1.4K 
Throughout April UrbanToronto is featuring a special State of Environment editorial series to explore critical sustainability issues across our region.
* * *
On July 16, 2024, Torontonians were going about their day as the skies darkened above them, unaware of the scale of the deluge that was approaching. Within the span of about three hours more than a month's worth of rain — 97.8mm at Pearson and more than 100mm in other areas — was dumped on the city, leaving many stranded, soaked, and without power as the region's waterways breached their banks and the sewers backed up, unable to handle the quantity of water that fell from the sky. Highways were blocked by rising water, subway tunnels and underpasses were flooded, and many basements across the city were filled with stormwater that had nowhere else to go. It is estimated that the storm cost the city roughly $1 billion in insured damages.
This is not the first time in recent memory such devastating floods overtook the city. In August 2018, two men were dramatically rescued from a flooding elevator when the city was inundated with a similar torrential downpour, and images of a stranded streetcar filled with waist-high water below the King-Dufferin underpass highlighted the severity of the flooding. In July 2013, Toronto experienced a storm worse than the 2024 downpour, dumping 126mm of rain across the city and breaking Toronto's all-time single-day rainfall record that was previously set by the infamous Hurricane Hazel in 1954 (the all-time record was actually broken again on August 17, 2024 when 128.3mm were recorded at Pearson Airport that day, which currently stands as the rainiest day in Toronto's history). Another vicious storm brought the region to a grinding halt in August 2005, best known for opening a giant sinkhole at Finch and Sentinel and bringing several tornadoes with it across Southern Ontario.
Flooding has been identified as the greatest natural disaster risk for the City of Toronto in the face of climate change, alongside extreme heat. The frequency of major flooding events is increasing, and the city's infrastructure is simply not designed to handle it. The benchmark of a "100-year storm" is typically used to measure resiliency of the city's infrastructure, which is defined as an extreme rainfall event that brings around 115mm or more of rain within 24 hours, and which has a 1% statistical probability of happening within any given year based on historical weather data. There have been at least five of these events within the past 20 years, two occurring in 2024 alone.
As climate change brings more extreme weather, all three levels of government have been taking steps to increase the resiliency of our built environment and to protect our city in the face of more frequent flooding. These range from large-scale multi-billion dollar infrastructure projects, to regulations for new developments baked into the planning approvals process, to government subsidies for homeowners to flood-proof their properties.
The City has been targeting the most at-risk areas along waterways for infrastructure upgrades related to flood protection. The Toronto Region Conservation Authority has an interactive map that identifies all the flood plains across the GTA, which are any low-lying areas that are most at risk of flooding due to nearby waterways breaching their banks during a 100-year storm event. There are some surprisingly substantial areas of the city that are at risk, including southern Riverdale and Leslieville at the mouth of the Don River, and neighbourhoods along Black Creek.
Perhaps the most well-known flood mitigation project is the naturalization of the mouth of the Don River, which broke ground in 2019 and is now nearing completion in the Port Lands. Prior to this massive project, the Don River ended at an abrupt 90-degree angle bounded by concrete walls on both sides through the Keating Channel as it flowed into Lake Ontario, a legacy of the waterfront's industrial past. This unnatural bottleneck backed up the river during major rainfall events and led to flooding of the surrounding areas a good way up the Don Valley. The naturalization project moved millions of cubic metres of earth to create a new path for the mouth of the river, which now passes through more natural wetlands along its meandering route to the lake. In addition to significantly reducing the flood risk at the mouth of the Don, this has also unlocked huge tracts of land for new development on Ookwemin Minising (formerly Villiers Island) and beyond, and has given the city its newest green space, Biidaasige Park.
Prior to the Don River realignment, Corktown Common represented the first major flood protection project in the Lower Don Lands. Completed in 2014, the park is bordered by a large berm along its east and south edges, which is designed to be high enough to keep the Don River at bay and redirect the water into the lake if the river ever floods. Similar flood protection measures appear in early plans for the future East Harbour redevelopment on the opposite bank of the river.
Elsewhere in the city, federal funding was received in late 2025 to upgrade the sewer system for Black Creek and its tributaries, which for parts of its length notoriously runs through a concrete trench that dates back to the 1960s. Its current capacity cannot handle the heavy storms that are becoming more frequent. The infrastructure upgrades will increase the system's capacity to handle more stormwater and protect vulnerable neighbourhoods along its route from flooding, like Rockcliffe-Smythe and Oakdale-Beverley Heights. Further north, the City of Vaughan is doing its own stormwater upgrades to the Black Creek system to protect Vaughan Metropolitan Centre from flooding and to facilitate future development in the area.
Other flood mitigation projects are happening across the GTA, including in Brampton, where major work is now underway along the portion of Etobicoke Creek that runs through the downtown core. Included as part of their plan to revitalize downtown Brampton, the creek is being widened and deepened, several bridges are being rebuilt, and new parks and natural green space will eventually line the improved waterway.
Our buildings also play an important role in managing flood risk, and the Toronto Green Standard (TGS) includes mandatory requirements for stormwater management for all new major developments. The TGS mandates a minimum of 50% retention of total average rainwater to be stored on site, or an equivalent of 5mm from each rainfall event, which can either be reused in the building, returned to the ground after treatment through infiltration, or dissipated through evapotranspiration. This helps to prevent the city's stormwater infrastructure from being overwhelmed during heavy rainfall by redirecting or delaying some of the rainfall from entering the city sewer system, and also helps to reduce the building's overall water consumption.
The TGS also strongly encourages on-site green infrastructure, such as green roofs, planted landscaping, bioretention facilities, and reforestation where applicable. There is no better way to manage stormwater than with nature itself, and using plants and soil areas not only helps to store or delay stormwater before it makes its way into the sewer system or into the groundwater, but also provides natural filtration that removes pollutants for cleaner stormwater. Every little bit of greening on or around new or existing buildings helps ease the strain on the city's stormwater system, which in turn reduces the risk of flooding during major rainfall events. This approach is being adopted and has been used by many cities around the globe, as featured in our recent article about Montreal's flood risk mitigation.
At a more local scale, in 2025 the City of Toronto introduced the Basement Flooding Protection Subsidy Program, which provides homeowners up to $6,650 per household for eligible work to flood-proof their property. This subsidy can be used for a home plumbing assessment; installation of backwater valves; installation of a sump pump, alarm, and battery backup power; and, the severance and capping of a home's storm sewer or external weeping tile connection. The City's infrastructure is not designed to handle major storms everywhere in the city, and in anticipation of more frequent extreme weather they are helping homeowners to protect their properties during flooding events by contributing to home improvements. The subsidy program has been expanded in 2026 to cover more eligible works.
While the future of our climate is difficult to predict, it is certain that Toronto will be subjected to more frequent extreme weather events in the decades ahead. Given our location on the Great Lakes, the city's greatest vulnerability is with flooding, and so it is imperative that the resiliency of our urban infrastructure is prioritized in the face of a changing climate. Toronto's future is looking hot, humid, and wet, and we must do what we can to try to stay above water.
* * *
UrbanToronto’s new data research service, UrbanToronto Pro, offers comprehensive information on construction projects in the Greater Toronto Area—from proposal right through to completion stages. In addition, our subscription newsletter, New Development Insider, drops in your mailbox daily to help you track projects through the planning process.
* * *
* * *
Thank you to the companies joining UrbanToronto to celebrate State of Environnent Month.
