Flood warning

More than three times the number of people around the world could be exposed to coastal flooding by 2070, largely because of climate change, a new report argues. With urban development along coasts increasing, an estimated 150 million people–up from 40 million people today–could be exposed to a one in 100 years coastal flood event.
The estimated financial impact of such an event would rise to US$35 trillion, up from $3 trillion today.

The OECD report, co-authored with experts from the University of Southampton, Risk Management Solutions, Météo-France, and the Centre International de Recherche sur l’Environnement et le Développement, is the first in a series that will focus specifically on the impacts of climate change on cities.

Looking at over 130 port cities around the world, it found that around half of the total population exposed to coastal flooding is contained in just 10 cities. By 2070, an estimated eight out of ten of these cities will be in Asia, as unprecedented growth and development of Asian megacities increase the risks of global flooding. Mumbai is currently the most vulnerable city. Yet, by 2070 Calcutta will surpass Mumbai as the city’s population exposed to coastal flooding increases sevenfold to more than 14 million people. Calcutta and Mumbai will be closely followed by other Asian cities, such as Dhaka, Guangzhou, Ho Chi Minh City and Rangoon.

That ranking changes when the cities with the highest value of property and infrastructure are considered. Those cities whose assets are exposed to coastal flooding are primarily in developed countries. So while Miami is expected to rank ninth in terms of city populations most vulnerable to coastal flooding, by 2070 it is estimated to come in highest in terms of assets, whose exposure to flooding will surge from $400 billion to $3.5 trillion. Miami is followed by other cities such as New York and Tokyo, as well as major cities in developing countries, such as Calcutta, Shanghai and Bangkok.

How can policymakers respond? Sure enough, mitigation strategies can slow and limit the exacerbating effects of climate change on coastal flood risk, but already an estimated consequence of climate change includes a sea level rise of half a metre by 2070, due in part to polar melting. And since effective coastal defences can take 30 years to put in place, policies to encourage people to adapt will have to be quickly implemented today if they are to make a difference tomorrow. So, while policies to fight against climate change should be encouraged, more focus should be placed on adaptation strategies to new climate realities, such as better land use planning and selective relocation away from exposed city areas. SK

See Environment Working Paper No. 1, “Ranking Port Cities with High Exposure and Vulnerability to Climate Extremes”, 2007, at www.oecd.org/env/workingpapers

See also “Don’t forget the coastal waters!” in OECD Observer No. 254, March, 2006.

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