Inundation crisis in North China coastal gateway amid sinking lowlands, rising sea levels, and engineering initiatives

Sea level rise causes land loss and threatens coastal communities. Although sea level projection has incorporated vertical land motion is often overlooked in quantifying the pathway and extent of seawater overflow, and the attendant land loss and exposed population in future coastal inundation. Here we use the satellite Interferometric Synthetic Aperture Radar to obtain the relative local land subsidence along the coastal gateway of North China - Bohai Economic Rim - a major seaway near Beijing. Our results show that a combination of natural lowlands and human-induced subsidence can lead to alarming inundation risks. The Intergovernmental Panel on Climate Change framed relative sea level rise alone can cause a land loss of 392–497 km², while relative local land subsidence can further amplify the land loss by 110%-260%. Existing initiatives including levee construction and land elevation can alleviate the risks: by 2100, such initiatives can reduce flood extents by ~ 400 km² and exposed populations by ~ 111,000, yet continuous efforts are warranted. In an aging society, adults in the Bohai Economic Rim face 10% greater exposure to inundation due to industry concentration. Our study demonstrates the importance to synergize relative local land subsidence for high-fidelity coastal inundation assessment.