Read More: New Scientist
Rising seas aren’t the only problem facing low-lying coastal areas. Many of these areas are also sinking, vastly increasing the risk of flooding. In the San Francisco Bay area, sea level rise alone could inundate an area of between 50 and 410 square kilometres by 2100, depending both on how much action is taken to limit further global warming and how fast the polar ice sheets melt. But when land subsidence is also taken into account, the area vulnerable to flooding during high tides and storm surges rises to between 130 and 430 square kilometres. That’s the conclusion of Manoochehr Shirzaei at Arizona State University and Roland Bürgmann at the University of California, Berkeley. They used satellite data from 2007 to 2010 to work out how land heights changed in the Bay area at this time. A few areas such as Santa Clara Valley were rising slightly, likely because of increased groundwater storage. But most areas were sinking slightly, by 1 or 2 millimetres per year. Slowly sinking Some places, including parts of the city itself, plus San Francisco International Airport and Foster City, were sinking by up to 10mm per year. That’s because these areas are built on natural mud deposits, or landfill sites that are still compacting.