Study on the Scale Effect of the Cold/Heat Islands Pattern in Nanjing

Changes in urban land cover types affect the spatial pattern of urban thermal environments, and the relationship between urban land cover types and urban cold/heat island patterns is of great significance for regulating urban microclimate, improving human settlements and improving urban resilience. Based on the landsat8 Satellite imaging data, the parameters of the four main types of land cover (water, vegetation, impervious surface, building) in Nanjing were extracted, at the same time, the surface temperature was retrieved using the thermal infrared band. The relationship between the spatial distribution of cold/heat islands and the main land cover types was studied from two scales: pixel (small) and city and district administrative division (middle) , and the scale effect was discussed in depth. The results are as follows: The spatial analysis based on the pixel scale shows that the distribution of vegetation and water is related to the spatial pattern of cold islands; the order of cooling effects of different types of surface types is: water＞vegetation＞impervious surface＞building; the distribution of buildings and impervious surfaces is related to the spatial pattern of the heat island. The spatial analysis based on the scale of administrative divisions of cities and counties shows that the four types of land cover have a lower correlation with the cold island effect; buildings and impervious surfaces are highly correlated with heat island effects, and in particular, buildings and heat island effects have the highest correlation (R²=0.95). In general, research based on small scale can reflect the correlation between surface cover types and spatial distribution of cold/heat islands, while research based on mesoscale reflects the comprehensive characteristics of urban thermal environment from a statistical perspective. The research can help urban planners understand the scale characteristics of urban cold/heat island formation, and provide a reference for coping with global climate change, rationally planning urban layout, and promoting sustainable urban development.