Development potential of sky gardens in the compact city of Hong Kong

Sky gardens have been actively studied and installed in different cities. Their development potential in compact developing cities has received little attention. Using remote sensing and GIS techniques, this study evaluates the vegetation configuration and development potential of sky gardens in urban Hong Kong, their underlying location, land use and building factors, and future planning and implementation concerns. Existing sky garden area is limited with sparse vegetation cover and low biomass. Existing podium gardens exceed roof gardens by about nine times. District development age has little effect on existing and potential sky gardens. Old towns have higher potential roof and podium gardens than new towns in most land uses. The effect of land use on potential sky gardens varies greatly by districts. Buildings with 10–20 floors have higher potential roof gardens in most districts. Building area is the main determinant of potential roof garden, and population density of potential podium gardens. Three scenarios of realization, namely minimum (20%), medium (50%) and maximum (80%), are adopted to project sky garden provision in individual districts. The projection extends to the contribution of new sky gardens to urban greening in terms of green cover and greening rate in districts. The challenges include susceptibility to typhoon damage in high-rise exposed sites, aggressive weed invasion, lack of roof-slab loading data in old buildings, and poor building maintenance. The opportunities include affordability of the new technology, enabling government policy, and establishment of scientific and research foundation in the local context. The development strategy could aim squarely at stringent technical standards and contractor skill requirement, and programme prioritization based on research findings. The study provides useful hints, approaches and recommendations for a systematic sky-garden action plan in Hong Kong and other similar compact cities.