How Many Trees Would It Take to Cool Down Montreal?
- Natasha Dudek
- Aug 23
- 9 min read
As summers get hotter, Montreal is facing a growing threat from extreme heat. Asphalt and concrete trap warmth, creating an urban heat island effect that can make the city several degrees warmer than surrounding rural areas. Heat waves are among the deadliest climate hazards, and for cities like Montreal, an urgent question arises: how can we cool down an entire city?
Nature-based solutions are increasingly appealing for addressing urban challenges because they harness ecosystems to deliver multiple environmental, social, and economic benefits. Among these, tree planting is one of the most widely implemented strategies. By planting and conserving urban trees, cities can achieve substantial cooling through shading and evapotranspiration. For example, a 2024 meta-analysis led by researchers at the University of Cambridge examined 182 studies across 110 cities and 17 climate types worldwide and found that tree planting can reduce pedestrian-level temperatures by as much as 12°C, and reduce peak monthly temperatures to below 26°C in 83% of cities. Beyond regulating temperature, trees also improve air and acoustic quality, support physical and mental health, and help safeguard biodiversity.
Urban forestry guidelines are emerging to support greener, healthier, and more resilient neighborhoods. Reflecting these benefits, cities around the world have launched ambitious tree-planting campaigns, including Montreal, New York, Paris, and Shanghai. As part of its climate adaptation strategy, Montreal has committed to planting 500,000 new trees by 2030. But will half a million trees be enough to meaningfully cool the city? What kind of temperature reductions can residents realistically expect?
In this post, we’ll explore the science behind how trees cool cities, how their impact changes with scale (from a single block to an entire city), and some of the practical considerations Montreal will need to weigh, such as which neighborhoods have the most space for new trees. We’ll also do some back-of-the-envelope calculations to see whether Montreal’s tree-planting plans are likely to meaningfully cool summer temperatures across the city.
The Science Behind Tree Cooling
Trees help cool cities in three main ways. First, they change albedo, which is how much light is reflected from a surface. Compared to asphalt or concrete, leaves reflect more sunlight and therefore absorb less heat. Second, through evapotranspiration, trees draw water from the soil and release it into the air, cooling the surrounding environment as the water evaporates. This is much like how sweat cools your skin. Third, their canopies change how smooth the city surface is and alter the landscape, influencing wind flow and how heat moves through the air.
These cooling effects are strongest during the day, when trees are actively reflecting sunlight and performing photosynthesis, which drives evapotranspiration. At night, these processes stop, and trees can actually trap some longwave radiation near the ground. Due to this day-night cycle, a tree’s cooling effect follows a predictable pattern: it peaks in the afternoon and is more modest at night.
But not all trees or urban settings cool equally. The actual impact of tree cooling depends on a mix of factors, including tree traits, the layout of the city, and local climate conditions.
Urban Factors that Affect Cooling
Not all trees or urban environments cool the same way. A mix of deciduous and evergreen species in tropical, temperate, or continental climates can lower temperatures by about 0.5 °C more than planting a single type. Canopy density and height matter too: taller, fuller trees block more sunlight and release more moisture through transpiration. Even leaf traits, like size, thickness, and whether they stay year-round, change how effectively a tree shades and cools its surroundings.
Urban morphology also shapes cooling, with factors such as building morphology, road orientation, tree location and arrangement, and tree density playing important roles. Open areas with a variety of tree types see the strongest daytime temperature drops, with better air circulation and more shading. In contrast, compact neighborhoods require more strategic planting, since dense structures (including canopies) can trap heat.
Local climate is another key factor. In hot, dry regions, trees cool mainly through transpiration. In humid areas, this effect is weaker because evaporation slows in already moist air. For example, arid cities often gain the most from drought-tolerant evergreens.
How Canopy Scale Affects Cooling
Another important factor is the size of the area that trees cover. We’ve long known that trees can cool small neighborhoods, but the extent to which they can lower temperatures across entire cities is a trickier question.
Take Madison, Wisconsin, for example. In 2024, a study by Ziter et al., from the University of Wisconsin–Madison and Memorial University of Newfoundland, had volunteers bike around the city with temperature sensors. Their data showed that neighborhoods with more than 40% tree canopy were several degrees cooler than areas with sparse coverage. This is great news for the high-canopy neighborhoods, but clearly those isolated patches alone aren’t enough to cool the entire city. It’s also unclear what the maximum cooling potential would be if the entire city had a more evenly distributed canopy.
It’s long been known that cooling potential doesn’t scale linearly with increasing canopy cover, which poses a major challenge for urban planners trying to estimate how many trees are needed to make a difference at the scale of a city. In 2024, a study by Wang et al from the Chinese Academy of Sciences and the Cary Institute of Ecosystem Sciences showed that the relationship between canopy cover and cooling follows a power law. As canopy cover increases, so too does the cooling effect, but the rate of change is not linear; it plateaus as canopy cover increases past a certain point. The researchers developed an equation that lets cities estimate how much average temperatures could drop by expanding their tree canopy by 1%. This allows urban planners to set science-based canopy cover goals to fight extreme heat.
Deeper Dive: The Math Behind Tree Cooling
Researchers express the cooling effect of urban trees using cooling efficiency, which is the average temperature reduction caused by a 1% increase in urban tree canopy.
The summer daytimes formula looks like this:
Qs=kS𝛽
Qs = the expected cooling (°C) from a 1% increase in canopy
S = the size of the area being measured, in meters
k = a normalization constant
ß= a scaling exponent which quantifies the rate of scaling
The key insight: cooling efficiency grows with scale, but not in a straight line. Larger, connected tree patches provide disproportionately greater cooling than scattered ones.
What Does This Mean for Montreal’s Tree Planting Initiative?
So will the new tree planting campaign help cool Montreal? The answer is complicated and any estimate comes with big caveats. Still, we can get a rough sense using the power-law formula from Wang et al. 2024.
The island of Montreal covers about 472.6 km² or 472600 m². Plugging this into the study’s scaling equation, and using constants derived for the city with the most similar geographical location and climate (Baltimore) gives us:
Qs = 1.06(472600)0.066 = 2.51 °C
This means Montrealers could reasonably expect an average temperature reduction of ~2.5 °C on summer days if its urban tree canopy (UTC) increased by just 1%. Of course, this is a rough estimate - a more precise calculation would need to take into account Montreal’s unique climate, urban layout, tree composition, and other local factors.
How many trees would it take to increase canopy cover by 1%? The total number of trees in Montreal is difficult to quantify, but the city has been reported to host more than 1.2 million trees on public land alone. If we assume about half that number again on private land, a reasonable ballpark is around 2 million trees total. Increasing the UTC by 1% would mean planting roughly 20,000 new trees. Montreal has already committed to planting 500,000 trees, which is far more than what should be needed for a 1% increase in canopy cover, giving us good reason to be optimistic.
Making the Most of Montreal’s New Trees
To maximize the benefits of Montreal's tree planting initiative, the David Suzuki Foundation partnered with Habitat, a Montreal-based environmental solutions firm, to create a strategic, science-based tree-planting plan. Their goal was to ensure that this massive tree-planting effort delivers the greatest ecological, social, and climate impacts. The study uses both socio-economic and ecological indicators to guide decisions about where, how many, and what kinds of trees should be planted in Montreal. It also offers a roadmap that other municipalities could follow to meet climate and environmental equity challenges.
To start, the study examined the current status of Montreal’s urban forest. The city currently has 21% canopy cover, with L’Île-Bizard–Sainte-Geneviève at the high end (47.8%) and Saint-Léonard at the low end (9.7%). Functional diversity, which is a measure of trees’ ability to withstand stress factors such as drought, soil compaction, flooding, or unknown threats, was rated 5.9 out of 9, showing room for improvement to increase resilience.
Next, the study analyzed where new trees could physically be planted, taking into account factors like surface type (e.g., paved vs. grassy) and distance from existing trees. Neighborhoods with the greatest planting potential include Rivière-des-Prairies–Pointe-aux-Trembles (space for 134,639 new trees), Saint-Léonard (space for 35,756 new trees), and Montréal-Nord (space for 27,219 new trees). Areas with the least available space include Outremont (space for 3,916 new trees), L’Île-Bizard–Sainte-Geneviève (space for 27,040 new trees), and Pierrefonds-Roxboro (space for 40,584 new trees). Across the city, there is room for an additional 758,162 trees, which could raise canopy cover to 27.8%.
The study also prioritized neighborhoods to address social equity and climate resilience. Using indicators like the Canopy Index for green space equity, the Canadian Index of Multiple Deprivation for socio-economic equity, five Climate Hazard Vulnerability Indices (for heat waves, droughts, heavy rainfall, flooding, and storms), and the Tree Functional Diversity Index, the highest priority areas were identified: Rivière-des-Prairies–Pointe-aux-Trembles, Saint-Laurent, Mercier–Hochelaga-Maisonneuve, Villeray–Saint-Michel–Parc-Extension, and Ahuntsic–Cartierville.
Finally, the study examined which tree species are best suited to Montreal’s local environmental conditions to maintain ecosystem services over the long term. Currently, 34% of the city’s trees are maples. These trees excel at filtering air pollutants, capturing stormwater, and storing carbon, and they are highly resistant to heavy rainfall and flooding. However, they are vulnerable to drought and strong winds. By strategically planting species resilient to these threats while maintaining support for those already abundant, Montreal could more than double its functional diversity, strengthening the urban forest against pests, climate hazards, and other risks.
Conclusions and How You Can Help Grow Montreal’s Urban Forest
Montreal’s plan to plant 500,000 new trees by 2030 is an important step toward cooling the city and strengthening its climate resilience. Back-of-the-envelope calculations suggest that even a modest 1% increase in Montreal’s urban tree canopy (roughly estimated to be ~20,000 new trees) could lower temperatures by nearly 3°C. With the city’s ambitious tree-planting plans far exceeding that benchmark, the potential cooling benefits are even greater. And when this effort is combined with other strategies, such as increasing the number of green roofs, installing more reflective surfaces instead of heat-aborbant ones such as asphalt, and expanding public green spaces, the impact could be transformative for the city’s future.
It’s important to keep in mind that to maximize the ecological, social, and climate benefits of this initiative, we need to be strategic about where and how we plant trees. That means carefully selecting neighborhoods for planting, for example based on their planting potential and residents’ current access to green space, as well as choosing tree species that maximize functional biodiversity so that Montreal’s urban forest can withstand stresses such as pests and climate hazards like drought.
If you’d like to be a part of growing Montreal’s urban forest, there are plenty of ways to get involved. You can roll up your sleeves by volunteering with local tree-planting initiatives (e.g., Les amis de la montagne, Tree Canada), chip in with a donation, or simply help spread the word. Another option is advocating for more trees, green spaces, and urban forestry investments in your neighborhood (for a success story, read about the history of Falaise St-Jacques, which the city recently announced will be turned into a park). And if you have the space, planting a tree at home helps make a real difference. Thanks to programs like Un arbre pour mon quartier and Montreal’s Have a tree planted in honour of a life, it’s easier and more affordable than ever to add new trees on private property. With more than 60% of Montreal’s planting potential sitting in residents’ hands, every tree counts. Together, we can grow a cooler, greener, and more resilient city for generations to come.
Sources
Cities4Forests. Montreal. https://cities4forests.com/city/montreal/
Riga, Andy. Falaise St-Jacques: A pocket of wilderness in Montreal’s concrete jungle. February 4, 2016. https://www.montrealgazette.com/news/article257332.html
