Integrated flood risk mapping using analytical hierarchy process and geospatial techniques in Lalmonirhat district, northern Bangladesh

The Teesta-Dharla floodplain of northern Bangladesh experiences recurrent monsoon flooding due to transboundary river flows, low elevation, and intense rainfall, necessitating localized flood risk assessment for effective flood management. This study aims to develop an integrated flood risk assessment for Lalmonirhat District using the analytical hierarchy process (AHP) in conjunction with geospatial techniques to quantify flood hazard, vulnerability, and overall risk. Flood hazard was assessed using physical and environmental factors, including elevation, slope, curvature, aspect, topographic wetness index (TWI), rainfall, drainage density, land use/ land cover, normalized difference vegetation index (NDVI), and distance to stream. Vulnerability was characterized using demographic, socio-economic, and service accessibility indicators such as population density, female density, number of children aged 5 to 15, literacy rate, employment rate, settlement density, distance to healthcare, roads, and educational facilities. The integrated flood risk assessment indicates that approximately 34.3% of the Lalmonirhat District falls under high to very high flood risk, while moderate risk dominates around 53.54% of the region, and low to very low risk accounts for 12.16%. Lalmonirhat Sadar and Aditmari emerge as the most risk-prone upazilas, whereas Hatibandha experiences the lowest flood risk despite considerable hazard exposure. The findings underscore the need for targeted intervention by the competent authorities in high-risk upazilas (sub-districts), with emphasis on risk-informed planning, resilient infrastructure development, and community-based preparedness to reduce flood impacts.