Downtown Montreal is up to six degrees hotter than Mount Royal, study finds

Research led by a Montreal student shows that downtown can be up to six degrees hotter than greener parts of the city — a temperature gap with real consequences for health and equity as climate change intensifies.

Johanna Arnet is a master’s student at Université du Québec à Montréal (UQAM) and a member of its Chair on Urban Forests. Her research focuses on how spatial and temporal temperature patterns vary within the city, and how urban forests can help mitigate the effects of heat.

Using a bicycle with high-precision sensors — including air and surface temperature sensors, a pyranometer to measure solar radiation, and GPS — Arnet has been pedaling through different Montreal neighbourhoods to collect data at human height.

“We’re sampling every second, which means we’re gathering readings every few metres,” said Arnet, whose project is carried out in collaboration with both UQAM and Concordia University. “It’s very fine scale, and more relevant to human health than satellite imagery, which mostly captures surface temperatures on rooftops.”

Arnet said her routes were designed to capture differences in canopy cover and built environment, two major factors influencing local temperatures. One of her new routes, added this summer, goes from downtown Montreal to Mount-Royal Park.

“Along that stretch, we found an average difference of around six degrees, which is quite significant,” she said.

Temperatures are recorded between 3 p.m. and 5 p.m., typically the hottest hours of the day in the city. Additional measurements are also taken at night — at least three hours after sunset — when the urban heat island effect tends to peak.

Ville-Marie borough looking to make a difference

The study is being done in partnership with the Ville-Marie borough and the Quartier des spectacles neighbourhood, both of which are exploring ways to reduce heat through urban greening.

“There’s a whole bunch of tree-planting initiatives underway, and they were wondering which areas should be prioritized,” said Arnet. “This project helps map out the hotter and colder areas in the borough so that decisions can be more targeted.”

But cooling dense, downtown areas isn’t always simple. In the Quartier des spectacles, Arnet said, the layout changes constantly to accommodate various events such as festivals. Because of this, planting permanent trees isn’t always an option.

Instead, the neighbourhood has turned to a more flexible solution: mobile greenery.

“They have over 100 trees in pots that can be moved around to work within the changing layout,” said Arnet. “They even use some of them as road blockers to restrict car access, which is another innovative way to reduce heat without ripping up concrete.”

Arnet stressed the importance of mixing strategies — like adding shade structures, green roofs, or green walls — especially in areas where space is limited. The resilience of the city’s urban forest is also key, she added, noting the need for species diversity to protect against future pest outbreaks.

“Functional and structural diversity is crucial, trees, shrubs, and ground-level vegetation all play a role,” she said.

How heatwaves expose inequality

Isabella Richmond is a PhD student in biology at Concordia University researching how urban ecosystems and design can influence heat exposure and health outcomes.

“We define cities by their impervious surfaces, which basically means concrete, and in Montreal that’s definitely what comes to mind when you think of downtown,” said Richmond, who is helping with Arnet’s project.

With fewer trees and more built infrastructure, heat accumulates and radiates through the day and night. Richmond said that a six-degree difference is far from negligible.

“To the human body, that’s the difference between comfortable and dangerously hot,” she said. “Even a half-degree can be felt, so, six degrees is massive.”

She pointed to another example: the stark contrast between Park-Extension and the Town of Mount Royal. The two adjacent neighbourhoods show wide differences in canopy cover, housing density, and access to green space — and, as a result, temperature.

“There’s a real imbalance in who feels the worst of the heat,” said Richmond. “Urban design is everything.”

The consequences of heat exposure go beyond discomfort.

Richmond pointed to studies that have shown links between urban heat and higher risks of cardiovascular and respiratory illness. She noted that wealthier, whiter communities tend to live in cooler areas, a phenomenon she referred to as the “luxury effect.”

“And the people who live in hotter zones often don’t have access to things like air conditioning, either in their homes or even in a vehicle,” she said. “So not only are they experiencing higher temperatures, but they don’t have the same access to relief.”

As climate change accelerates, the research team hopes its data will help guide how and where cooling interventions are made and ensure they reach those who need them most.