Flooding Risk From Climate Change

SEPT. 23, 2014

If global carbon emissions continue on current trends and sea levels are affected by climate change about as much expected, about 3.1 percent of the global population (about 216 million people) will be living in a place at risk of regular flooding.

 

These figures are the result of a new analysis of sea levels and flood risk around the world, conducted by Climate Central and based on more detailed sea-level data than has previously been available. The analysis offers country-by-country estimates for populations at risk of regular flooding, accounting for a range of potential emissions reductions and for variations of sea level sensitivity to climate change.More than a quarter of Vietnam’s residents live in areas likely to be subject to regular floods by the end of the century. Four percent of China’s residents — 50 million people — live in the same kind of areas. Across the globe, about one person in 40 lives in a place likely to be exposed to such flooding by the end of the century, absent significant changes.

Globally, eight of the 10 large countries most at risk are in Asia. The Netherlands would be the most exposed, with more than 40 percent of its country at risk, but it also has the world’s most advanced levee system, which means in practice its risk is much lower.

Some countries in Asia may choose to emulate the Dutch system in coming decades, but some of the Asian nations are not wealthy and would struggle to do so.

The analysis offers more evidence that the countries emitting the most carbon aren’t necessarily the ones that will bear the brunt of climate change. The United States — one of the world’s largest carbon emitters per capita and historically the overall largest emitter — ranks 34th on the list of risk of flood exposure, between India and Madagascar. The share of Americans projected to be exposed to regular flooding — about 1 percent — might seem small, but it’s still about 3.1 million people, more than live in Chicago and Minneapolis combined.

China, on the other hand, leads the world in both current emissions and greatest number of people exposed to flood risk.

Climate Central, a news organization and research group, has released the new analysis as the United Nations gathers this week for a summit on climate change. Climate scientists expect flooding to increase as global warming melts snow and ice and expands the volume of oceans. The analysis defines regular flooding as a flood at least once every three years.

Of course, there is substantial uncertainty about the future of carbon emissions, global warming and sea levels. The map above includes estimates, given current trends, for the most likely possibility but also the extreme low and high estimates for sea levels and flood risk. Climate change could occur at a different pace than expected, and governments will surely vary in the aggressiveness of their policy responses.

■ About 2.6 percent of the world’s population — about 177 million people — live in areas that will be vulnerable to chronic flooding within the next 100 years. At minimum, even with extremely rigorous cuts to global emissions and with oceans much less sensitive to climate change than expected, 1.9 percent of the population of coastal countries would be affected. At worst, the figure would be 3.1 percent.The analysis, conducted by Benjamin Strauss and Scott Kulp, finds:

■ Flood-exposure estimates, including those shown above, may still understate the risks. Using more detailed elevation data for the United States than is available globally, for instance, the group found that estimated flood exposure was probably much too conservative. Applied globally, that means more than 500 million people could be living in places that are at risk of regular flooding in the next century.

Climate Central has published a detailed description of its methodology and data on its website.