Flash flood potential risk zonation mapping using GIS-based spatial multi-index model: a case study of Sunamganj District, Bangladesh

Intense rainfall in the Meghalaya and Assam regions leads to flash floods in the northeastern Haor region of Bangladesh, as a substantial volume of water enters the Surma River via the downstream river network, resulting in extensive damage. Our objective was to construct a comprehensive geospatial multi-index model, incorporating four key indices (hazard, exposure, sensitivity, and resilience) to assess flood risk in the Sunamganj district. This model considers a range of flood risk indicators related to the district’s economic, social, and physical environment. Risk calculations were carried out using modeling techniques, and principal component analysis (PCA) was applied for composite analysis. The results reveal that approximately 40% of the district’s area (~ 1452.51 km2) falls within high- and very high–risk zones, while around 45% (~ 1554.66 km2) is categorized as very low- and very low–risk zones within the Sunamganj District. Regarding the risk rankings, Dharampasha Upazila stands out with the highest percentage, at around 60%, surpassing neighboring Upazilas like Shalla, Derai, Jamalganj, Dakshin Sunamganj, and Tahirpur. This information offers valuable insights for prioritizing the region’s risk reduction and management efforts. We also note that the Upazilas in the northwestern region of Sunamganj district are situated in a particularly high-risk zone for flash flooding. This heightened risk is primarily due to their low elevation, a notable concentration of deep depressions, and a high drainage density. The recurring flash floods in these areas have significant repercussions, impacting the literacy rate and the socioeconomic conditions of these Upazilas. The current study, employing geospatial and statistical techniques, facilitates the identification of the root causes of flash floods. The findings from this research are expected to provide valuable insights for policymakers and developers, enabling them to formulate strategies to reduce flash flood risks in the region.