A research team from the John H. Daniels Faculty of Architecture, Landscape, and Design at the University of Toronto conducted a systematic ecological analysis of nearly 1,500 green roofs across Toronto using aerial remote sensing technology. The study, published in the journal Nature Cities, provides a scientific framework for the future planning and design of urban green roofs.
The team analyzed high-resolution aerial imagery collected between 2011 and 2018, using multispectral data to track long-term changes in green roof vegetation. The data show that as green roofs age, the health of vegetation on most roofs tends to improve, with vegetation distribution patterns becoming more concentrated. University of Toronto Professor Sean C. Thomas stated: "Being able to track the development of green roofs over the long term gives us real insight and guidance on how to do green roofs better."
The study also found that building structure significantly influences green roof performance. Vegetation on rooftops of high-rise buildings generally grows more poorly than on buildings of four stories or fewer, and long, narrow roof designs are more prone to vegetation degradation. Currently, most green roofs use drought-tolerant plants from the Sedum genus, which employ a special mechanism of storing carbon dioxide at night and performing photosynthesis during the day, effectively adapting to the shallow soil environment of rooftops.
Thomas noted: "Traditional flat or sloped roofs drain rapidly during extreme rainfall, overwhelming infrastructure. Green roofs are an effective way to store water and delay flood peaks." These green roof systems not only mitigate the urban heat island effect but also reduce noise pollution, improve air quality, and enhance urban biodiversity by supporting habitats for insects and birds.
In 2009, Toronto became the first city in North America to implement mandatory green roof regulations. This research will serve as an important reference for future green roof design and help elevate the level of sustainable urban development.
