Many of the world’s most densely populated coastal cities are vulnerable to sea level rise because much of their land is sinking rapidly.
A team of international scientists, led by Nanyang Technological University (NTU Singapore), suggests that an increase in industrial processes such as the extraction of groundwater, oil and gas, as well as the rapid construction of buildings and other urban infrastructure, may be contributing to this vulnerability.
For six years, from 2014 to 2020, the team of researchers has captured satellite images of 48 cities and has used a cloud-based processing system called Interferometric Synthetic Aperture Radar (InSAR).
As the sea water is heated and the Earth’s ice caps melt, Sea levels are rising globally. The sea level rises an average of 3.7 millimeters per year globally. Now this problem can be aggravated by subsidence of the earth, according to NTU scientists.
Although ground subsidence varies between neighborhoods and even between blocks, the truth is that in the 48 cities examined, the team found a average sinking rate of 16.2 millimeters per year. They came to verify cases that have land that is sinking at 43 mm per year.
Study Results have been published in the scientific journal Nature Sustainability.
Where are the cities sinking the fastest?
The 48 cities were selected based on the criteria of a Minimum population of five million in 2020, and a maximum distance of 50 kilometers from the coast.
A comparison conducted by the researchers in coastal cities around the world showed that the fastest rates of relative subsidence of local land are concentrated in Asia, especially in Southeast Asia.
The researchers chose to use InSAR because it provides precise measurements of the sinking coast to a tenth of a millimeter.
InSAR maps ground deformation using radar images of the Earth’s surface that are collected from orbiting satellites.
The data sets obtained are larger and more precise, since, unlike visible or infrared light, the radar waves used by INSAR penetrate most of the meteorological clouds and they are equally effective in the dark.
“Our study highlights the fact that while this is a global problem, the response in many cases must be local. Reduce the rate of groundwater extraction to a sustainable level it should be a priority for all municipalities in coastal areas,” said Eric Lindsey, co-author of the study and adjunct professor in the Department of Earth and Planetary Sciences at the University of New Mexico, United States.
The researchers hope to expand the investigation by projecting rates of land subsidence, taking into account variations under various climate and weather scenarios.