Based on the high-resolution and long-term simulation, we find that extremely hot events occur most frequently in urban
area, where the Tmax (Tmin) exceeds 36oC (28oC) in around 40% (32%) of days. UHI effect at surface is more evident
during nighttime than daytime, with 20% of cases the UHI intensity larger than 2.5oC at night. However, The UHI affects
the vertical structure of PBL more deeply during daytime than nighttime. Net gain for both LH and NR is larger over urban
than rural area during daytime. Correspondingly, the net loss of SH and GH at surface are larger over urban area than rural area resulting from warmer skin temperature over the urban surface. Because of different diurnal characteristics of urban-rural differences in LH, GH and other energy fluxes, the near surface UHII exhibits a very complex diurnal feature. We find
a negative correlation between UHII and wind speed, with a
correlation coefficients of −0.67, suggesting a strong UHI
effect at lower-wind speed synoptic condition. We also find the
UHI effect is lower under cloudy or rainy days.