Coastal cities are under threat from rising global sea levels. Now, new satellite images show that coastal megacities are simultaneously sinking, too.
A new satellite launched by the European Space Agency shows how fast areas of land – and the cities built on top of them – are sinking or rising, as the case may be. The results show that cities constructed on deltas are at particular risk of sinking because they lie on layers of soft soil that which are subject to compression, according to an article on Sustainable Cities Collective. When such cities also extract material from beneath the ground, such as oil or groundwater, they face an even greater risk of sinking.
The article explains that New Orleans and Guangzhou in southwest China are both sinking because they are built on deltas. Tokyo, on the other hand, which has sunk more than four metres in the last century, was only able to stabilise this development when it implemented strict measures in the 1970s to stop over extraction of groundwater.
Bangkok suffers from both problems. But while the rate of sinking in the 1950s was up to 10 cm per year, drastic remedial work over the past years has dropped that rate to one or two cm per year.
Jakarta is now the fastest sinking city in the world, lowering at a rate of 5 to 10 cm per year, due to ongoing groundwater extracting and constructing large residential and industrial developments on agricultural land, reports the article. The consequences can be deadly: damage to buildings and infrastructure, flooding in highly populated areas, and destroyed groundwater supplies.