Nationwide Multi-Scenario GLOF Hazard Mapping in Nepal Using Remote Sensing and Hydrodynamic Modelling

Rapid glacier retreat in the Nepal Himalaya has accelerated the formation and expansion of glacial lakes, increasing the likelihood of glacial lake outburst floods (GLOFs) with potentially severe downstream consequences. Existing GLOF studies in Nepal are largely site-specific and lack national-scale consistency, limiting their utility for systematic hazard planning. Here, we present a comprehensive, multi-scenario GLOF hazard assessment for Nepal based on three decades of satellite observations (1990–2023) and large-scale hydrodynamic modelling. Using multi-temporal remote sensing, we mapped 1,232 glacial lakes, including 265 newly formed lakes, and estimated lake volumes and peak discharges using established empirical relationships. Downstream flood propagation was simulated using the LISFLOOD-FP hydrodynamic model, enabling consistent, high-resolution inundation mapping across the country. To examine plausible future conditions under continued glacier retreat, we implemented scenario-based lake-volume increases of 10–50%, representing optimistic, intermediate, and pessimistic states. Results indicate a ~26.9% increase in total glacial lake area since 1990, with the most pronounced expansion in the Koshi and Karnali provinces. Modelled inundation extents and flood depths, particularly exceeding 3.5 m, increase substantially under higher-volume scenarios. Koshi and Karnali consistently emerge as the most exposed regions, with heightened impacts on settlements, hydropower infrastructure, and transport networks. The resulting national-scale GLOF hazard atlas provides a coherent framework for visualising present and future flood hazards and offers a practical basis for climate adaptation planning and disaster risk reduction in high-mountain regions.