Heavy rain: A new climate reality 

Globally, we are facing a new climate reality characterized by increasingly extreme weather events, including more frequent episodes of very intense rains that cause significant damage. This is a trend that is expected to increase in the coming years.  

Several solutions exist to make our cities more resilient. In Montréal, along with other innovative cities, we can collectively adapt to increase our resilience to torrential rainstorms and significantly reduce the impacts on the community and its infrastructures.  

Montréal is a large urban area that is heavily mineralized and where rainwater rarely infiltrates the ground. Traditionally, sewer systems were designed to manage storm water. Today, no one system on its own can manage these torrential rains, which have become commonplace. Conventional solutions based on oversizing sewer systems are not sustainable because there will always be rainfall that is greater than the capacity of the system, not to mention the costs and technical challenges of these solutions.  

We need to take a more comprehensive approach that focuses on the resilience of our land and our built environment. The need to adapt and the actions to take involve the entire population. 

Features of torrential rains 

Heavy or torrential rain is a severe weather event that involves substantial rainfall over a limited area in a very short time. This causes sudden overflows of the sewer system and accumulations of water on the street that can spill over into buildings and sensitive infrastructures, causing significant damage. Flood risks also increase, damaging infrastructure and buildings.  

What is resilience and adaptation? 

Urban resilience refers to the ability of people, communities, institutions, businesses and systems within a city to resist, adapt and develop while considering long-term ecological, social and economic challenges. 

To achieve urban resilience, it is essential to adapt. It means accepting change and finding new ways of doing things so that we can live in this new reality while minimizing its impacts. Montréal, like all major cities, wants to adapt in order to increase its resilience to climate change, particularly with respect to torrential downpours.  

For example, rather than flooding streets and buildings, the city seeks to direct water runoff to lower-risk areas, such as parks or green infrastructures during extreme rainfall. These developments are not only inexpensive, but also offer side benefits, such as reducing heat islands or increasing biodiversity. 

A collective action plan 

There are several measures to take. The challenges in terms of storm water management in the context of climate change require shared solutions that involve the entire community – the city, the population, associations, companies and governments. 

This is why Montréal has set out a clear and innovative vision and guidelines through its action plan for flood resilience during heavy rains (in French). This plan is based on coordinated efforts towards a common goal. It puts forth both actions to help building owners and actions to improve and adapt water management systems. It has three parts and 10 key measures. 

PART I: SUPPORTING OWNERS IN THE PROCESS OF ADAPTING THEIR BUILDINGS  

Part 1 of the action plan focuses on helping owners of residential buildings affected by flooding during heavy rains. This assistance can take several forms, including financial and technical. 

Measures 

• Enhance the subsidy program to reduce adaptation costs for flood-affected homeowners 

• Amend city by-laws to facilitate adaptation of existing buildings 

• Provide advisory support to homeowners with regards to reducing the vulnerability of their building 

• Check the effectiveness of flood protection measures for homes with a counter-slope garage entrance.  

You can find more information about which actions to take to protect a private building.    

PART II: FOCUSING ON PREVENTION BY ADAPTING BY-LAWS  

Part 2 of the action plan aims to amend urban planning by-laws to ensure that the new built framework is resilient to the risk of flooding by preventing the creation of new vulnerabilities.   

Measures 

• Include provisions to prohibit sensitive land uses in sectors that are vulnerable to flood risk in the 2050 Land Use and Mobility Plan 

• Amend the city’s By-law concerning the construction and conversion of buildings to take materials and measures to make buildings flood resistant into account 

PART III: CONTINUING ACTIONS TO IMPROVE PUBLIC INFRASTRUCTURES  

Part 3 of the action plan aims to strengthen the municipal response to extreme climate events. This includes expanding water retention capacity in sewer systems, creating surface retention capacities and establishing contingency plans to increase flood resilience during torrential rains.   

Measures 

• Ensure that public development projects are resilient by default, such as resilient parks 

• During reconstruction or repair projects, change street design to direct surface drainage to resilient public spaces whenever possible 

• Identify key vulnerable points, such as a water main underneath a major street near a hospital, and develop a bypass road plan during heavy rain  

• Prioritize investments and responses to improve the drainage system in problematic areas 

Some measures are currently being rolled out and you can learn more about actions the city is taking to adapt to torrential rains.