Heavy rainfall is expected to sweep across Ontario and Quebec starting tonight, placing several rivers already swollen by spring runoff under intense surveillance. Authorities warn that these new precipitations will hit regions already struggling with flood levels.
Regions Under High Alert
Minor and moderate flood thresholds have already been reached in several areas, including the Laurentides, Lanaudière, Mauricie, Centre-du-Québec, and Outaouais regions. Luc Bourassa, spokesperson for the Quebec Ministry of Civil Security, noted that three rain systems have already crossed the province since April 13.
A fourth system is currently arriving from the west, bringing an expected 15 to 25 mm of rain to Ontario and Quebec. Environment Canada predicts 10 to 20 mm for the Outaouais region, while the Laurentides and Lanaudière could observe 15 to 25 mm, which may lead to considerable accumulations.
Critical Risks in the Outaouais Valley
Philippe Gachon, a professor of hydroclimatology at UQAM and director of the Réseau Inondations InterSectoriel du Québec, suggests the situation may be most critical in the Outaouais Valley. He warns that water levels could reach heights comparable to those seen during the major floods of 2017.
The risk is compounded by heavy snowpacks in Abitibi, where depths of 50 to 60 cm remain in some areas. The combination of rapid snowmelt and new rain is likely to put extreme pressure on rivers that may lack the capacity to absorb the surplus.
Specific concerns have been raised regarding the Gatineau and Coulonge rivers. Gachon suggests that because flow is already very high at the Carillon station, Hydro-Québec may be forced to open the hydroelectric dam.
Urban Centers on High Alert
The City of Montreal has transitioned to its third and final alert level for emergency flood measures. The region is preparing for the arrival of large volumes of water flowing from the Outaouais River.
In Quebec City, the Saint-Charles River is already overflowing, specifically in the Duberger sector. Inundations could occur Sunday morning due to a combination of 10 to 25 mm of rain, high tides, storm surges, and strong winds.
Environment Canada has issued a storm surge warning for the coastline of the Capitale-Nationale region. Residents are advised to avoid low-lying areas and refrain from driving on flooded roads, as saturated soil has a reduced capacity to absorb further rain.
Long-Term Hydrological Shifts
Professor Gachon indicates that these risks reflect a broader trend linked to climate change, which is altering hydrological regimes and the balance between rain and snow. He observes increased runoff and water input in the Outaouais Valley.
Because warming is occurring faster than previously anticipated, Gachon argues that municipalities must revise their development plans. He suggests that flood maps must be updated with the support of the Quebec government, particularly for smaller municipalities with fewer resources.
A potential reprieve may arrive in the coming days as temperatures are expected to drop. This cooling could slow the snowmelt, which Luc Bourassa says would provide rivers a chance to evacuate the current surplus.
Frequently Asked Questions
Which regions are currently most at risk of flooding?
The Laurentides, Lanaudière, Mauricie, Centre-du-Québec, and Outaouais regions have already reached minor or moderate flood thresholds. The Outaouais Valley is considered the most critical area.
What specific factors are threatening Quebec City this Sunday?
Flooding in Quebec City may be caused by a combination of 10 to 25 mm of precipitation, strong winds, a storm surge, and a high-amplitude tide.
Why is the situation in Abitibi contributing to the flood risk?
Abitibi still has significant snow accumulations, reaching 50 to 60 cm in some places. The rapid melting of this snow, combined with new rainfall, increases the volume of water entering rivers that may not be able to absorb it.
How prepared are your local community’s drainage systems for unexpected spring surges?
