The contribution of atmospheric rivers to ice-related flooding in Québec, Canada, from 1990 to 2022

In the province of Québec in eastern Canada, ice-related floods (IRF) have affected several municipalities and caused over 50 million dollars in personal damage over the past 35 years. Dynamic river ice breakup occurs when river discharge increases due to snowmelt runoff and rainfall, before any significant thermal deterioration of the ice cover. Fragmented ice blocks then jam at river constrictions, triggering the formation of ice jams and consequently flooding adjacent urban areas. Atmospheric rivers (AR) are long and narrow corridors of high-water vapor transport that travel poleward and often result in large amounts of rainfall. Although the frequency of mid-winter ice breakup and AR have increased in recent years in eastern Canada, the effect of AR on IRF has never been investigated systematically at the regional scale. This study assesses the impact of AR on IRF in Québec from 1990 to 2022. To investigate the influence of streamflow, surface, and atmospheric conditions on IRF, we leveraged a provincial flood-related insurance claim database along with the publicly available repository of historical ice jams (IJ) in Québec, the Québec hydroclimatic Atlas dataset of simulated river discharge, the version 3.1 of the Canadian Surface Reanalysis and the EDARA atmospheric river database. Our results show that more than 81% of the 732 analyzed IJ were related to AR conditions, defined as an integrated water transport (IVT) greater than 250 kg m^–1 s^–1. The IJ-related IVT and rainfall intensity were significantly higher in mid-winter (n = 325) than spring (n = 407). In contrast, greater snowmelt contribution during spring IJ resulted in larger streamflow when compared to mid-winter events. Among the mid-winter IJ, those associated to a flood (n = 26) happened under significantly more intense AR conditions. This research demonstrates the significant role of AR on mid-winter IRF and provides new insights for improving winter flood awareness and early warning systems. Next analyses will focus on the characteristics of AR during IJ and IRF.