Remote sensing for healthy vegetation on green roofs

Green roofs have been increasingly implemented in cities globally to enhance urban ecosystem services. However, temporal trends in green roof vegetation health and the effects of design considerations at a large scale remain unclear. Here we used very high-resolution multispectral remote sensing imagery to quantify the temporal changes in vegetation health and associated roof characteristics across 1,380 individual green roof units in Toronto from 2011 to 2018. Results show an average increase in vegetation health and a decline in vegetation patchiness as green roofs age. We identify unit area, building height and vegetation type as the primary roof characteristics influencing vegetation health, with area positively and building height inversely affecting vegetation health. In terms of vegetation type, sedum mats are generally healthier than woody plants and grasses. Additionally, we identify critical thresholds in roof characteristics that support sustained vegetation health. These findings present a robust analytical framework for the long-term assessment and design optimization of green roofs in complex urban environments.