Assessing the relationship between urban structure and the urban heat island: Improving local climate zone mapping and estimating zonal and sub-zonal scale effects on air temperature

The urban heat island (UHI) effect is the phenomenon that the temperature in an urban area always higher than its surrounding rural area. The magnitude of UHI also varies substantially within the same city, causing unexpected extreme weather in summer, influence human thermal comfort, and hazard human health and local ecology. Local climate zone (LCZ) provides rich information about urban biophysical properties, strongly tracks the spatial variability of UHI. By using high-resolution 2D/3D data and object-based image analysis (OBIA), we generated an LCZ map with 81% overall accuracy. It shows a 17% improvement compared with the LCZ map with 64% overall accuracy by using a common process provided by the Database and Access Portal Tools (WUDAPT) process. In the zonal scale, the LCZ scheme effectively connects urban structures and air temperature by identifying temperature differences between LCZ categories, with daytime F-value = 824.5 and nighttime F-value = 268.3. The greatest inter-LCZ temperature variance is ∆TLCZA-LCZ2 =-3.78℃ at daytime and ∆TLCZA-LCZ2 =2.62℃ at nighttime. The intra-LCZ ∆T is usually 2~4℃. In the sub-zonal scale (10, 30, 60, 90, 120 m), daytime temperature decreases nonlinearly as the increase of pervious surface area and tree canopy. Nighttime temperature decreases nonlinearly as the increase of pervious surface area and linearly increase as the increase of the area of building surface. Research also shows the magnitude of urban heat island is strongly affected by valley terrain around Rock Creek Park and the meteorological conditions, which cannot be explained by the LCZ scheme.