Quebec grapples with back-to-back thunderstorms, floods this week 

Quebec was hit hard by rounds of severe thunderstorms throughout Thursday. In just a few hours, more than 75 millimetres of rain fell on Quebec City, flooding basements, roads, and highways. 

The storm has been declared a catastrophe (more than $30 million in insured losses), says Glenn McGillivray, managing director of the Institute for Catastrophic Loss Reduction. But he doesn’t expect that event to have as big an impact as last year’s record-breaking flood.  

Nearly a year ago, flooding on Aug. 9 and 10, 2024, caused an estimated $2.7 billion in insured damage — the costliest severe weather event in Quebec’s history.

On Thursday, flash flooding on roads forced about 15 people from their homes, with some residences being evacuated by emergency services, the Canadian Press reports. Torrential rain also led officials to close streets in Quebec City’s historic district. In other parts of Quebec, strong winds damaged trees and triggered power outages. 

It comes just days after widespread, severe thunderstorms drenched southern Quebec on Sunday, knocking down power lines and prompting outages for an estimated 100,000 Hydro-Quebec customers. Parts of Montreal saw between 70 and 80 mm of rain in three hours, surpassing the average rainfall for the entire month of July. The storm caused localized flooding across major intersections and buildings in the southern regions of Quebec.  

It will take some time for loss estimates to be totalled for either of this week’s flood events, says McGillivray.  

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Infrastructure needs overall

McGillivray tells Canadian Underwriter that after last year’s record-breaking flood, and despite two more major flood events in Quebec this week, many areas of the province remain just as vulnerable to flood losses. That’s because the kind of infrastructure fixes required to reduce water damage remain out of reach in the short term.  

“Parts of Montreal require significant, long-term fixes that would be very capital-intensive, and these don’t happen in a year. It will take some time before we start seeing a difference being made there,” he says.  

Many older homes have combined drainage systems, where sewage and stormwater leave homes via the same pipe, he explains. New homes, in comparison, would have two separate lines — one for sewage and one for stormwater — that would lead to two separate pipes under the street.  

“Switching systems from old combined systems to new separated systems is a very expensive and disruptive process,” McGillivray says. “Additionally, many homes and low rises in Montreal have reverse slope driveways, where there are garages located under homes (i.e. the sidewalk is higher than the lowest part of the driveway).

“We see many basements flood as a result of these relics from a time past.” 

Alyssa DiSabatino

Alyssa Di Sabatino has been a reporter for Canadian Underwriter since 2021, covering industry trends, market developments, and emerging risks.