Thermal and Geometric Effects on the Changing Rate of Surface Air Temperature in a Middle-Scale City

The changing rate of surface air temperature is different between urban and rural areas. The smaller changing rate in evening in the urban area forms the specific urban climate called a heat island, which typically appears in observations of calm fine winter days. Using a mesoscale model involving urban canopy physics, this work examines how the following four thermal and geometric factors, i.e., the anthropogenic heat (AH), heat capacity (HC), thermal conductivity (TC), and the sky view factor (SVF), modify the changing rate of surface air temperature in the urban area. The AH and TC are major contributors to modify the changing rate of urban air temperature in evening. In particular, the effect of AH is large and is localized around 18:00. On the other hand, the time when the HC and SVF contribute is different, i.e., HC is significant almost all night long, while the impact of SVF is concentrated in the afternoon. It would be effective for decreasing the urban air temperature to control the AH and to change the material of buildings.