The huge economical cost of coastal flooding in 2050

The effects of climate change are enough now-a-days to start assess the economical cost it will cause to humankind in the future.

Climate change, together with population growth in some areas of the world and economical growth, could lead to a big increase of flooding risk in big coastal cities (up to nine times today's risk by 2050).

A paper published in August 2013 in Nature (Hallegate et al. 2013) titled "Future flood losses in major coastal cities" has estimated this cost and is part of a bigger work carried out by the OECD (Organisation for Economic Co-operation and Development) in order to assess flooding risk (particularly due to storms) as a consequence of climate change and urban development from a social and economic point of view.

The new study has been partially based on previous OECD works, which classified the world's port cities on a scale based on their present and future vulnerability to storms taking into account the number of inhabitants and the value of the goods which could be affected by flooding.

Hallegate et al, have calculated the present and future losses due to flooding in 136 of the biggest coastal cities in the world taking into account the existing flood defenses (the city of Amsterdam is an interesting example with and extremely high exposure but small economic average annual losses due to it's extraordinary defenses).

The average losses in 2005 were quantified to be around 6.000 million dollars and could increase up to the mind-bending number of 52.000 million per year by 2050.

According to this metric, most of the more vulnerable cities in the world  are part of industrialized countries such as: Guangzhou and Shenzhen in China, Miami, Tampa-St. Petersburg, Boston, New York and New Orleans in the US, Bombay in India, Nagoya and Osaka-Kobe in Japan and Vancouver in Canada.

Due to their high wealth and low protection level, three US cities (Miami, New York and New Orleans) explain 31% of total economical losses in the 136 cities. Adding the Chinese city of Guangzhou, the four cities explain 43%.

The economic cost in dollars is a way of assessing the risk but a more complete way of assessing it is to see these economical losses as a percentage of the city's total wealth.

According to this criteria, Guangzhou (China), Guayaquil (Ecuador), Ho Chi Minh (Vietnam) and Abidjan (Ivory Coast) are within the most vulnerable cities in the world.

To estimate future climate change impact, a sea level rise between 0.2m and 0.4m by 2050 is assumed.

In addition to this, about a quarter of these 136 cities are located in river deltas, and therefore more exposed to river floods, as well as decreases of soil on land or promotion of coastal seabed, due to the local subsidence, particularly in cases where overexploitation of groundwater accelerates natural processes.

In my opinion, one of the most important findings of this study is that even a "moderate" sea level rise would cause substantial increases in losses if adaptation measures are not taken because the defenses against flooding are designed to past conditions.

Doing nothing is not an option, as it could cause losses exceeding one trillion or more per year, according to the study. 

Therefore, coastal cities will have to improve its flood action plan, including the construction of good defenses, at an estimated cost of around 50,000 million dollars per year to 136 cities.

The report makes the point that significant increases in the flooding risk in cities which are not vulnerable today may occur.

The five cities with the highest estimated risk increase are Alexandria in Egypt, Barranquilla in Colombia, Naples in Italy, Sapporo in Japan, and Santo Domingo in the Dominican Republic.