As if the rising seas weren’t enough, some major cities around the world also have to deal with another problem: They’re sinking.
Well, really, they’re subsiding. A combination of groundwater extraction, the load of heavy buildings on the underlying soil and natural subsidence means that some cities are facing rising sea levels while the ground under their feet is sinking.
Groundwater extraction is one of the most serious causes of subsidence. Tokyo, for instance, sank nearly 6 feet over the course of several decades because it was drawing groundwater from under the city, as the BBC reports:
"Land subsidence and sea level rise are both happening, and they are both contributing to the same problem - larger and longer floods, and bigger inundation depth of floods," Dr Erkens told BBC News.
"The most rigorous solution and the best one is to stop pumping groundwater for drinking water, but then of course you need a new source of drinking water for these cities. But Tokyo did that and subsidence more or less stopped, and in Venice, too, they have done that."
Researchers looked at several coastal cities (Jakarta, Ho Chi Minh City, Dhaka, New Orleans and Bangkok) in danger of flooding and found that cities need to answer some pretty basic questions about subsidence, like "What are the main causes? and "Where are the vulnerable areas?" Answering those questions will be a large part of coastal cities’ futures.