manila (Philippines), Marseille (France) and Rotterdam (Netherland).
The results of the analysis reveal that the highly prosperous megapolis of Shanghai is more vulnerable than much poorer cities such as Dhaka. “Vulnerability is a complex issue,” explains Professor Nigel Wright, who led the team from the University of Leeds. “It is not just about your exposure to flooding, but the effect it actually has on communities and business and how much a major flood disrupts economic activity. Our index looks at how cities are prepared for the worst – for example, do they have flood defences, do they have buildings that are easy to clean up and repair after the flood? It is important to know how quickly a city can recover from a major flood.”
Shanghai is particularly vulnerable because it is exposed to powerful storm surges and the land is subsiding as sea levels rise. Moreover, although a large population lives along the coast in flood-prone areas, the city is poorly prepared, with little resilience to a major flood and insufficient flood shelters for victims. “A one-in-100 years flood in Shanghai would lead to widespread damage, with serious consequences for the city, across China and, through wider economic links, for the whole world,” Professor Wright says.
The vulnerability index also revealed that Dhaka, which sits just metres above current sea levels, is regularly hit by tropical cyclones and floods, yet it has few defences in place and little resilience. Manila and Kolkata are highly vulnerable mainly because of their large populations and degree of exposure to storms.
The European cities of Marseille and Rotterdam are also exposed to flood risks, with violent storms, high river levels and significant low-lying areas. But the cities are least vulnerable with good flood management infrastructure and tight building regulations for flood-prone areas. “When a big flood hits you will still get flooding,” says Professor Wright, “but these European cities will bounce back quickly.”
