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Southeast Asia's coastal cities sinking fastest

An increase in extraction of groundwater, oil, and gas, as well as the rapid construction of buildings and other urban infrastructure is making many coastal cities vulnerable to rising sea levels as large measures of their land is sinking.

A team of international scientists has found that many densely populated coastal cities worldwide are becoming vulnerable to sea level rise. A comparison carried out by the researchers showed that the fastest velocities of relative local land subsidence are concentrated in Asia, especially in Southeast Asia.

The team of researchers from NTU Singapore, University of New Mexico, ETH Zürich, and NASA’s Jet Propulsion Lab managed by the California Institute of Technology, processed satellite images of 48 cities from 2014 to 2020 using a cloud-based processing system called Interferometric Synthetic Aperture Radar.

A media release by NTU Singapore says that sea levels are rising globally as Earth’s ice sheets melt and as warming sea water expands. According to scientists sinking land can aggravate the problem.

Land subsidence varies at a neighbourhood and even block level but across the 48 cities surveyed, the team found a median sinking speed of 16.2mm per year, while some of them have land that is sinking at 43mm a year. The current global mean sea-level rise is 3.7mm/year.

The results of the study have been published in the September 2022 issue of scientific journal Nature Sustainability.

NTU ASE and the Earth Observatory of Singapore PhD researcher and first author of the paper Cheryl Tay said, “By estimating how much and how fast these densely populated coastal cities are subsiding, our study helps constrain projections of coastal flooding in the coming decades, as we expect more land to be flooded due to rising sea levels and land subsidence.”

The researchers had selected 48 cities based on the criteria of a minimum population of five million in 2020 and a maximum distance of 50kms from the coast.

Asian School of the Environment at NTU acting chair and co-author of the study professor of Earth sciences Emma Hill said, “In coastal areas, sinking land leads to higher sea level and an increased flood risk. Our findings enable affected communities and policymakers to identify which areas are at particular risk from high levels of land subsidence and take action to address their coastal risks.”

The researchers hope to further their study by projecting the rates of sinking land, factoring in variabilities and sensitivities from different climate and weather scenarios.



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