Building level heat-health risk assessment in a three-dimensional and deprived built environment in Hong Kong

Extreme heat events are becoming more frequent, intense, and prolonged under global climate change, with urban areas particularly affected by the urban heat island effect. Rapid urbanisation has transformed city environments through three interrelated features—high-rise morphology, dense building clusters with overcrowded housing, and socioeconomic disparities—compounding heat-health risks. While previous studies have examined these factors individually, few have assessed their combined influence at the building level. This study developed a heat-health risk index for a deprived Hong Kong neighbourhood, integrating hazard, exposure, and vulnerability. Heat hazard was estimated using complete urban surface temperature (CST), the aggregated thermal load across all building surfaces, capturing three-dimensional heat exchange in dense urban environments, derived from Landsat 8 imagery; while the latter two domains were derived from local data from the District Office and population census. Among 1277 buildings analyzed, the heat health risk index ranged from 0.163 to 0.661 during the day and 0.152 to 0.845 at night, with the highest risk concentrated in urban cores where overcrowdedness exceeded 400% and >25% of households were low-income. Our findings enable targeted adaptation measures such as prioritising cooling access and outreach for high-risk buildings, supporting resilience planning in high-density cities.