Flash flood prediction modeling in the hilly regions of Southeastern Bangladesh: A machine learning attempt on present and future climate scenarios

• Machine learning models were used to predict flash flood risks in southeastern Bangladesh. • Random Forest emerged as the most accurate model for flood susceptibility mapping. • Climate change scenarios SSP126 and SSP585 project an increase in high-risk flood areas. • Flood prediction results inform strategies for effective mitigation and adaptation in Bangladesh. Flash floods are highly destructive, and their frequency and intensity are expected to escalate due to climatic changes. This study investigated flash flood susceptibility (FFS) by applying machine learning algorithms and climate projection to predict both present and future hazard scenarios in the southeastern hilly regions of Bangladesh. This study evaluated twelve flood-influencing factors: elevation (EL), slope (SL), aspect (AS), Drainage density (DD), Distance to stream (DS), Topography roughness index (TRI), Stream power index (SPI), Topographic wetness index (TWI), Soil permeability (SP), Precipitation (PR), Land use and Land cover (LULC) and Normalized difference vegetation index (NDVI). Earth observation data, field surveys, and past flood records were used to create a detailed flood inventory. Among the machine learning models tested, the Random forest (RF) algorithm outperformed others, including Support vector machine (SVC), Logistic regression (LR), and Extreme gradient boosting (XGBoost), and was subsequently used for flood susceptibility mapping based on future precipitation projections under two CMIP6 climate change scenarios: SSP126 and SSP585. Our findings indicated that the areas at high to very high risk of flooding are projected to increase significantly under both the SSP126 and SSP585 scenarios. Initially, around 38% of the studied region had high to very high flood susceptibility, but this is expected to rise to 40-42% over the projected time periods. These spatial delineations of flood-prone areas can provide guidance for developing effective mitigation and adaptation strategies to address the adverse impacts of flash flooding in the hilly river basins of Bangladesh.