Coastal land subsidence exacerbates flood risks for coastal cities worldwide, yet its contributions to relative sea level rise (RSLR) remain poorly characterized. Many studies rely on sparse point measurements, excluding land motion or assuming spatial uniformity. This study applied interferometric synthetic aperture radar (InSAR) to map localized subsidence rates and analyze its impacts on RSLR across the urban coastal regions of New York and New Jersey. InSAR’s continuous spatial coverage provides detailed subsidence mapping, which is unachievable through conventional methods. Over 150 Sentinel-1 images were processed using the SBAS technique to generate high-resolution subsidence maps. Moreover, the study delves into local variations in land subsidence rates and validates findings with data collected from GPS stations positioned in Brooklyn, New York, and Sandy Hook Beach, New Jersey. This comparison reveals a significant difference in subsidence rates between Brooklyn showing a rate of 1.2 mm per year with Sandy Hook Beach, recording a more substantial subsidence rate of 2.7 mm per year. These variations underscore the need for localized investigations when addressing the complex interplay between CLM and RSLR. A noteworthy aspect of the study is the method employed to disentangle the contributions of CLM from sea-level rise trends. By subtracting the global mean sea-level rise rate of 3 mm per year from the local sea-level rise rate of 6 mm per year in Sandy Hook, New Jersey, the effects of land subsidence on relative sea-level changes are quantified. This approach reveals that the coastal subsidence rate accounts for approximately 3 mm per year, aligning closely with the observed local sea-level rise in Sandy Hook Beach, New Jersey. Our findings provide vital insights into the contributions of subsidence to increasing coastal flood hazards.
