Spatial Modelling of Ice-Jam Susceptibility in Southern Quebec: An Enhanced Ice Jam Predisposition Index

Abstract. Ice jams represent a recurrent natural hazard in Quebec, where geomorphological and structural river characteristics play a key role in determining their spatial distribution. This study improves and evaluates the Ice Jam Predisposition Index (IJPI) using a dataset of 35 rivers across southern Quebec. The enhanced model integrates geomorphological parameters, including channel narrowing, sinuosity, and slope, along with structural (bridge) and hydrological (tributary) features to delineate reaches prone to ice-jam formation. Including rapids as an inverse indicator helps distinguish high-energy segments where jams are unlikely to occur. Model validation shows that over 90 % of observed ice jams occurred in reaches with medium to high predisposition, with an overall recall of 0.90, indicating promising performance as a screening tool. The results highlight the dominant influence of flat slopes, channel confinement, and curvature on jam formation, suggesting that the model can serve as a useful spatial tool for regional ice-jam risk management. These results demonstrate the potential of the proposed framework to support operational flood risk management by allowing proactive identification of vulnerable river sections. Decision-makers and emergency management agencies can use the model to prioritise monitoring efforts and improve preparation for ice-jam-related hazards.