Floods may cost cities $50 billion by 2050

Rapid population growth, climate change, and economic growth could lead to a huge increase in the risk of floods in cities near the coast over the next forty years, according to a recent article, titled ‘Future Flood Losses in Major Coastal Cities‘, published in the journal Nature Climate Change.

The Organization for Economic Co-operation and Development (OECD) is carrying out a project evaluating policy implications of flood risks caused by climate and economic changes.

The OECD has ranked cities (according to population) that would be affected by a flood.

In total, the authors predict that the future cost of flooding could increase from US$6 billion to US$52 billion by 2050 among the 136  largest coastal cities.

The United States and China are at the greatest risk of coastal flooding, because of their high wealth and poor protection level.

According to the OECD, the cities at highest risk include:

  • Guangzhou, China
  • Miami, USA
  • New York, USA
  • New Orleans, USA
  • Mumbai, India
  • Nagoya, Japan
  • Tampa-St. Petersburg, USA
  • Boston, USA
  • Shenzen, China
  • Osaka-Kobe, Japan
  • Vancouver, Canada

Just the cities of Miami, New York, New Orleans, and Guangzhou account for 43 percent of all flood losses among the 136 cities as of 2005.

Calculating the cost of floods

The most common way of assessing risk is by calculating total cost of losses in dollars.

There is also an alternative way of assessing the risk – by calculating the annual losses as a percentage of a city’s wealth. This means of assessing risk puts the following cities at greatest risk:

  • Guangzhou, China
  • Guayaquil, Ecuador
  • Ho Chi Minh City, Vietnam
  • Abidjan, Ivory Coast

The study assumes that sea-levels will rise 0.2-0.4 meters by 2050 because of melting ice sheets. One quarter of all the 136 cities are exposed to sea-level change.

The study also found that despite flood defenses in some of these major cities, just a slight rise in sea-level could cause devastating losses.

Not acting could lead to more than $US 1 trillion in losses

Therefore the cities need to improve their flood management, which experts estimate will cost around US$50 billion per year for the 136 cities.

Robert Nicholls, Professor of Coastal Engineering at the University of Southampton, England, and co-author of the study, said:

“This work shows that flood risk is rising in coastal cities globally due to a range of factors, including sea-level rise. Hence there is a pressing need to start planning how to manage flood risk now.”

According to Dr Stephane Hallegatte, from the World Bank and lead author of the study:

“There is a limit to what can be achieved with hard protection: populations and assets will remain vulnerable to defense failures or to exceptional events that exceed the protection design.”

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