Sea-level rise from land subsidence in major coastal cities

Coastal cities face a compound threat from relative sea-level rise and land subsidence; however, local land subsidence rates are spatially variable and can be difficult to quantify. Remote interferometric radar observations allow high-resolution estimations of local land subsidence to better inform the future of major coastal cities. Coastal land can be lost at rapid rates due to relative sea-level rise (RSLR) resulting from local land subsidence. However, the comparative severity of local land subsidence is unknown due to high spatial variabilities and difficulties reconciling observations across localities. Here we provide self-consistent, high spatial resolution relative local land subsidence (RLLS) velocities derived from Interferometric Synthetic Aperture Radar for the 48 largest coastal cities, which represent 20% of the global urban population. We show that cities experiencing the fastest RLLS are concentrated in Asia. RLLS is also more variable across the 48 cities (-16.2 to 1.1 mm per year) than the Intergovernmental Panel on Climate Change estimations of vertical land motion (-5.2 to 4.9 mm per year). With our standardized method, the identification of relative vulnerabilities to RLLS and comparisons of RSLR effects accounting for RLLS are now possible across cities worldwide. These will better inform sustainable urban planning and future adaptation strategies in coastal cities.

Automated summary

Coastal cities are facing a dual threat from rising sea levels and land subsidence, but it is challenging to quantify the variability of local land subsidence rates. Remote interferometric radar observations can provide high-resolution estimations of local land subsidence, improving our understanding of future prospects for major coastal cities. Using this method, we found that the fastest rates of local land subsidence are concentrated in Asia. The variability of local land subsidence across the 48 cities studied is greater than the estimations of vertical land motion by the Intergovernmental Panel on Climate Change. Our standardized method allows for the identification of relative vulnerabilities to local land subsidence and facilitates comparisons of the effects of sea-level rise that account for local land subsidence.