Integrating Remote Sensing and Participatory Assessment Techniques to Map Multi-Hazard Vulnerability and Resource Gaps: A Geospatial Study of Socioeconomic Inequity of Coastal Bangladesh

Coastal communities in Bangladesh are increasingly exposed to a range of natural hazards due to their low elevation, the dynamic nature of river systems, and environmental changes driven by climate. This study presents an integrated geospatial framework for assessing multi-hazard vulnerability and mapping community resources in Dakhin Bedkashi Union, Koyra Upazila, a coastal administrative unit bordering the Sundarbans mangrove forest. The research addresses six key hazards that impact the region: riverbank erosion, cyclones, flooding and tidal surges, waterlogging and salinity intrusion, drought, and earthquakes. This study employed a mixed-methods approach combining remote sensing analysis, GIS-based spatial modeling, and participatory assessment techniques. Temporal analysis of riverbank erosion was conducted using Normalized Difference Water Index (NDWI) derived from Landsat imagery (1990–2022) processed in Google Earth Engine. Cyclone exposure was evaluated through historical track digitization (1990–2022) and network analysis to determine shelter accessibility within 500m, 1000m, and 1500m service areas. Flood susceptibility, earthquake risk zonation, and seasonal drought patterns were mapped using datasets from the Bangladesh Agricultural Research Council and Space Research (BRAC) and Space Research and Remote Sensing Organization (SPARRSO). Primary data collection included three Focus Group Discussions (n=47 participants), two Key Informant Interviews, and GPS-based ground truthing of critical infrastructure. Results indicate that river erosion and tidal flooding pose the highest risks to the study area, followed by cyclone exposure and waterlogging. The NDWI time-series reveals progressive land loss along the Kopotakkho River, exacerbated by inadequate embankment construction and proliferation of informal sluice gates for shrimp aquaculture. Network analysis demonstrates that residents in peripheral wards must travel over 45 minutes on foot to reach cyclone shelters, with accessibility further constrained by predominantly unpaved road networks. The area falls within earthquake Zone III (moderate risk) but remains vulnerable to potential tsunami-induced coastal inundation. Community consultations revealed that while cyclone impacts have decreased due to improved early warning systems, chronic hazards including erosion, salinity intrusion, and waterlogging increasingly threaten livelihoods and freshwater security. The resource mapping component identified critical gaps in disaster response infrastructure: only four cyclone shelters and one health facility serve a population exceeding 16,000. Housing vulnerability is acute, with 98% of structures classified as non-permanent (kaccha) construction. This research demonstrates how combining top-down remote sensing with bottom-up community knowledge can expose the hidden spatial dimensions of socioeconomic vulnerability in climate-threatened deltas.