Projected Changes to Extreme Freezing Rain Events over Northeastern North America

Freezing rain is an important winter weather hazard, resulting in severe damage to vegetation and infrastructure and making road and air travel dangerous. For example, a recent April 2023 ice storm caused substantial tree damage over regions of Eastern Canada, with over 1.3 million customers losing power in the province of Quebec. Given the impacts of these events, various stakeholders require information on how freezing rain may change in the future as the Earth continues to warm due to anthropogenic greenhouse gas emissions. While several studies have examined how the freezing rain climatology may change, identifying how these high-impact cases may change is more challenging due to their rarity. In this presentation, we examine how extreme freezing rain events may evolve in the future over the northeastern United States and southeastern Canada. To overcome challenges related to small sample sizes, we identify these events in a 50-member high-resolution (0.11°, approximately 12 km) ensemble of simulations using the fifth-generation Canadian Regional Climate Model (CRCM5). These simulations, produced as part of the ClimEx project, were generated by dynamically downscaling 50 members of the CanESM2 large ensemble using observed greenhouse gas and aerosol emissions and land use from 1950 to 2005 and the RCP 8.5 scenario from 2006 to 2099. We identify events exceeding certain thresholds (e.g., 1, 6.35, 10, 20 mm) of freezing rain accumulation. Additionally, we perform an extreme value analysis to identify how the intensity and return period of the most extreme events may evolve in the future. In general, we find an increase in freezing rain frequency and intensity over portions of northern Quebec and Labrador and a decrease elsewhere in southeastern Canada and most of the northeastern United States. However, the most extreme freezing rain events may continue to occur, which may have implications for future infrastructure requirements.