Extreme rainfall
In Quebec, extreme rainfall particularly affects the south of the province and the coastal regions. Some of the main impacts are high water levels and pluvial flooding, soil erosion, and reduced water quality.
These impacts can also have consequences for :
infrastructure
public health and safety
natural environment
economy
Essential infrastructure and services
Extreme rainfall is one of the leading causes of deterioration of public and private infrastructure, including:
Buildings (exterior and interior)
Roads
Rainwater and wastewater drainage systems
Bridges
Culverts
Certain characteristics of urban environments make them more vulnerable to heavy rainfall events, especially those that occur in a short period of time. Combined sewers in several Quebec municipalities carry both wastewater and rainwater to treatment plants. When it rains heavily and there is a sudden increase in flow, the carrying capacity of this type of system can quickly be exceeded, leading to a risk of overflow.
Urban environments are often covered by mostly impervious surfaces like concrete and asphalt. Unlike natural environments, these surfaces do not allow water to be absorbed by the soil, which encourages its accumulation and faster runoff.
This phenomenon is particularly problematic in areas prone to water accumulation, such as:
Roads with inadequate grading
Garages with a reverse slope driveway
Underground residential, commercial and transportation infrastructure
Natural environment
Heavy rain and the floods it causes have consequences for natural environments and biodiversity.
Biodiversity
Runoff from extreme rainfall carries large amounts of soil particles to the shores of freshwater and marine ecosystems. This phenomenon is amplified in areas where the land use type encourages it, as is the case with agriculture, urbanization and deforestation.
Excessive sediment and nutrient input contribute to the eutrophication of water bodies, a process that promotes the growth of algae and cyanobacteria. These can outcompete other aquatic species, disrupting the balance of ecosystems and affecting the species that live in the body of water or depend on it.
The life cycle of many insect species is strongly linked to seasonal and environmental variations. More intense and frequent rainfall during a species’ larval stage may reduce its chances of survival. Similarly, the daily activities of some species, such as foraging by pollinating insects, can be disrupted if it rains more frequently at certain times of the day.
Natural environments
Extreme rainfall can cause other climate-related events that damage natural environments gradually or suddenly, such as landslides and coastal erosion and submergence. These hazards can destroy habitats on the coast or on slopes.
Health, safety and well-being
The various effects of extreme rainfall on the built and natural environment have numerous impacts on the health, safety and well-being of populations.
Physical impacts and illnesses
Flooding caused by extreme rainfall can cause various injuries, as well as risks of hypothermia and drowning. The risks of electrocution, cuts, and other injuries rise during the event and the recovery period due to weakened structures and the increased use of dangerous tools. They also increase the risk of carbon monoxide poisoning due to the use of generators and backup heating or cooking appliances during power outages.
Extreme rainfall can promote the spread of disease. Poor water quality increases the risk of gastrointestinal illnesses through the transmission of pathogens such as viruses, bacteria and parasites. Temporary pools of water allow the proliferation of mosquitoes, which are potential vectors of diseases like the West Nile virus. And buildings that are poorly protected, maintained, or cleaned following a flood are likely to quickly develop mould problems. These can lead to respiratory problems like asthma, as well as allergic reactions.
Psychological distress
Material losses, the costs incurred and the uncertainty resulting from the impacts of extreme rainfall affect the psychological states of people whose homes are flooded. These effects are even more pronounced when there is a lack of social and financial support. Symptoms of post-traumatic stress disorder are common among people exposed to flooding, as well as first responders.
