Considering local contexts in downscaling national SSP narratives to municipal and district scales for future urban microclimate simulations

Projecting future urban forms is a crucial step in assessing the local impacts of climate change at municipal or district scales. Since O’Neil et al. (2017) developed the global SSPs framework, several studies have downscaled it to construct localized scenarios for nations and regions. However, future land use and building stock referenced in urban climate studies are often provisional and do not adequately reflect region-specific conditions and policies. Therefore, this study downscaled national SSP narratives by considering local contexts and projected future land use changes at the municipal scale and building stock changes at the district scale. The target municipality was Nagoya City, the central city of the third largest metropolitan region in Japan. The projections were conducted for SSP1 (Sustainability) and SSP5 (Fossil-fueled Development), based on expert judgment by members including urban planning experts. First, to project land use, we divided the entire municipal area into several zones expected to undergo similar changes and determined the rate of future change for each zone. As a result, under SSP1, the projection reflected changes in the concentration of residential building sites around railway stations, as Nagoya City is officially envisioning the “compact plus network” urban structure. Second, to project building stocks changes in a certain district, we determined the timing and policies for building reconstructions at each site based on factors such as the age of existing buildings. As a result, under SSP1, the projection reflected the trend that old buildings will be demolished due to the population decline, and the sites will remain as open spaces for multi-purposes. Finally, we conducted a future microclimate simulation for the district, demonstrating the practical application of the outcomes of this study. We hope that these outcomes will contribute to the collaboration between climate science and urban science.