Impact of refined 2D/3D urban morphology on hourly air temperature across different spatial scales in a snow climate city

Urban morphology profoundly affects the air temperature, and a better understanding of their relationships is crucial for improving outdoor comfort and urban planning. However, how their complicated associations change across different times and spaces is not clear. This study compared the influence of the refined urban 2D/3D morphology on hourly air temperature in a snow climate city by using high spatial resolution GF-2 images, correlation analysis and multiple regression models at different spatial scales. Results indicated that: (1) the air temperature differences among the sites were much larger during nighttime (4.14 degrees C) as compared to daytime (2.22 degrees C). The spatial pattern of the hourly air temperature had similar distributions except at the hottest time of day. (2) The relationships between air temperature and urban morphology had an obvious spatial-temporal dependency. Overall, their connections became stronger as the spatial scale increased and tended to become stale at the 500 m scale; the effect of urban characteristics on average nighttime, lowest, and daily air temperature was larger than daytime air temperature, and there was almost no correlation between the highest air temperature and urban morphology. (3) The effects of 2D and 3D urban morphology on air temperature vary depending on the selection of spatial scales and the choice of different indicator of air temperature. Typically, the building height and volume had the strongest warming effect. The 3D metrics performed better in predicting air temperature than 2D metrics at the 500 m scale, while the influence of 2D features was stronger at the 1000 m scale. Regardless of the spatial analysis scale, 3D features had stronger correlations with average daily, daytime, and nighttime air temperature. Based on our results, 3D urban morphology indications, such as building height and volume, should be emphasized at the 500 m scale for urban planning. Arranging buildings and vegetation in a reasonable way could generate a better thermal comfort environment for city dwellers.