Sea-level rise could put as many as 13.1 million people along the coast of the United States at risk of flooding in the future, reports a new paper published online this week in Nature Climate Change. The study, which accounts for the rapid population growth in coastal areas, suggests that the risk is three times larger than indicated by current populations. Large numbers of people may need to relocate if protective measures are not taken, with projected movements of a magnitude similar to the twentieth-century Great Migration of southern African-Americans.
Sea-level rise is one of the most obvious threats to society as a result of climate change. However, the degree to which sea levels will rise is uncertain, and predicting flood patterns can be difficult due to local geographical variations and uncertainties around future population changes. Previous studies have therefore struggled to quantify the number of people at risk from future sea-level rise.
Mathew Hauer and colleagues address this problem by combining location-specific environmental data, which account for different elevations and flood risks, and small-scale population projections for US coastal states with sea-level rise projections from the National Oceanic and Atmospheric Administration (NOAA). They find that a sea-level rise scenario of 0.9 metres by 2100 will put 4.2 million people in US coastal regions at risk of flooding. If sea levels rise by 1.8 metres, which represents the upper end of NOAA’s projections, that figure will rise to 13.1 million. Florida accounts for nearly half of the total at-risk population, with the southeastern US accounting for nearly 70%.