Higher temperatures not only make daily life uncomfortable, they can also be life-threatening. In 2018, an extreme heat wave in Montreal led to 66 deaths over six days, with those living in areas heavily affected by the urban heat island effect facing twice the risk of death.
Before the first heat wave hits next season, some neighbourhoods are taking preemptive steps to cool down the concrete jungle.
The Plateau announced on March 27 that it's digging 200 sidewalk pits to plant trees along roads and sidewalks. The initiative cites increasing greenery to lower local temperatures, improve air quality, and enhance the overall livability of the area.
On March 28, the city also unveiled plans to expand city gardens, opening up 300 new community gardening spaces across 14 boroughs. Around 8,500 green-thumbed Montreal residents will benefit in Côte-des-Neiges-Notre-Dame-de-Grâce, Rosemont–La Petite-Patrie, South West, Mercier-Hochelaga-Maisonneuve, Rivière-des-Prairies-Pointe-aux-Trembles, Saint Laurent, Ville Marie, Ahuntsic-Cartierville, Anjou, and Verdun.
The plans include the renovation of existing gardens like Cabrini Annex and the development of new ones like Deschamps North, Vertical Installation, and Rosemont Library gardens.
"Greening the city and fighting against heat islands is a concrete response to the complex issues of protecting biodiversity," said Marie-Andrée Mauger, the executive committee member responsible for ecological transition and the environment.
Seeds of change
A 2023 study revealed that covering 30% of urban space with trees and plants can mitigate temperatures by up to four degrees, counteracting much of the heat island effect.
While a reduction of four degrees may seem modest, the study, led by the Barcelona Institute for Global Health, found that over four percent of summer fatalities in European cities were linked to the slight elevation in temperatures induced by urban heat islands. Risks of dehydration, sunstroke, or cardiovascular disease all escalate in cities and can be mitigated with sufficient tree-planting initiatives.
Trees and plants also act as natural filters, purifying the air by trapping pollutants like carbon dioxide and nitrogen dioxide.
A map of Montreal heat islands based on data from July 6, 2023.Courtesy of the city of Montreal and UQAM.
The heat is on
In Montreal, the temperature divide is stark. Downtown Montreal and other densely populated areas, especially those with a lot of concrete, often feel the heat more intensely than the greener, less crowded neighbourhoods.
An interactive heat island map by Montreal’s Bureau of Ecological Transition and Resilience and UQAM’s Department of Geography shows the growth of heat islands over time. The latest satellite data from July 2023, recorded during a heat wave, shows the western end of the island was less prone to the urban heat island effect, due in part to lower population density and higher tree cover. Central and eastern parts of the island, on the other hand, are marked by higher population density and fewer trees, making them more vulnerable to the urban heat island effect.
The greenest parts of the map show tree cover and green spaces that stay at cooler temperatures even on the hottest days. As of 2022, Montreal began installing temperature and humidity stations to study urban heat over the next decade, with plans to add 200 more through 2024.
In keeping with Montreal's Climate Plan 2020-2030, the city is working toward a 55 percent reduction in greenhouse gas emissions (from levels in 1990) within the next decade, with the ultimate goal of achieving carbon neutrality by 2050. Initiatives are underway to convert parking lots into open spaces, plant half a million trees, promote public transport, and implement a zero-emissions zone downtown.
While the latest push for sidewalk tree planting and community gardening this year will help curb the urban heat island effect in Montreal, the city's broader plan to combat climate change is what really holds the key to a cooler tomorrow.
What is an urban heat island?
Montrealers walk under a misting system to cool off during a heatwave in Montreal's Quartier des festivals.
Marc Bruxelle | Dreamstime
An urban heat island is a literal city "hot spot" where temperatures soar, creating health risks and amplifying the effects of global warming. These areas often see elevated temperatures due to dense populations, extensive energy use, and a lack of green spaces, leading to increased energy dissipation. It's like the process of charging a phone, where energy from the wall flows into a device, producing light, sound, and of course, heat.
The principle that "energy cannot be created nor destroyed" lays the groundwork for understanding urban heat islands by highlighting how energy within a city's environment is continuously converted and transferred, rather than disappearing.
In the context of urban heat islands, vast amounts of energy consumed by buildings, vehicles, and industrial processes are transformed into heat, which is then emitted into the surrounding environment. Unlike in less developed areas, where the natural landscape can absorb and dissipate this heat more effectively, the dense infrastructure of cities traps and accumulates it. The process is exacerbated by the materials commonly used in urban construction, like asphalt and concrete, which absorb and retain heat more efficiently than natural surfaces. These materials also have low reflectivity or albedo, meaning they absorb a higher proportion of the sun's energy and convert it into heat, further warming the urban environment.
The dark, paved surfaces in cities that trap heat are akin to how dark clothing absorbs more sunlight and gets hotter compared to light clothing. Urban green spaces and trees help counteract the heat island effect by increasing the area's overall reflectivity, reducing the heat absorbed, and helping to lower temperatures in urban settings.
A map of Montreal heat islands based on data from July 6, 2023.
