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Sans Protective Measures, Flooding Damage Could Cost the World $1 Trillion by 2050

Coastal cities—rich and poor—share the risk, and face tough decisions about how to adapt to rising seas and stronger storms
flooded city dock in annapolis, Maryland



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New flood research makes one thing clear about the deleterious effects of global warming: they are not problems developing nations will have to face alone.

As Earth warms and sea levels rise, governments in vulnerable areas will have a tough choice to make. Whereas more affluent nations will likely spend millions on structural flood barriers to protect existing coastal real estate, poorer regions with more transient populations may need to encourage settlement in safer inland areas. In places that do choose to fork over the cash for protection systems the frequency of floods will decrease, but those that are big and strong enough to breach the barriers will be more devastating.

World Bank economist Stephane Hallegatte, along with a team of scientists and engineers, studied 136 cities across the world to see how each would fare as sea levels rise between 2005 and 2050. Their study, commissioned by the Organization for Economic Cooperation and Development (OECD) was published in the August 18 edition of Nature Climate Change. (Scientific American is part of Nature Publishing Group.) The damage from floods in that period will be clustered in just four cities: three in the U.S., Miami, New York and New Orleans; and one in China, Guangzhou, Hallegatte found.

To avoid facing up to $1 trillion in annual flood-related damages for the period 2005-2050, the governments of the most at-risk regions would need to spend a collective $50 billion on structural adaptations, complex systems of adjustable dykes, gates and levies that they would be able to raise and lower according to the location and nature of the risk.

Dale Jamieson, who directs the New York University Environmental Studies program and was not affiliated with the study, says Hallegatte’s findings should be a wake-up call for wealthier nations with at-risk coastal areas who have not taken precautions to prepare for the results of climate change. “What we are beginning to see is that there are large areas of the developed world that are vulnerable as well. The idea that this is a developing world problem is being chipped away at,” Jamieson says.

In cities like Miami, which floods from the inside out because it is built on porous rock, flood prevention systems will have to include a variety of adaptations, from adjustable barriers to complex drainage systems. Amsterdam, which faces flooding threats from the multiple rivers that surround it but also from the lakes to the east, already has one such system installed. Unfortunately, poorer cities that face similar geographic challenges, such as Ho Chi Min City in Vietnam or Abidjan in Ivory Coast, would be unable to afford a similar model, Hallegatte says.

Hallegatte estimates that the necessary adaptations would cost each at-risk city an initial $3 billion, plus 2 percent of the initial cost each year for maintenance and operation, putting the total yearly cost for the 136-city sample in the study at about $50 billion—a quarter of NASA’s space shuttle program.

Even without the money to build these expensive systems, developing nations may still have another option: encourage growing populations to settle in safer areas. This is especially critical because as global flooding worsens and sea levels continue to rise, regions without protection systems will bear the brunt of flooding damage. Of the 20 cities with the highest estimated loss in 2050, a majority are in developing countries, including Egypt, Colombia, the Dominican Republic, Libya and Indonesia. “If you take a country like Africa where cities are growing, we have a real window of opportunity. They are deciding now where to allow new development to take place, and thus where the population will live in the near future,” Hallegatte says.

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