Quantifying the cooling distance of green space by grid screening method: A case study of the Zijin Mountain in Nanjing

The cooling distance is one of the key metrics for assessing the cooling effect of urban green space (UGS). In this paper, a grid screening method (GSM) was proposed by screening the LST pixels around the target green space (TGS) to control the effect of other factors that affected the LST. Then the function of Normalized LST (NLST) and Normalized Distance (ND) was constructed using the selected pixels to obtain the cooling distance of TGS. Taking the Zijin Mountain in Nanjing as an example, after controlling the effects of adjacent UGS and the difference of underlying surface type, the LST was significantly positively correlated with the distance, and 24.8% - 63.8% of the data can be explained by the fitting result of the cubic function. The results showed that the Zijin Mountain's cooling distance ranged from 670 m to 1225 m, with an average of 819 m. Compared with the buffer method which is widely employed for UGS cooling distance, the results from the GSM had higher accuracy and stability. This paper aims to investigate a more reliable method which would enable researchers to characterize the cooling distance of UGS effectively.