Risk of intensified storm surges: High stakes for developing countries

Photo © Syed Zakir Hossain/Greenpeace

We are now faced with overwhelming scientific evidence that more intense storm surges and sea-level rise from climate change are serious global threats. Increased cyclonic activity and heightened storm surges are expected from the rise in sea surface temperature now observed at all latitudes and in all oceans. Even small changes in sea level profoundly affect storm surge height and the extent of flooding in coastal zones and adjoining low-lying areas. I think there is a dire need for greater disaster preparedness in countries vulnerable to such storm surges.

Recently, Benoit Laplante, Siobhan Murray, David Wheeler and I considered the potential impact of a large (one-in-100-year) storm surge by contemporary standards, and then compared it with the intensification which is expected in this century. We used satellite maps of the world overlaid with comparable data for 84 coastal countries to calculate the toll of such changes on affected territory, people, GDP, urban areas, agricultural areas and wetlands in five developing regions.

Our paper takes both a global and regional perspective. Globally, our estimates show that about 19.5% (391,812 km2) of the combined coastal territory of 84 countries is vulnerable to inundation from a one-in-100-year storm surge by current reference standards. A 10% future intensification increases the potential inundation zone to 25.7% (517,255 km2), taking into account sea level rise. This translates to an inundation threat for an additional 52 million people; 29,164 km2 of agricultural area; 14,991 km2 of urban area; 9% of coastal GDP and 29.9% of wetlands.

These impacts are not uniformly distributed across the regions and countries of the developing world. The Latin America & the Caribbean region has the largest percentage increase in storm surge zone area, but the coastal population impacts are largest for the Middle East & North Africa, while coastal GDP losses are most severe in East Asia.

Because GDP per capita is generally above average for coastal populations and cities, we estimate that storm surge intensification would cause additional GDP losses (above the current one-in-100-year reference standard) of $84.9 billion in the East Asia & Pacific region, $12.7 billion in the Middle East & North Africa, $8.4 billion in South Asia, $14.4 billion in Latin America & the Caribbean and $1.8 billion in Sub-Saharan Africa.

We note that some low-income countries are susceptible to very significant damage. For the majority of indicators we studied, El Salvador, Yemen, Djibouti, Mozambique, and Togo are expected to experience the most severe impacts.

We have also identified the top 10 major urban centers worldwide that are located in storm-surge zones. Once again, alarmingly, most of these are in poor countries. This highlights the potentially deadly exposure of their inhabitants, since storm water drainage infrastructure is often outdated and inadequate. The risks may be particularly severe in poor neighborhoods and slums, where infrastructure is often nonexistent or poorly designed and ill-maintained.

There is a very strong case for rapid action to protect endangered coastal populations. Knowing which countries and urban centers will be most affected will allow better targeting of scarce resources and could spur adaptation plans for coastal zone now and avoid big losses later.

If you're interested in research about port cities vulnerable to storm surges, try reading Ranking Port Cities with High Exposure and Vulnerability to Climate Extremes by Nicholls, Hanson, Herweijer, Patmore, Hallegate, Corfee-Morlot, Chateau, and Muir-Wood, OECD Environment Working Papers series (No.1). For more on global warming, tropical cyclones, and storm surges, I’d recommend Hurricanes and Global warming: Results from Downscaling IPCC AR4 Simulations by Emanuel, Sundararajan, and Williams.