Exploring Urban Sky Gardens’ Spatial Patterns, Influencing Factors and Optimizing Strategies in Lanzhou, China

Urban sky gardens—elevated green spaces on buildings, encompassing rooftop gardens and podium gardens—are critical to the improvement of urban ecosystem services and functions. Understanding the spatial patterns and the influencing factors of sky gardens is essential for the precise allocation of elevated spaces in urban development. Taking the four central urban districts of Lanzhou in China as the study region, a GIS database of 508 sky gardens was established by identifying high-definition image maps and on-site investigations. The spatial patterns and influencing factors, such as building height, ground-level green area, and population density, were analyzed. The development of sky gardens was also compared in Lanzhou and Guangzhou, China. The distribution of sky gardens in Lanzhou exhibited spatial heterogeneity. Most sky gardens were distributed along the Yellow River. Chengguan District had more sky gardens than Xigu District. In terms of structural characteristics, 82% of sky gardens were rooftop gardens, 73% were located in residential buildings, and 63% were attached to mid- and low-rise buildings. Most sky gardens were one floor, characterized by no public accessibility, a location in high-density plots, and low vegetation coverage. Sky garden area was negatively correlated with building height, ground-level green area, and green plot ratio in sky gardens. There were positive associations between sky garden area and higher plot ratio, building density, and population density based on Multiscale Geographically Weighted Regression. Due to the proper climate conditions and economy, Guangzhou had more sky gardens than Lanzhou. Our study suggests that the utilization of rooftops and podiums is relatively low, and the development of sky gardens exhibits spatial clustering. A suite of optimizing strategies should be implemented to enhance the accessibility and usability of sky gardens.