Effects of Area and Shape of Greenspace on Urban Cooling in Nanjing, China

Urban greenspaces play a key role in mitigating the urban heat-island (UHI) effect. The aim of this study is to quantify the effects of area and shape of a greenspace on urban cooling using correlation analyses and regression models. This was achieved by taking a very densely populated urban area in Nanjing, China, as a case study and classifying 78 greenspaces within the study area into nine groups based on size and shape. Cooling distance and intensity values were calculated based on the land surface temperature derived using remote sensing. The results indicate that (1) large and regular greenspaces have a greater cooling distance than small and irregular ones; (2) in general, an increase of area can enhance the cooling intensity of a greenspace when it is smaller than a certain threshold (i.e., 10 ha); and (3) reducing the shape complexity of a greenspace can enhance cooling intensity when greenspaces are larger than 5 ha. This study provides insights for urban planners and landscape designers to determine better combinations of area and shape of urban greenspace in order to effectively alleviate the UHI effect.