Geospatial assessment of natural hazard risks in coastal Bangladesh with a focus on communities outside embankments in Barguna

Bangladesh is highly disaster-prone, with coastal areas exposed to sea-level rise, cyclones, storm surges, flooding, and salinity intrusion, particularly in communities outside embankments. This study developed a Coastal Vulnerability Index (CVI) for outside-embankment areas of Barguna Sadar Upazila by integrating natural hazard intensity, physical-geological conditions, and socio-economic vulnerability. The Natural Hazard Vulnerability Index (NVI), derived from cyclone wind, storm surge, flood depth, salinity, and rainfall using Log-Pearson Type III distributions, increased from 0.35 at the 2-year return period to 0.75 at 100 years. Physical and geological vulnerability (PVI = 0.51) reflected low elevation (mean = 1.09 m), gentle slope (0.25°), dynamic geomorphology, shoreline change (− 4.8 to + 18 m yr⁻¹), and relative sea-level rise (+ 15.08 mm yr⁻¹). Socio-economic vulnerability was comparatively low (SEVI = 0.43), with lower social (0.31) and economic (0.32) vulnerability but higher housing and infrastructure vulnerability (HVI = 0.65). The mean CVI was 0.47, with 3.63%, 28.88%, 49.22%, 15.81%, and 2.47% of the study area classified as very low, low, moderate, high, and very high vulnerability, respectively. NVI and PVI strongly influenced the spatial pattern of the CVI, while comparatively lower SEVI reflected greater household coping capacity, although housing and infrastructure remained important constraints. The return-period-based CVI framework provides a practical approach for assessing directly exposed outside-embankment communities and supporting location-specific coastal adaptation planning.