Sensitivity of Flood Extent and Population Exposure to Variations in Bathymetry Across a Shallow Continental Shelf Lagoon

Abstract Bathymetry is a critical input to storm surge models on coastlines fronted by lagoon systems, yet few studies explore how variations in bathymetry influence flood impacts, flooded extent, and exposed population across these globally widespread morphologies. Here, we investigate the influence of variations in bathymetry on storm inundation impact estimates across a continental shelf lagoon system. We explore how flooded extents and exposed population estimates from a 1% storm for Belize vary with estimated depths by comparing three existing bathymetries over a northern shallow, enclosed lagoon and a central deeper, open lagoon system with a newly developed bathymetry data set, Satellite‐Derived Bathymetry Enhanced Data set‐SDBED. We compare multiple bathymetric data sets to understand the influence on the flood uncertainties and the quantity of the impact of exposed population estimates. Our results show that greater estimated lagoon depths consistently result in lower predicted flood impacts for both lagoon systems in almost all cases. Unexpectedly, for one bathymetry with a median depth of 2 m in the northern lagoon, we find that a reduction in lagoon volume by 59% reduces total inundation volume by 45%. Our findings also show how vertical uncertainties in the SDBED bathymetry propagate through the model, resulting in variations of up to 12% in flood extents and up to 2% in exposed populations.