The role of narrow fringing reefs in tsunami mitigation: a numerical modelling study along the Sanya coastline

This study assesses the tsunami mitigation capacity of narrow fringing reefs (50–200 m width) under varying ecological health states using a high-resolution implementation of the COMCOT model. Satellite-derived reef bathymetry (20 m resolution) and non-uniform bottom friction coefficients were incorporated to simulate tsunami propagation from four ∼Mw 9 earthquake scenarios along the Manila Subduction zone. The results indicate that healthy reefs can reduce the maximum on-platform current velocities by nearly 80% and delay wave arrival by 5–10 min – providing a critical window for early evacuation. While these narrow coral reefs exert limited influence on initial tsunami wave crests, they significantly attenuate subsequent waves, with up to 50% reduction in wave heights when the peak arrives after the first crest. These findings highlight the disproportionate protective value of healthy narrow fringing reefs, framing them as essential natural infrastructure for tsunami risk reduction. This study offers quantitative thresholds for targeted reef conservation and supports the integration of ecological parameters into computational tsunami hazard modelling frameworks.