Flood-proofing our future

October 21, 2024

The high cost of flooding

Thirty-six catastrophic floods have hit Canada in the past 11 years. In 2013, two major rain storms hit Calgary, Alb. and Toronto, Ont., causing $6 billion and $1 billion in damages respectively. In 2024, flash flooding in southern Quebec and Toronto caused $2.5 billion and $940 million in damages. The frequency and severity of these events are rising due to climate change, with projections showing that flooding alone will cost the Canadian economy $30 billion by 2050. The price of inaction is far too high. Fortunately, there is a cost-effective way to mitigate future flooding events: nature-based solutions (NbS).

Why are Canadian cities prone to flooding?

The short answer: Water can’t flow through concrete, and cities are concrete jungles.

Forests, wetlands, rivers and marshes are powerful natural drainage systems. Most Canadian cities have replaced them with parking lots, buildings and roads. This increases the risk of flash flooding because concrete surfaces cause water to gather quickly. During heavy rainfall and annual spring thaw events, water flows are directed into sewers rather than soils. Sewers can quickly reach capacity and overflow.

Nature-based solutions: A cost-effective way to adapt to flooding

Investing in nature-based solutions is a fundamental part of any successful flood protection strategy. Constructed and restored wetlands, green roofs, sponge parks/bioswales (landscaped basins that hold water), help avoid flooding by absorbing stormwater that would otherwise easily overwhelm constructed drainage systems. Beyond flood mitigation, NbS offer a range of additional benefits. They increase carbon sequestration, support wildlife, improve health outcomes and advance meaningful efforts for reconciliation (NbS are intertwined with Indigenous wellbeing).

The financial advantages of NbS are significant. For every dollar invested in adaptation, there is a $20 CAD return in direct and indirect benefits. When used alongside traditional infrastructure like dams and sewers, these solutions can cut flood damage costs in half. It is estimated that natural wetlands reduced the damages from Hurricane Sandy by $848 million CAD. Marsh restoration can prevent $1.2 million CAD of damage caused by flooding per hectare, increasing to $12.5M/ha as climate change worsens. Green roofs can reduce flood volume by up to 62% and reduce runoff volume by 24%.

In short, it costs far less and saves us millions if not billions to conserve and restore natural landscapes to help mitigate flooding than to pay the high price of rebuilding after a flood.

Building flood resilience with nature

Case study: Port Lands Flood Protection Project

In 2017, Waterfront Toronto, Toronto and Region Conservation Authority (TRCA), and the City of Toronto launched an ambitious $1.25 billion-project to restore the mouth of the Don River. This initiative will enhance flood protection for 240 hectares of downtown waterfront, and promote community wellbeing. It is expected to contribute $4 billion to the Canadian economy, while reducing a portion of the projected $30 billion in flood damages by 2050.

Case study: Ralph Klein Park

Ralph Klein Park is a constructed wetland in Calgary, Alb. that stores and filters stormwater runoff. Storing over 6 million cubic meters of water, the wetland has enough capacity to handle a major 1-in-100 year flood. Other benefits of the park include a community playground, a LEED Platinum-certified education center and habitat for 46 species of birds.

Next steps

While NbS are a proven, cost-effective way to reduce flooding and mitigate climate change, these strategies are far from being universally accessible. Here are three key actions to help accelerate greater adoption across the country:

Government can help municipalities prevent floods by:

applying and/or bringing back mandates to give more funding to Conservation Authorities at the TRCA
developing frameworks (such as the Quebec Water Strategy 2018-2030) that financially support municipalities to improve their disaster preparedness
collaborating with charity groups to increase resilience capacity

Implement watershed level land-use planning: NbS and flood preventative gray infrastructure should be implemented in accordance with the natural watershed, as opposed to city boundaries.

Conserve existing green spaces: Conservation is the most cost-effective way to obtain ecosystem benefits. Ontario's Greenbelt provides $224 million in flood protection to the region each year.

As flooding events grow more frequent and severe due to climate change, it's clear that the cost of inaction is unsustainable. Nature-based solutions offer a proven, cost-effective path forward, protecting our cities while enhancing ecosystems and community well-being. By investing in these strategies today, Canada can mitigate future flood risks and reduce economic losses — while reaping the many additional benefits that nature provides. The time to act is now.