Recent storms and heavy rain
Updated September 28, 2026
This page sums up recent storms and heavy rain in Québec, at sector level, with their sources. For each one, it states what the sources report about where the water came from: surface runoff, sewer backup, a river or stream, or groundwater.
Runoff or sewer backup?
Runoff is rain flowing over the ground and collecting in low spots, from where it can get in through a basement window or a garage door. Sewer backup is water from the sewer network coming back into the house through the basement drains; for that risk, ask a plumber about a backwater valve. The check simulates surface runoff around an address; it does not say whether or how water gets into a building.
Recent events
Areas: Dollard-des-Ormeaux and Pierrefonds-Roxboro (West Island of Montréal)
A nearly stationary storm cell dropped 100 to 170 mm of rain in about an hour on parts of Dollard-des-Ormeaux, according to the City, beyond what the Centennial Lake retention pond normally handles. Authorities asked residents to limit water use to protect basements. In Pierrefonds-Roxboro, in a sector outside any recognized flood zone according to La Presse, the borough mayor said groundwater came up through foundation cracks.
Mechanism not stated in the sources. The sources do not make it possible to tell runoff from sewer backup. Sources also report groundwater seeping in, which the check does not cover.
Sources: Ville de Dollard-des-Ormeaux, foire aux questions · Radio-Canada (2026-06-21) · CBC News (2026-06) · La Presse (2026-06-22)
Areas: Saint-Constant, Delson, Sainte-Catherine and Candiac (South Shore)
According to Delson's mayor, nearly 150 mm of rain fell in a few hours: the storm-sewer network was overloaded, but the sanitary network worked. Environment Canada had warned that slow-moving storms would probably cause flash floods, as the ground had a reduced capacity to absorb rain. Saint-Constant declared a local state of emergency and told residents hit by flooding or sewer backup to call their insurer. The rivière de la Tortue also overflowed its banks (river flooding).
Runoff and sewer backup. The check covers the runoff part, not the sewer backup. Sources also report a river or stream overflowing, which the check does not cover.
Sources: Ville de Delson (2026-06-21) · Ville de Saint-Constant, état de la situation · Ville de Saint-Constant, état d'urgence local · Le Reflet (2026-06) · Radio-Canada (2026-06-21)
Areas: Montréal (Saint-Laurent, Ahuntsic-Cartierville, Saint-Léonard, Villeray, Saint-Michel), Saint-Eustache, Mirabel and Sainte-Thérèse
About 100 mm of rain fell on the metropolis in under three hours, according to Radio-Canada; Environment Canada measured 81.6 mm at Montréal-Trudeau airport for the day. Sewers filled quickly and backed up into the basements of many homes, and water flooded businesses, parking lots, streets, interchanges and highway ramps. In Saint-Léonard, La Presse describes a sector in a cuvette (a low-lying basin) where driveways slope down to lower garages or basements; some residents there were flooded for the second time in twelve months.
Runoff and sewer backup. The check covers the runoff part, not the sewer backup.
Sources: Radio-Canada (2025-07) · ECCC, station Montréal-Trudeau (2025-07-13) · La Presse (2025-07-13)
Areas: Montréal, Laurentides and Montérégie
The remnants of Debby left 154 mm of rain at Montréal-Trudeau airport, an all-time daily record according to Environment Canada, and 141 mm downtown. Underpasses flooded in several boroughs, according to the City of Montréal, and the water closed stretches of highways 15, 20 and 40. In Montréal, the Laurentides and Montérégie, many homes were flooded or had sewer backups. At the Dorval tunnel, the water reportedly built up after a sewer backup damaged the pumping system.
Runoff and sewer backup. The check covers the runoff part, not the sewer backup.
Sources: La Presse (2024-08-09) · ECCC, most impactful weather stories of 2024 · ECCC, station McTavish (2024-08-09) · Radio-Canada (2024-08-12)
Areas: Laval
According to the City of Laval, 125 to 200 mm of rain fell (radar estimate) between 9 a.m. and 9:30 p.m. during Debby. The City lists three kinds of flooding: runoff, storm-sewer backup and overflow of streams within the city. According to its technical report, the areas with the most claims lie mostly in cuvettes (low-lying basins), where a reverse-slope garage driveway raises the risk. Most of the affected buildings are connected to sewer networks built between 1960 and 1982.
Runoff and sewer backup. The check covers the runoff part, not the sewer backup. Sources also report a river or stream overflowing, which the check does not cover.
Sources: Ville de Laval, rapport sur la tempête Debby · Ville de Laval, rapport technique Debby (2025-05-20)
Areas: Vaudreuil-Dorion
During Debby, Vaudreuil-Dorion got 219 mm of rain in 20 hours, according to the City. Several streets became impassable, a street caved in and there was a landslide. The City later held a public information session to explain how sewer backup and surface flooding happen. The then-mayor said sewer backups are more frequent in some parts of the city, and that power outages that evening also caused flooding in some neighbourhoods.
Runoff and sewer backup. The check covers the runoff part, not the sewer backup.
Sources: Ville de Vaudreuil-Dorion, mesures d'urgence · Néomédia Vaudreuil-Soulanges (2024-09-04)
Areas: Bois-des-Filion (North Shore)
According to the City of Bois-des-Filion, about 175 mm of rain fell during Debby, an abnormal amount that exceeds what a normal storm-sewer network can take. The City then organized a special pickup of debris and waste from sewer backups in homes.
Sewer backup. The check does not cover sewer backup.
Sources: Ville de Bois-des-Filion, informations pour les sinistrés
Areas: Terrebonne and Mascouche (North Shore)
During Debby, close to 160 mm of rain fell in a few hours on Terrebonne and 171 mm on Mascouche, according to the two cities. In Mascouche, according to the mayor's estimate reported by La Presse, the Rivière Mascouche overflowing reached only a small share of the flooded owners; the article does not say how water got into the other homes. Terrebonne said at the end of 2025 that an analysis of the affected areas, to pin down the probable causes of the flooding, was under way.
Mechanism not stated in the sources. The sources do not make it possible to tell runoff from sewer backup. Sources also report a river or stream overflowing, which the check does not cover.
Sources: Ville de Terrebonne, bilan 2025 de la Stratégie bleue · Ville de Mascouche, plan de résilience climatique 2026 · La Presse (2024-08-22)
Areas: Greater Montréal
The remnants of Hurricane Beryl brought thunderstorms and torrential rain: 79.2 mm at Montréal-Trudeau airport and 59.3 mm at the McTavish station downtown for the day, according to Environment Canada. Muddy water flooded streets, underpasses and the Décarie Expressway, where motorists were stranded. Stretches of highway were closed because of standing water. Sewers backed up across the city, and basements, garages and businesses flooded.
Runoff and sewer backup. The check covers the runoff part, not the sewer backup.
Sources: Radio-Canada (2024-07-11) · ECCC, most impactful weather stories of 2024 · ECCC, station Montréal-Trudeau (2024-07-10) · ECCC, station McTavish (2024-07-10)
Areas: Montréal
Violent thunderstorms hit Montréal. The McTavish station downtown recorded 81.7 mm of rain, against 38.6 mm at Montréal-Trudeau airport. Drivers were stuck in flooded underpasses, and within a few hours the City received many 311 calls about sewer backups, blocked catch basins or broken branches. According to Environment Canada, repeated storms overloaded municipal sewers in Québec, and July 2023 was the wettest July at the airport since records began there in 1941.
Runoff and sewer backup. The check covers the runoff part, not the sewer backup.
Sources: La Presse (2023-07-13) · ECCC, station McTavish (2023-07-13) · ECCC, station Montréal-Trudeau (2023-07-13) · ECCC, top weather stories of 2023
The check does not replay any of these storms: it drops a 100-year, one-hour design storm on the ground around one address and shows where the water collects.
See where a heavy storm's water collects around an address
Enter a house's address, pay $39 once and get by email the peak depth of rain water on the lot and where it collects around it.
Elsewhere on this site
These summaries describe past events at the sector level, based on public sources. The FloodVerity check is a rain screening for one address, not a hydraulic study; it covers neither river and lake flooding nor sewer backup.