The development of urban sky gardens in the river valley city of Lanzhou, China.

Background and aims: Urban sky garden is critical to the improvement of human well-being and health, the distribution, area and accessibility of urban sky garden has received widespread concern. Understanding the distribution characteristics and influencing factors of green roofs is of great significance for the precise allocation of vertical space in the stock development phase. Methods: Taking the four central urban districts of Lanzhou as study region, a GIS database of 508 rooftop gardens was established by identifying high-definition image maps and on-site investigations. The distribution characteristics and influencing factors were analyzed from different aspects such as building height, ground greenery area, population density, building density and plot ratio, etc.Key Results: The distribution of sky garden in Lanzhou has spatial heterogeneity. Most sky gardens are distributed along the Yellow River. Old towns have higher sky gardens than new towns. 61% of sky gardens were located in Chengguan District, 82% were roof gardens, 73% were residential buildings and most were low buildings. 98% of sky gardens were one floor and 97% were non-open. 96% were in high density plot and had low green plot ratio. Urban sky garden areas were negatively correlated with building height, building storey, ground greenery area, ground greenery ratio and green plot ratio in sky gardens.Conclusions: Our study suggests that sky gardens serve as a complement to ground green spaces in Lanzhou. However, the utilization rate of rooftops is relatively low, and the sky garden development of different types of buildings is not balanced. Future research on the enhancement of urban green spaces urgently needs to shift from two-dimensional to three-dimensional approaches and integrate vertical space. This is especially important for enhancing the accessibility, equity and diversity of rooftop gardens.