Previous studies of the effects of regional climate conditions on urban heat islands (UHIs) focused mostly on surface UHIs, whereas few considered canopy layer UHIs. In the present study, a numerical modeling method is used to investigate the impacts of regional climate conditions on canopy layer UHIs at the district scale while controlling for the urban morphology. The urban morphology is classified according to the local climate zone (LCZ) system as LCZ1-LCZ6. Analysis of the spatial distribution of the urban heat island intensity (UHII) show that the nighttime and daytime UHII are most significantly correlated with the air temperature and wind speed, respectively. In five typical cities, LCZ1 has the most obvious urban heat island (UHI) effect, with an average annual UHII of 1-2.3 °C, which is about 1.5 times that for LCZ4. Reducing the building density has more significant influence on mitigating the UHI effect, where reducing the building height and building density reduce the heat island degree-hours (HIdh) by about 20% and 30%, respectively. The relationships between the UHII and meteorological conditions vary among different periods. For example, the correlation between UHII and average wind speed is more significant in the winter and at night. Our results help to understand the relationships between regional climate conditions and the canopy layer UHI at the district scale.
Keywords: Canopy layer urban heat islands; Numerical model; Regional climate condition; Urban morphology.
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