Coastal communities around the world are facing an increasing flood threat as the land beneath many cities continues to sink, causing residents to experience sea level rise at nearly three times the global average, according to a study published in Nature Communications.
Researchers from the Technical University of Munich (TUM) and Tulane University found that people living in densely populated coastal regions are experiencing an average relative sea level rise of about 6 millimetres per year, compared to the global coastal average of 2.1 millimetres annually.
The study attributes the accelerated rise primarily to land subsidence the gradual sinking of the ground caused by excessive groundwater extraction, oil and gas production, sediment compaction in river deltas, rapid urbanisation, and natural geological processes.
Countries including Thailand, Bangladesh, Nigeria, Egypt, China and Indonesia recorded some of the highest rates of relative sea-level rise, ranging from 7 to 10 millimetres per year. The United States the Netherlands and Italy also showed elevated rates of around 4 to 5 millimetres annually.
Among major cities, Jakarta recorded the fastest average land subsidence at 13.7 mm per year, followed by Tianjin (13.5 mm/year), Bangkok (8.5 mm/year), Lagos (6.7 mm/year) and Alexandria (4 mm/year). In some parts of Jakarta, the ground is sinking by as much as 42 mm annually.
The researchers said improved groundwater management, stricter regulation of water extraction and artificial recharge of aquifers could significantly slow or even halt land subsidence. They cited Tokyo and the Harris Galveston region in Texas as examples where policy interventions successfully reduced sinking rates.
The study highlights that tackling land subsidence alongside climate driven sea level rise is essential to reduce flood risks for the more than 500 million people living in low-lying coastal regions worldwide.