Riverine flood risk mapping using GIS–AHP and climate-driven hydrodynamic simulations in an alpine basin of the Indus River system

Abstract

The Swat River Basin (SRB), a mountainous sub-catchment of the Indus Basin, has faced frequent floods in the past 25 years. Limited structural and non-structural measures, such as flood risk mapping, early warning systems, and land use planning, continue to expose the SRB. This study assessed and mapped riverine flood risk using the GIS-based Analytical Hierarchy Process (AHP) and simulated flood extent under current and future climate scenarios using hydrodynamic modelling. The GIS–AHP framework found that the most important factors for hazards and vulnerabilities were precipitation, elevation, and population density. The resulting flood risk map indicated that approximately 29% of the SRB falls within high-to-very-high risk zones, mainly concentrated in populated floodplains and agricultural lands. HEC-RAS 2D simulations projected that under a high-emission climate scenario of 21 st -Century, flood depths could reach up to ~31 m with velocities exceeding ~6 m/s, inundating ~26% of the Area of Interest (AOI), i.e., the high to very high risk zone in the Chakdara downstream part of SRB. The integrated methodology is novel in combining hazard, vulnerability, and hydrodynamic simulations and is transferable to other mountainous, snow- and glacier-fed basins, providing a robust tool for flood risk assessment and mitigation. These results show the significance of integrated strategies, climate-resilient planning, and better land use management to lower the flood risk and protect vulnerable communities.