New research shows that parts of San Francisco are experiencing a fast rate of sinking, which, as sea levels rise, will make flooding worse in the Bay Area, with areas sinking up to 1 centimeter (0.4 inches) in a year.
As reported in Science Advances, the researchers used synthetic aperture radar interferometric measurements and GPS data to work out the changes in coastline elevation in the Bay Area between 2007 and 2011. They found that a few areas were rising, like Santa Clara Valley, due to an increase in water storage underground. But the situation was quite bleak in other locations.
"Although we found that most of the Bay's shoreline is sinking by less than 2 millimeters a year, in several areas we discovered subsidence rates of 10 millimeters a year and more," lead author Manoochehr Shirzaei, from Arizona State University, said in a statement.
Treasure Island and Foster City are such places, and so is San Francisco International Airport. The researchers estimate that nearly half of the airport runways and taxiways will be underwater by the end of the century.
"The ground goes down, sea level comes up, and flood waters go much farther inland than either change would produce by itself," Shirzaei added.
The researchers point out that maps considering flood risk don’t include subsidence measurements. Without taking into account elevation changes, many estimates and models for sea level rise might fall short. And while the research focused on San Francisco, this is likely a worldwide problem.
"Flooding from sea level rise is clearly an issue in many coastal urban areas," stated co-author Roland Bürgmann from the University of California, Berkeley. "This kind of analysis is probably going to be relevant around the world, and could be expanded to a much, much larger scale."
According to different sea level rise scenarios, between 51 and 413 square kilometers (20 to 160 square miles) of the Bay Area will face flooding by the year 2100. But when the sinking is taken into account the area is notably larger – between 125 and 429 square kilometers (48 to 166 square miles).
The researchers hope that the data will help local authorities to make better flood resilience plans.