Multiscale rooftop greening and its socioeconomic implications in Hong Kong

Rooftop greening stands as a distinctive approach to delivering green space without occupying ground-level areas. The spatial configuration of rooftop greenery and its socioeconomic associations are critical for sustainable urban development and environmental justice. However, historical research trends have predominantly concentrated on open, ground-level environments, neglecting the vertical manifestation of urban greenery. Investigations into green roofs have typically been circumscribed to their environmental benefits, while little attention has been paid to the spatial distribution of rooftop greenery and the drivers behind it. This study aims to fill the gap by implementing a multiscale mapping approach with satellite imagery to quantify rooftop greenness in Hong Kong. An integrated analysis incorporating geographic and demographic data reveals a correlation between rooftop greenness and factors such as income levels, housing types, residential area sizes, and household compositions. This association exhibits pronounced environmental inequality, where lowerincome individuals, solitary residents, and households with smaller living spaces in densely populated and aged neighborhoods are deprived of rooftop green spaces, in contrast to their counterparts in more affluent neighborhoods. Government-subsidized public housing initiatives have significantly contributed to enhancing the green living environment for low-income families. Buildings administered by government have demonstrated exceptional performance in rooftop greening efforts. This evidence provides nuanced insights into the advantages and deficiencies of green roof planning in Hong Kong and could serve as a critical reference for other densely urbanized cities working towards a sustainable and equitable urban green environment.