Quantifying impacts of vertical land motion and sea level rise on flooding in Lagos Nigeria

The authors integrate high-resolution VLM into sea-level rise (SLR) projections for Lagos, Nigeria to quantify impacts of vertical land motion and sea level rise on flooding. Using GNSS-referenced Sentinel-1 DInSAR (2015–2025), cross-validated against independent PS-InSAR measurements, we find vertical rates from –11.40 to +0.76 mm/yr (P10-P90), the fastest twice the global mean SLR. Combining these rates with tides and IPCC AR6 SSP2-4.5 projections, in a 2 m connectivity-filtered inundation model, the authors assess three densely populated regions.

In the southwest, projected 2100 flood extent increases 70% from 0.98 to 1.68 km². In the central and southeast mainland, where SLR alone produces minimal flooding (0.15–0.16 km²), subsidence expands projected inundation to 1.71–2.28 km². VLM advances flooding timelines by 48-60 years. Propagating elevation, velocity, and sea-level uncertainties, the authors find sea level projections have the greatest spread, while InSAR uncertainty contributes ≤1.3% by 2100. These estimates are conservative: the surface model masks flooding beneath buildings. This framework is applicable to other subsiding coastal megacities.