High water and flooding
In the medium to long term, the effects of climate change are likely to change the occurrence and intensity of high water events in the province. Projections indicate that Quebec’s rivers will change. In winter and spring, warming temperatures and increased precipitation in the form of rainfall are likely to influence water levels. In summer and autumn, flooding is likely to be modified by increased extreme precipitation.
Springtime high water events
Earlier peak water levels: By 2050, the day when the peak water level occurs, i.e., the maximum flow value observed, is expected to be earlier. It could occur 9 to 14 days earlier by mid-century. By 2080, it could come 15 to 24 days earlier. This change is greater for basins further south in the province.
Figure 2 : Average day of occurrence of the maximum daily flow in winter and spring in 2071-2100 in a high GHG emission scenario (RCP 8.5) compared to the historical period 1981-2010. Red represents a change of more than 24 days, while orange represents a change of 14 to 24 days compared to normal. (From: Gouvernement du Québec, 2022)
Greater water volumes north of the St. Lawrence River Valley: Projections suggest that spring freshet volumes will be higher north of the St. Lawrence River Valley, while they could be lower in the far south of Quebec. However, a level of uncertainty persists for several rivers. The direction of change expected for these rivers varies from year to year depending on precipitation events, resulting in a lack of consensus.
Figure 3 : Direction of average flow over 14 days in winter and spring for a 20-year high water event in the future period 2071-2100 based on the RCP4.5 GHG emission scenario, compared to the historical period 1981-2010. Blue represents an increase in flow, while red and orange represent a decrease. White represents the uncertainty. (From: Gouvernemnt du Québec, 2022).
Summer and fall flooding
Climate change will likely lead to an increase in summer and fall high water events throughout Quebec. The magnitude of this increase varies depending on the time horizon considered and the greenhouse gas emission scenario used. However, current projections indicate that water volumes and peaks in summer and fall will be greater. It should be noted that high water events in the summer and fall are less often associated with flooding.
Figure 4: Maximum daily flow in summer and fall for a 20-year flood in 2071-2100 based on an RCP8.5 GHG emission scenario, compared to the historical period 1981-2010. Dark blue represents an increase of more than 25% in the maximum flow of a watercourse. (From: Gouvernement du Québec, 2022).
Winter flooding
In winter, watercourse flows are generally lower due to freeze-up. However, winter flows are likely to increase due to projected warming during this season and the resulting melting of river ice.
Return to the observed changes
Consult the impacts of high water and flooding
