The extent of people’s vulnerability is affected by far more than whether their locality floods. Old people are more vulnerable than young people; more affluent people are better able to take evasive action; more educated people are better able to assimilate the information they receive.
Professor Nigel Wright
A team from the University of Leeds and collaborators from the Netherlands have developed a new index for ranking flood vulnerability. Appearing in the latest edition of the journal Natural Hazards
, the study that has been carried out focuses on nine major coastal cities around the world.
The research was funded by the Government of the Netherlands and its results, perhaps surprisingly, show that prosperous cities such as Shanghai could be more vulnerable to the effects of one-in-100 year floods than less economically well-off cities such as Dhaka.
Professor Nigel Wright, who led the University of Leeds researchers, spoke to ScienceOmega.com
to clarify some of the complex issues involved in producing this flood risk ranking system.
The index developed by Professor Wright and his colleagues builds on previous work in the field by incorporating an analysis of many factors besides the probability of a major ‘once in a hundred years’ flood occurring, as he explained.
"Other indices have been developed for water poverty, climate change vulnerability, and so on. This one is specifically for flooding and includes not only physical factors, but also social, economic and governmental factors."
19 different factors were considered in all, taking into account the number of flood shelters, the number of disabled citizens in the population, and levels of administrative involvement in managing flood situations, for example. Each of these components is essential to gain a more complete picture of the effect an extreme weather event like a flood will have on a city, the communities and businesses within it.
"The extent of people’s vulnerability is affected by far more than whether their locality floods. Old people are more vulnerable than young people; more affluent people are better able to take evasive action; more educated people are better able to assimilate the information they receive."
Each built on a river delta, there were nine major cities which formed the focus of the analysis: Buenos Aires (Argentina), Calcutta (India), Casablanca (Morocco), Dhaka (Bangladesh), Manila (Philippines), Marseille (France), Osaka (Japan), Rotterdam (the Netherlands), and Shanghai (China). They found that the flood-readiness of the different cities varied in a number of ways.
"Cities fall into three broad categories," Professor Wright said. "There are those that have significant economic output that is well-protected, those that have very little economic output which are not well-protected, and those that are newly developed who have significant economic output that is not yet adequately protected."
Shanghai was the most vulnerable of the cities studied not only because of it’s exposed position in terms of storm surges and land subsidence, but because levels of preparation are relatively poor and a large proportion of the population lives in high-risk areas prone to flooding. Dhaka is also vulnerable, as it is regularly hit by tropical cyclones, sits just a few metres above sea level, and has very little resilience to flooding.
According to Professor Wright, there are a number of areas that need to be addressed in order for the most vulnerable cities on the list to improve their chances of recovering quickly and effectively in case of flood.
"They need a combination of investment in hard and soft defences, increased focus from local and national government, and increased awareness amongst the population of the risks and the actions that individuals can take to reduce their vulnerability," he stated.
Hard defences include physical barriers such as walls and retention basins, while soft defences are measures like insurance, evacuation and warning systems. European cities including Marseilles and Rotterdam are also frequently exposed to violent storms and their risk of flood is exacerbated by low-lying ground and often high river levels. However, their infrastructure is much stronger in terms of flood management and building regulations, for example, which means they are able to recover much more quickly.
Although the index cannot give an idea of the knock-on effects for the rest of the world if an economically powerful city such as Shanghai were to suffer extreme flooding, it can, Professor Wright said, highlight ‘hotspots’ where more detailed investigation is necessary. This will only become more important as the vulnerability of all locations rises with the predicted sea level rise over the next 100 years.