Relationship between land use variations and spatiotemporal changes in amounts of thermal infrared energy emitted from urban surfaces in downtown Tokyo on hot summer days

• Airborne TIR measurements with 2 m spatial resolution on hot summer days
• Spatial and temporal changes in amounts of TIR energy in downtown Tokyo at midday
• Large amounts of TIR energy in high density wooden residential areas
• Smaller amounts of TIR energy in areas with office and commercial buildings
• Decreases in TIR energy in urban renewal areas caused by incentive-based policies

This study investigated spatial and temporal changes in amounts of thermal infrared (TIR) energy emitted from urban surfaces in downtown Tokyo, using 2 m spatial resolution data obtained from airborne TIR measurements at midday on the three different hot summer days: August 7, 2007, August 19, 2013, and August 19, 2014. Detailed land use data were also used for analyses of relationship between amounts of TIR energy and land use variations. The results showed significantly large amounts of TIR energy in high density wooden residential areas, whereas amounts of TIR energy in areas with office and commercial buildings were relatively small. As for the areas with office and commercial buildings, we found that amounts of TIR energy in many parts of urban renewal areas had clearly decreased between 2007 and 2013. In the renewal areas, many green surfaces have been provided in public open spaces. This would be one of the main causes of the decreases in amounts of TIR energy. Creation of public open spaces has been promoted by an incentive-based policy that offers an increase in the floor area ratio as a reward for constructing public spaces. These results strongly indicate that some governmental measures like the incentive system enacted for the areas with office and commercial buildings are required to reduce radiant heat in the high density wooden residential areas, because the maximum occurrence frequency of heat strokes tends to be recorded in residential areas and at midday.