The impacts and future changes of near-freezing precipitation events in Québec

Near-freezing precipitation (NFP) events, a type of multivariate event compounding temperature and precipitation, are associated with widespread power outages. In a society undergoing an energy transition towards electrification, outages are associated with large impacts. Thus, understanding the impacts and the future evolution of NFP events in a changing climate is increasingly important. In this study, we first establish the relation between outages and NFP events, based on reanalysis data and on a Québec-based utility outage dataset. The highest density of outages in the region is found to occur in association with mixed precipitation near the freezing point. Next, daily NFP totals in various reanalyses are evaluated against Environment Canada weather stations in power-line-dense regions of Québec, to select a gridded reference. The Canadian Surface Reanalysis (CaSR) performs best and is selected. Then, a 28 member CMIP6 ensemble, bias-adjusted using CaSR, is used to evaluate future regional changes in the frequency of near-freezing precipitation events, as a function of time and as a function of local warming. In general, it is found that warmer areas south of Québec see a decline in the frequency of events, while colder northern areas see an increase. The number of days with near-freezing precipitations over 5 mm liquid equivalent varies non monotonically with annual temperature. This number will decrease by up to 40% south of Québec in the future and increase in the north. At the latitude of Montréal, the number of days may first increase and peak before decreasing again at the end of the century, as more wet snow turns to rain. However, rare events show a more uniform pattern of increasing intensity than NFP indicator, with slight decreases mostly near the coasts in the south. For Montréal, end of century NFP increases are more preeminent in ssp245, than in the warmer scenarios, which are likely further past the maximum risk. These findings on the impact of NFP events on the grid, as well as on the future evolution of these events, can directly inform the costly grid-hardening strategies considered for future adaptation.