Can high-resolution convection-permitting climate models improve flood simulation in southern Quebec watersheds?

Abstract. In August 2024, Montreal and its surroundings, located in the south of the Quebec province, experienced one of its most destructive meteorological events in history, associated to the remnants of the tropical storm Debby, according to the Insurance Bureau of Canada (Published on 2024, September 13). With climate change, the frequency and intensity of extreme weather events are expected to increase, explaining why government and private sectors, particularly insurance companies, requires enhancing their preparedness. Recent studies highlighted the potential of high-resolution climate models (with grid sizes smaller than 4 km) to improve precipitation extremes at sub-daily timescales. This study focuses on heavy rainfall events during the warm season, comparing outputs from the latest Canadian Regional Climate Model (CRCM6/GEM5) at 12 km and 2.5 km resolutions. For the first time, we estimated that the CRCM6/GEM5-2.5km better captured the intensity of extreme hourly rainfall events compared to the CRCM6/GEM5-12km, aligning more closely with weather station data. To assess whether this added value extends to hydrological modeling, we used a lumped hydrological model to simulated water flows at an hourly time step for 11 basins located over southern Quebec for the period 2001–2018. For most basins, summer-fall peak flows simulated using the CRCM6/GEM5-2.5km had lower biases compared to those simulated with the CRCM6/GEM5-12km. These findings emphasize the importance of high-resolution climate models in improving extreme event simulations, which is essential for better risk assessment and adaptation strategies in a warming climate.