Sea Level Rise Vulnerability Mapping for Low-Lying Coastal Megacities
DOI:
https://doi.org/10.5281/zenodo.22801061Keywords:
sea level rise, coastal megacities, land subsidence, storm surge, flood exposure, InSAR, digital elevation model, population exposure, critical infrastructure, climate adaptationAbstract
Low-lying coastal megacities face a compound flood hazard in which global mean sea level rise interacts with local
land subsidence and storm surge to produce relative water-level increases far larger, and far more spatially uneven,
than sea level rise alone would suggest. We built a composite exposure and vulnerability map for five coastal
megacities, Jakarta, Lagos, Dhaka, Ho Chi Minh City and Miami, combining a coastal digital elevation model
corrected against ICESat-2 and airborne lidar validation points, a decadal Sentinel-1 InSAR subsidence record
(2015-2022), sixth Coupled Model Intercomparison Project (CMIP6) sea level rise projections under SSP2-4.5 and
SSP5-8.5 for 2050 and 2100, and a 1-in-100-year storm surge return-level estimate for each city, to generate
bathtub-model flood extents refined by hydrological connectivity, which we intersected with gridded population
(WorldPop) and OpenStreetMap-derived critical infrastructure layers. Composite relative sea level rise by 2100
under SSP5-8.5, sea level rise plus subsidence, ranged from 0.53 m in Miami, where subsidence is localized and
slow, to 2.61 m in Jakarta, where subsidence locally exceeds 10 cm per year in groundwater-depleted districts, an
order of magnitude greater than the eustatic contribution alone. Across the five cities, the population exposed to the
combined 1-in-100-year storm surge on this composite surface reached an estimated 20.8 million residents by 2100
under SSP5-8.5, more than triple the 6.4 million exposed under present-day mean sea level, with Dhaka and
Jakarta together accounting for 61% of the added exposure. Critical infrastructure counts followed a similar pattern,
with the number of exposed health facilities across all five cities rising from 187 at present to 612 under the 2100
high-emissions composite scenario. Subsidence, rather than eustatic sea level rise, was the dominant driver of
projected exposure growth in three of the five cities. These results indicate that vulnerability assessments relying on
eustatic sea level rise projections alone substantially underestimate near-term flood exposure in
subsidence-affected megacities, and that groundwater management is, in such settings, as consequential for
coastal flood risk as global emissions trajectories.
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