Changing Hydrological Regimes

Since the pre-industrial era, the average annual temperature in Quebec has risen by between 1 and 3°C and this trend is expected to continue. Temperatures changes alter the water cycle and can affect a number of hydrological parameters (precipitation, snow and ice melt, evapotranspiration, etc) that have a direct bearing on the probability of occurrence of different types of floods.

Types of Flooding in Quebec

Freshwater flooding occurs when rivers spill over their banks because they have too much water to drain. This type of flood generally coincides with the spring snow melt, but may also occur in summer or fall following extreme precipitation events. 

Ice jam floods occur when an accumulation of floating or frazil ice in a river creates a sort of temporary dam, causing the watercourse to spill over its banks farther upstream.

In urban environments, sewer backups often occur following extreme precipitation events, which can lead to significant flooding.

Coastal flooding refers to an inundation of the coastal environment by the sea. It occurs during sea storms and is exacerbated by rising sea levels and the decline in ice cover along the coasts. 

Generally speaking, watercourses in southern Quebec will be subject to more frequent winter thaws, while shorter winters will mean a significantly earlier arrival of spring floods across the province. These events will occur one to two weeks earlier by mid-century and two to three weeks earlier by the end of the century. 

It is also expected that precipitation in the form of rain will increase in winter and spring and that extreme rain episodes will become more intense in summer and fall. By integrating these changes into probability studies of freshwater flood discharges, certain trends in Quebec can be discerned. Firstly, it is anticipated that spring flood volumes will be higher north of the St. Lawrence Valley and lower in extreme southern Quebec, though for many rivers this trend remains uncertain. Also, it is expected that peak summer and fall flooding will be higher across a large swath of southern Quebec. The future evolution of river discharges will vary greatly as a function of diverse parameters such as watershed size, river location, land use, seasons, etc. 

Sewer backups will be exacerbated by the uptick in extreme precipitation events in summer and fall, especially in urban settings where runoff is greater due to the impervious nature of ground surfaces.


Every year, ice jams in Quebec’s rivers generate sudden, unexpected and intense flooding that test the capacities of the province’s public security services. This type of flooding is generally unpredictable and often appears chaotic, as its occurrence depends on the interaction of multiple meteorological, hydrological, ice and morphological parameters. The impact of climate change on this type of flooding has been studied in some of Quebec’s rivers. The results vary widely from one river to another but show that, overall, ice jam flooding will cause greater destruction in the future. Our understanding of how this hazard is evolving with climate change is still in its infancy, but is expected to improve in the years to come.

Figure 2

Figure 2 : Hazard × Vulnerability = Risk (MELCC)


In the context of disasters such as floods, risk represents the combination of i) the presence of a hazard and ii) the vulnerability of the territory and the society exposed to the said hazard. Together, these components influence the possibility that negative effects will occur. Therefore, it is not merely fluctuations in the hydrological cycle that determine the risk of a natural disaster, but also how humans and property are distributed across a flood plain. Now more than ever, land use decisions represent a major issue in the evolution of flood risk in Quebec, which is having to reconcile with demographic growth and urban development factors. In fact, the impacts of flooding are increasingly costly, which is in large part attributable to a growing exposure of our assets, higher values of real and personal property, and a poor understanding of risk.

Photo : https://agrcq.ca/

Impact of Flooding on Society

Even if floods in Quebec are not particularly deadly, their immediate impacts are manifold. Floods can cause material damage and disrupt essential services. For example, they can lead to interruptions in the drinking water supply, power and telecommunication outages, inaccessible roads and disruptions to healthcare services. Flooding may also affect certain economic activities, for example by destroying cropland. Businesses may sustain flooding and be forced to suspend their activities.  

Additionally, floods can have impacts on the mental and physical health of those affected. They cause serious disruptions to the lives of exposed citizens and are associated with a higher risk of symptoms or disorders related to post-traumatic stress, anxiety and a significant feeling of long-term insecurity. At the physical level, floods may notably cause injuries, drownings, automobile accidents on flooded roadways or the aggravation of pre-existing chronic illnesses. A multitude of socioeconomic characteristics such as living alone, having a low income, falling into a certain age bracket, having recently immigrated, or being unable to communicate in French or English can exacerbate the consequences suffered by flood victims.

Photo : Canadian Red-Cross


Recent decades have been marked by a series of flooding disasters with substantial consequences in a number of communities in Quebec. These events caused material damage both to public infrastructure (e.g. roads, bridges, aqueducts, schools, hospitals, telecommunication networks, etc.) and private property (e.g. residences, yards, furniture, automobiles, objects, etc.). In 2017, spring flooding affected over 5,300 residences and damaged some 400 roads throughout Quebec. 

Considering government expenditures only, it is estimated that between 1991 and 2013, average annual flood-related costs were in the order of approximately $70M; however, the floods of 2017 and 2019 caused these figures to skyrocket to $360M and $438M, respectively, according to Quebec’s Ministry of Public Security. Additional costs are inevitably borne by the flood victims themselves, regardless of any financial assistance offered or possible insurance claims. On top of this are indirect costs related to the loss of economic activities and impacts on the victims’ physical and psychological health.

Figure 3

Source : Canadian Climate Institute

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