Compound coastal flood exposure in global deltas: an integrated assessment of sea-level rise, subsidence, and socioeconomic dynamics

Delta regions worldwide face escalating coastal flood risks driven by the compound effects of sea-level rise (SLR) and vertical land motion (VLM). Existing studies often analyze these hazards separately and rely heavily on simplified static inundation models, limiting the accuracy of flood impact assessments and neglecting dynamic socioeconomic factors. This study develops an integrated framework combining high-resolution VLM monitoring (SBAS-InSAR), dynamic hydrodynamic modeling (LISFLOOD-FP), and socioeconomic projections (Shared Socioeconomic Pathways: SSP1-2.6, SSP2-4.5, SSP5-8.5) for comprehensive flood impact evaluation in three globally significant deltas: the Ganges-Brahmaputra-Meghna (GBM), Mississippi, and Yangtze. Results highlight severe and spatially variable subsidence rates—most notably in the GBM Delta (–8.98 mm/year), followed by the Mississippi (–2.93 mm/year) and Yangtze (–1.60 mm/year)—with human activities likely playing an important role in driving surface deformation. Projected flood scenarios (2050 and 2080) indicate significant increases in inundation extents and exposed populations and economic assets, particularly under combined SLR + VLM scenarios. The Yangtze Delta shows the highest economic exposure (up to approximately 1 trillion USD), whereas the GBM Delta exhibits the greatest demographic vulnerability, potentially affecting approximately 20 million individuals. The relative contributions analysis emphasizes an increasing dominance of SLR over time, especially under high-emission scenarios. These findings underscore the critical importance of tailored, region-specific adaptation strategies including resilient infrastructure, nature-based solutions, and adaptive spatial planning.