"Green Alleys" Were Not a Panacea—The Key to Cooling Cities Lies in "For Whom They Are Made"

When it comes to urban heat countermeasures, large parks, street trees, rooftop greening, and green infrastructure that absorbs rainwater come to mind. However, in densely populated cities, there is no land available to create large new green spaces. This is where the concept of "green alleys," which involves greening narrow alleys behind residential areas, comes into focus.

A green alley is an initiative to redesign alleys, traditionally used for vehicle passage, garbage collection, and backdoor access, with plants, trees, permeable pavement, rain gardens, benches, playgrounds, and murals. It is expected not only to beautify the area but also to alleviate urban heat, increase habitats for living creatures, return rainwater to the ground, and foster interactions among residents.

However, a new study led by a research team at Concordia University in Canada raises an important question: Does greening alleys truly produce the expected effects? The answer is not simple. The study reveals the reality that the name "green alley" alone guarantees nothing. The effects depend on the purpose for which the alley is designed, by whom, how it is designed, and how long it is maintained.

The study compared two cities in Quebec, Canada: Montreal and Trois-Rivières. Both are working on green alleys, but their approaches differ significantly.

In Montreal, resident-led initiatives are prominent. In one alley, a children's playground was created; in another, murals were painted; and in yet another, concrete was removed to plant trees and flowers. Each area has its own character, and residents' wishes are easily reflected.

On the other hand, Trois-Rivières adopts a more standardized, government-led program. The main focus is on rainwater management, and ensuring that vehicles like garbage trucks can pass through is also prioritized. As a result, the arrangement of plants and the shape of the pavement are relatively consistent, with designs combining lawns and concrete driving lanes.

The research team surveyed a total of 53 green alleys, 23 traditional gray alleys, and 76 nearby street sections in Montreal's Villeray–Saint-Michel–Parc-Extension district and Trois-Rivières. The survey was conducted in the summer of 2023, recording tree species, vegetation layers, canopy cover, and the presence of native or non-native plants. In Montreal, the presence of fireflies was also tracked as an indicator of habitat.

Additionally, temperature sensors were installed to observe cooling effects, recording air temperature every 15 minutes over several weeks. The research team also interviewed 30 residents, walking through the neighborhoods to investigate elements that residents value, such as shade, greenery, and visual comfort.

The results were intriguing. Standardized, government-led alleys like those in Trois-Rivières showed more consistent environmental effects, particularly in lowering nighttime temperatures. However, their design did not necessarily meet residents' desires. For example, even if residents wanted more and larger trees, vehicle passage and management convenience were sometimes prioritized.

In contrast, Montreal's resident-led approach easily creates social appeal and local character. Alleys become places for children to play, and murals and benches contribute to community identity. When residents are highly engaged, alleys become more than just pathways; they become semi-public gardens or small plazas.

However, this high degree of freedom also leads to variability in effects. The study found that while some green alleys in Montreal had more trees than their surroundings, the trees were small and did not provide sufficient shade or cooling effects. In some places, there was less canopy cover than nearby regular streets, and temperature data showed modest and highly variable cooling effects. Some green alleys performed the same or worse than traditional gray alleys at certain times.

In other words, it cannot be simply said that green alleys are "cool because they are green." Small plants and lawns alone cannot provide enough shade. Young trees may have an impact in the future, but they do not significantly reduce urban heat immediately after planting. Cooling effects are determined by a combination of alley width, building shadows, paving materials, ventilation, soil, moisture, tree size, and arrangement.

This study is particularly important because it highlights the multiple objectives embedded in the term "urban greening." For some municipalities, the goal may be to increase canopy cover. For others, it may be to absorb rainwater into the ground instead of letting it flow into the sewer system. For residents, it may be a place where children can play safely, a pleasant path for walking dogs, an opportunity to meet neighbors, or simply a comforting view when returning home.

Different objectives lead to different designs. If rainwater management is the top priority, permeable pavement, rain gardens, and drainage flow become important. If heat countermeasures are prioritized, selecting and arranging trees that provide ample shade once grown is essential. To enhance biodiversity, it is necessary to consider native plants, multi-layered vegetation, pesticide-free management, and habitats for small animals and insects. If resident interaction is emphasized, creating spaces that are easy to use for sitting, visibility, safety, and accessibility for children and the elderly is necessary.

Conversely, a "green alley that maximizes all effects simultaneously" does not easily exist. If paving is widened for vehicle access, planting areas decrease. If a large playground is created, dense vegetation that serves as a habitat for creatures may be limited. Increasing large trees may cool the area but also increase the burden of fallen leaves, roots, and maintenance. Increasing resident freedom fosters attachment, but it can lead to differences in quality and long-term management among alleys.

Reactions on social media also reflect this complexity.

Reactions to the article itself, as far as can be confirmed, are not widespread but are shared among researchers, university affiliates, and those interested in urban planning and environmental fields. On LinkedIn, there is a post introducing the article, emphasizing that green alleys are not a plug-and-play solution for urban sustainability, highlighting the importance of design objectives and ongoing support. On X, Concordia University's news account introduces the research findings, stating that while green alleys can enhance biodiversity and social connections, there is no universal design.

On the other hand, on Reddit, there is a long-standing accumulation of reactions to Montreal's green alleys. In one post, a photo project visiting numerous green alleys in Montreal received a brief compliment, "Very cool." In another urban photography post, snowy back alleys in Montreal received reactions like "should be more appreciated" and "really love it." Green alleys and alley spaces are perceived not just as infrastructure but as landscapes that shape the atmosphere and memory of the city.

However, not all reactions are positive. A Reddit post in Montreal sparked discussion about residents blocking the entrance to a green alley with a homemade barrier and "private property" signs. Questions arose about whether it was a public space or private property, what the right of way was, and what the designation of a green alley meant. Another comment pointed out that while green alleys can be beautiful and comfortable, if residents do not continue to maintain them, they can become more like a "jungle" than a "park."

This temperature difference on social media closely aligns with the research results. People find green alleys attractive. They are photogenic, enjoyable to walk through, and places to be proud of if they are in the neighborhood. However, behind this lies the realistic issues of who will manage them, who will bear the costs, how to deal with vehicles and garbage collection, and how to delineate public and private use.

The research also points out that older green alleys tend to lose greenery due to a lack of maintenance funds. Even if there is enthusiasm at the time of initial development, continuous effort and funding are required for watering, pruning, replanting, cleaning, and repairs. If the burden is shifted to individual residents, the project may weaken due to aging residents, relocations, declining interest, and economic disparities.

This is a common challenge for urban greening in general. Green infrastructure is not complete at the moment of completion. Rather, its value is determined over 10 or 20 years after installation. Trees take time to grow. Plant communities can become rich or barren depending on management. Resident relationships are maintained only with continuous participation.

So, how should cities design green alleys?

The study suggests the need to combine government-led and resident-led approaches, rather than choosing between the two. Standardization by the government alone makes it easier to achieve measurable outcomes like rainwater management and canopy goals. However, it does not necessarily create spaces that are truly user-friendly for residents. Conversely, leaving it entirely to residents may foster local character and attachment but makes it difficult to stabilize environmental performance like cooling effects and biodiversity.

The ideal approach would be to start with the uses residents desire, supported by expert design, and guaranteed long-term funding and maintenance by the municipality. For example, if residents want a place for children to play, safety and visibility should be ensured while incorporating trees that provide shade and plantings that absorb rainwater. If residents want a cool pathway, it is not enough to simply place flower beds; tree species and arrangements should be determined with future canopy formation in mind. To aim for biodiversity, consider combinations of native plants that are easy for insects and birds to use, not just neatly arranged flower beds.

Furthermore, the indicators for evaluating the effects of green alleys should not be singular. Looking only at how much the temperature has dropped overlooks resident satisfaction and interaction effects. Conversely, looking only at popularity with residents may overestimate contributions to urban heat countermeasures and rainwater management. It is necessary to comprehensively consider temperature, canopy, rainwater infiltration, biodiversity, usage frequency, resident satisfaction, and management costs.

This topic is not unrelated to Japanese cities. In Japanese residential areas, there are many narrow alleys, back streets, private roads, living roads, parking lot gaps, and spaces behind buildings. Urban heat is becoming increasingly severe, and the drainage load from guerrilla rainstorms is also a problem. In areas where it is difficult to establish large parks, how to utilize small spaces is becoming increasingly important.

However, if similar initiatives are to be pursued in Japan, it is necessary to carefully organize rights relations, fire and evacuation routes, garbage collection, neighborhood troubles, and maintenance responsibilities. Alleys, being close to home, directly impact residents' lives. Even a single potted plant can become an obstacle to passage. Beautiful greening can become a concern for insects, fallen leaves, humidity, and security for some people.

Therefore, the essence of green alleys is not "placing greenery." It is a design issue of how to layer environmental and living functions in small urban spaces. And this design does not end with blueprints. It questions whether users, managers, passersby, the government, and experts can share the same purpose.

This study does not deny the expectations for urban greening. Rather, it can be seen as a warning to realistically draw out the potential of green alleys. Alleys are precious spaces left in cities. Planting trees, blooming flowers, and creating places for people to stop have great significance. However, to truly connect these effects to urban heat countermeasures, biodiversity, and residents' livability, the label "greened" is not enough.

What is needed is to clarify the purpose, align design with that purpose, listen to residents' voices, incorporate expert knowledge, and create a system that supports it long after development.

Green alleys are not a magical solution to transform cities. However, if well-designed and carefully nurtured, they can become small gateways for people and nature to meet once again in a city covered in concrete.

Source URL

Phys.org. Refer to the overview of the Concordia University-led study, research subjects, comparison of Montreal and Trois-Rivières, and challenges of cooling effects and maintenance.
https://phys.org/news/2026-04-green-alley-effectiveness-purpose.html

Official Concordia University news article. Refer to the background of the study, researcher comments, research methods, and differences in design philosophy between cities.
https://www.concordia.ca/news/stories/2026/04/28/green-alley-effectiveness-depends-on-design-and-purpose-concordia-led-study-finds.html

Research paper "Green alleys in Quebec provide variable biodiversity support and ecosystem services." Refer to the original study.
https://www.tandfonline.com/doi/full/10.1080/26395916.2026.2624451

LinkedIn post. As an example of social media sharing of the article, refer to the reaction emphasizing that green alleys are not a simple solution for urban sustainability and the importance of design and ongoing support.
https://www.linkedin.com/posts/patricklejtenyi_green-alley-effectiveness-depends-on-design-activity-7454919749399961601-HYCI

X's Concordia University news account. Refer to the example of social media dissemination of the research introduction.
https://x.com/ConcordiaUnews

Reddit urban planning community post. Refer to an example of a favorable reaction to Montreal's green alleys.
https://www.reddit.com/r/urbanplanning/comments/iejnw5/there_are_443_green_alleys_in_montreal_canada_i/

Reddit Montreal community post. Refer to reactions concerning the public nature, management, and resident disputes of green alleys.
https://www.reddit.com/r/montreal/comments/1od7t5g/voisin_qui_sapproprie_une_ruelle_verte/

Reddit urban photography community post. Refer to an example of a favorable reaction to the alley scenery in Montreal.
https://www.reddit.com/r/CityPorn/comments/ep2acy/a_montreal_backalley_bonussnow/