Utilization of roofs in Sumida Ward, Tokyo: Analysis of the potential CO2 emission reductions and other co-benefits

CET Lunches will be virtual until further notice.

Cities occupy only a small fraction of global land, between 0.2% to 2.7% (Schneider et al., 2009; IPCC, 2014), but they consume approximately 70% of primary energy and account for about the same percentage of GHG emissions globally (Svirejeva-Hopkins et al., 2006). Currently, more than half of the world's population resides in urban areas, and the urban population is expected to increase from the current 52% to roughly 70% by the middle of this century (Kolokotroni et al, 2016).

Such continued urbanization has numerous negative environmental and ecological impacts. Urban green spaces, and broader green infrastructure, provide multiple benefits that enhance urban livability and sustainability, ranging from the mitigation of air pollution, urban heat island (UHI) effect and other environmental benefits, to multi-dimensional benefits to human wellbeing. However, urban green space expansion is not always feasible in many cities. Interventions within the urban landscape can help in mitigating this increase of GHG emissions as well as other environmental problems, however due to the locked in infrastructure, changing the urban structure or adding new elements is often not feasible.

Roofs account for between 20 – 30% of urban surface space and most of it is unused (Akbari et al., 2009; Byrne et al., 2015). In these contexts, there have been proposals to utilize rooftops as green roofs to gain some of these benefits. This study spatially identifies areas where roofs have the potential to provide different types of benefits associated with urban green spaces if they are retrofitted with green roofs. Through a GIS-based approach we catalogue available roof space in Sumida ward in Tokyo for green roof implementation and evaluate each roof patch’s potential to offer benefits if retrofitted with a green roof.

About the speaker

Jelena Aleksejeva is a PhD candidate in the Graduate Program in Sustainability Science - Global Leadership Initiative, The University of Tokyo. Between 2018 - 2021 she was a Research Assistant at the Center for Global Environmental Research of the National Institute for Environmental Studies (NIES), Japan. Jelena holds an MSc in Environmental Sciences from the University of Tsukuba, with certificates from the Environmental Diplomatic Leader program (EDL) and the International Collaborative Environmental Program (ICEP). Her broad research interests are in climate change mitigation and adaptation strategies in urban settings, smart cities, and green technologies, including green roofs.