Strategic green roof placement in Toronto to maximize benefits while incorporating citizen preferences

Abstract

Green roofs provide a broad range of ecosystem services, including air quality regulation, temperature regulation, flood regulation, and habitat provision. Through strategic placement they can address multiple urban challenges. However, city governments often do not engage in strategic spatial and fail to consider citizen preferences. To address this, we developed an approach for strategic placement of green roofs, based on the four mentioned ecosystem services for Toronto, Canada. We designed an approach based on biophysical information, which we further enriched with data on citizen preferences for different ecosystem services. We used literature-derived criteria and spatial analysis to identify optimal green roof placement locations for each ecosystem service separately, and the four services combined. A citizen survey was conducted (n = 402) to rank ecosystem services based on preferences. Mean rankings were used for a citizen-weighted model for strategic green roof placements. Our approach identified key priority areas for Toronto, while also highlighting that a significant portion of the city’s rooftops are sub-optimal for maximizing the benefits of all four ecosystem. However, by focusing on turning roofs in hotspot areas (0.2–1.2 % of total roof space) into green roofs, the four ecosystem services could be enhanced simultaneously. Results showed large spatial variations in priority areas between individual ecosystem services. However, comparing results across the biophysical and citizen weighted approach for all ecosystem services combined indicated similar priority areas, suggesting citizen support for prioritisation related to biophysical needs. Moreover, citizen involvement in governance practices can foster transparency, inclusivity, and satisfaction in strategic planning of green roofs. The methods employed in this study can be adapted to other cities worldwide, enabling more strategic, participatory approaches to implementing green roofs to enhance multiple ecosystem services where they are valued most.