Small but inevitable rises in sea level will double the frequency of severe coastal flooding in most of the world with dire consequences for major cities that sit on coastlines, according to scientists.
The research takes in to account the large waves and storm surges that can tip gradually rising sea levels over the edge of coastal defences. Lower latitudes will be first affected, in a great swath through the tropics from Africa to South America and throughout south-east Asia, with Europe’s Atlantic coast and the west coast of the US not far behind.
The most vulnerable places, including large cities in Brazil and Ivory Coast, and small Pacific islands, are expected to experience the doubling within a decade.
“It is pretty much inevitable that we are going to see increased frequency of extreme water levels – there is no way around this,” said Sean Vitousek, at the University of Illinois at Chicago, who led the research.
Climate change is causing sea levels to rise at about 4mm per year, as ice caps melt and the oceans warm and expand. This will continue for many years due to the carbon dioxide emitted into the atmosphere.
The steady rise in sea level is unlikely to cause flooding directly as coastline developments are designed to withstand the larger ebb and flow of the tides. But the rising level gives a higher starting point for the storm surges and big waves that can overwhelm coastal defences.
The research, published in the Scientific Reports journal, is the first to analyse these factors, particularly waves, on a global scale. It found that the most at-risk areas were in the low latitudes, where tidal ranges are smaller meaning sea level rise is proportionally more significant.
In those locations, just 2.5cm of sea level rise leads to extreme water levels being seen twice as often, while a 5-10cm increase means coastal floods are twice as likely across all the tropics. A rise…