Flash floods in traditionally less flood prone areas of southeastern Bangladesh

Abstract

The growing threat of climate-driven urban flash floods signifies the need for rapid damage assessment tools. Understanding the impacts of sudden floods on populations and croplands in historically less flood-prone regions is essential for effective risk management. This study highlights the significant impact of the flood event that began on August 20, 2024, affecting three southeastern districts of Bangladesh Noakhali, Feni, and Cumilla that had experienced minimal flooding in the past three decades. Using Google Earth Engine and Synthetic Aperture Radar images, we mapped the extent of the flooding and assessed the damage to croplands and settlements, with findings validated by planet optical images, water level data, published reports and newspapers. Cumulatively, the three districts recorded a total inundation of 2564.78 km² (31.21% of total area), affecting 53.05% (1686.32 km²) of the total cropland, 52.75% (188.15 km²) of the settlements, and 10.2% (1102976 individuals) of the population. While Cumilla bore the brunt of the disaster, the impact across all districts underscores the complex interplay of geography, land use, and infrastructure in determining flood vulnerability. The primary causes of the flood appear to be extreme rainfall in Tripura combined with already saturated surfaces from monsoon rains, with heavy discharge from the Dumbur Dam considered a plausible but hydrologically unverified contributing factor. This situation was further exacerbated by river siltation, unplanned urbanization, and inadequate infrastructure, leading to extensive damage. The findings emphasize proactive early warning, nature-based solutions, and multi-stakeholder strategies for disaster preparedness, risk reduction, and effective relief distribution.