Mapping Vancouver’s Green Infrastructure and Roofscape with Gentian
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Introduction
In early 2024, the Green Roof Infrastructure Network (GRIN) launched a ground-breaking project to map climate action through green roofs, trees and green spaces for communities across British Columbia (BC). This article shares the first round of results and reflects on how this UK-based technology can help towns and cities across North America strategically establish resilience to flooding, drought and urban heat, while protecting biodiversity.
The Green Roof Infrastructure Network (GRIN) of British Columbia (BC) was established in 2023 as a response to the discontinuation of green roof programming at the British Columbia Institute of Technology (BCIT), and to promote green roofs and green infrastructure in BC. One of GRIN’s purposes is to guide and support BC municipalities in developing and promoting proactive policies that enhance biodiversity, reduce stormwater runoff, mitigate urban heat and improve liveability through urban greenery.
As such, GRIN decided to create a baseline map to assess the green infrastructure of BC towns and cities, with emphasis on green roofs (existing and potential), private gardens and urban trees. What is unique about the project is the innovative tool being implemented. GRIN is collaborating with Gentian Ltd and Dusty Gedge, who many green roof practitioners know from his effective work for green roofs and biodiversity in the UK and Europe. His passion and expertise contributed to London’s green policy (2016).
Fun fact: Gentian was co-founded by Dusty Gedge, as a result of his manual mapping of green roofs and potential retrofits in London’s boroughs. The company emerged from a meeting of minds to enhance Dusty’s know-how with artificial intelligence, computer vision, and high-resolution remote sensing to conduct rapid ecological surveys. Established in 2020 with funding from the European Space Agency, Gentian’s goal is to reverse biodiversity loss.
The mapping technology was well-timed for programs like Biodiversity Net Gain and Task Force on Nature-Related Financial Disclosures, given its ability to:
Demonstrate connectivity opportunities for wildlife
Clarify the type and quality of habitat available within urban limits
Assess potential green roof retrofits for existing buildings
Identify strategic investments in green infrastructure (especially for areas prone to flooding, urban heat, etc.)
Illustrate the benefits that green roofs provide at scale
The project with GRIN is Gentian’s first mapping of a North American city. It is framed as a fundraiser, in partnership with the Small Change Fund, which means that more donations will enable GRIN to map – and empower – more BC communities. A generous initial donation enabled the analysis of a 20 km2 Area of Interest (AOI) in the City of Vancouver. Donations of $10 or more through the Small Change Fund will receive tax receipts in Canada. This creative and collaborative fee structure means that municipalities can access the data at scale, while building owners can pay in to understand their specific impacts and offset the costs. Gentian's pricing for their Urban Green Infrastructure Mapping service is calculated based on variables such as the areas being mapped and the number of applicable reports wanted or required. Pricing for Urban mapping projects is therefore on a case-by-case basis.
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Fig. 1. The trained algorithms can quickly ascertain and distinguish different types of urban vegetation, including green roof types.
The Project: Mapping BC Communities for Existing and Potential Green Infrastructure
Fig. 2. Of 283 green roofs in downtown Vancouver, 83.8% were extensive (green dots) and 16.2% were intensive systems (turquoise dots).
The Vancouver mapping project used very high resolution satellite imagery (30-50 cm) from summer 2023 to locate and analyse green roofs and other forms of vegetation within the 20 km2 Area of Interest (AOI). Buildings and private garden borders were determined using data from OpenStreetMap and British Columbia ParcelMap, after which Gentian's AI models were applied to the imagery within these borders. The output generated a detailed analysis of green roofs, private gardens and trees. Figure 1 shows the analysis of two buildings, one with extensive green roofs and one with an intensive system.
As shown in Figure 2, only 283 of the 9,526 buildings mapped in the 20 km2 AOI had green roofs, of which 83.8 percent were extensive and 16.2 percent were intensive systems. The analysis does not include roofs with planters that are impermanent and not integrated into the roof structure. The 283 green roofs identified cover nearly 100,000 m2, or just under 2 percent of the otherwise impervious roofscape.
Since the most sustainable building is one that already exists, the study also analysed green roof retrofit opportunities in the AOI. Retrofits were identified as inverted roofs (i.e., shingle and paved roof surfaces) (shown as white dots in Figure 3) and multi-storey car parks (brown dots) with a load-bearing capacity of at least 120 kg/m². Given that the estimate is based on a remote assessment, and restricted to inverted roofs only, these results are conservative meaning more retrofits are likely.
Fig. 3. Numerous green roof retrofit opportunities exist in downtown Vancouver.
The economic significance of the retrofit analysis cannot be understated. Given their construction was already engineer-approved for 120 kg/m², verifying these roofs for a retrofit by a structural engineer will be straightforward and, therefore, economical. Obviously retrofits also need to consider other factors, such as roof access.
Discussion
This preliminary analysis shows that green roofs in the 20 km2 AOI cover minimal surface area, which is remarkable given that this area is home to numerous renowned projects (e.g., Vancouver Public Library, Vancouver Convention Centre, Robson Square, Olympic Village, Vancouver House). Green roofs cover less than 2 percent of the impervious roofscape, which means that green roof co-benefits here are restricted to building scale (e.g. cost savings for residents on air conditioning, cost savings for building owners on re-roofing). The wider benefits, like urban cooling and stormwater mitigation, can only be delivered when green roofs are implemented at scale.
The maps also illustrate the effectiveness of policy levers, the case in point being Vancouver Olympic Village in south-east False Creek. That area is easily spotted in the maps because of the dense cover of green roofs, as well as street trees, bioswales and meadows, which were part and parcel with the LEED Platinum goals of that development. An overlay of these maps with heat and acoustic maps would likely reveal that the Olympic Village is cooler and quieter than neighbouring communities.
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Unlike the UK, Canada and the United States lack incentives or metrics to enhance habitat for biodiversity, so the granularity of this particular value is missing. Even so, the algorithms can distinguish between different green roof types (e.g., extensive green roofs based by simple Sedum or more complex meadow vegetation).
For the next phase of mapping, GRIN is considering whether to analyse the rest of Vancouver or elsewhere in the province. Given our recent work on how green roofs and green infrastructure can protect fire-prone communities, we are considering mapping a semi-arid community in the Okanagan. By creating a baseline map of existing and potential green infrastructure, communities can make informed decisions about natural asset management, which will influence liveability and resilience in the years ahead.
How To Get Involved
Now that the model is trained on a North American city, Gentian is ready to apply this service to other towns and cities across Turtle Island (North America). Please share this project with your networks and help grow this project. Contact GRIN about how this technology might work in your city.
Please make a donation to give this work a solid foundation to grow. Contributions of $10 CDN or more will receive a tax receipt for Canada. While the surveys are quick and cost-effective, funding is required to pay for:
proprietary satellite imagery
engineers to train the machine learning
generating and interpreting the data
translating data into action: ensuring the results get to the right people in the right places (municipal planners and other stakeholders).
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Dr. Christine Thuring is an inter-sectional ecologist who is passionate about biodiversity and healthy communities. She has worked with green roofs since 2001 via installation, design, maintenance, advocacy, education and research. Christine is the principal of Ecotone: Restoring Biodiversity and co-founder and Executive Director of the Green Roof Infrastructure Network (GRIN) of BC.
Dusty Gedge is a life-long naturalist and bird-watcher based in London. He founded Livingroofs.org, co-founded the Green Infrastructure Consultancy Ltd., and is a recognised authority, designer and consultant on green roofs and green infrastructure. Dusty is the former president and current Ambassador of the European Federation of Green Roof Associations (EFB).
