Spring flooding in Southern Quebec: a hydrometeorological assessment of the 2017 and 2019 events

During the 2017 and 2019 spring freshets, exceptional peak flows affected a number of regions of southern Quebec, resulting in property damage of hundreds of millions of dollars. The analysis in this article aims to document the large-scale hydrometeorological conditions associated with these floods over the southern part of the province. The main results show that record-breaking flows were reported during the spring freshets in 17% of the studied catchments during these two years. Eight percent of the catchments reported flows higher than ever before in 2017, and three of these catchments broke their records again in 2019. These floods were primarily caused by intense rainfall events which surpassed the 95th percentile by more than 150%. These rainfall events accelerated snowmelt, with quantities more than 200% of the 95th percentile, contributing exceptional, and sometimes extreme, inputs of water throughout the province. Higher peak flows occurred in catchments with smaller surface areas and high flashiness. On the other hand, regulated catchments had relatively low peak flows.