A Numerical Simulation of Urban Heat Island Effect in Kunming

This paper uses the coupling Noah/Single-layer Urban Canopy scheme coupled with WRF (V3.9.1) model is used as a Control experiment to investigate the effects of land-use type (Md04 experiment), land surface process (NoUCM experiment), and lake (Nolake experiment) on the intensity of urban heat island, and the horizontal and vertical spatial distribution characteristics of urban meteorological elements in Kunming. The following are the main findings: (1) In all four experiments, the average daily variation trend of urban heat island intensity is almost similar. The urban heat island (UHI) intensity is low during the daytime and high at night, peaking at around 2000 BJT (Beijing time). The average daily maximum difference for Control-NoUCM (Nolake) is −0.79°C (+1.07°C). (2) The difference of the sensible heat (latent heat) flux is +46.18 (−79.71) W m⁻² based on the energy balance equation analysis of the Control-Md04 experiment, and the release of latent heat flux is greater than the absolute value of the sensible heat flux. In the Control-NoUCM experiment, the sensible heat (latent heat) flux difference is −40.88 (+29.60) W m⁻². The NoUCM experiment does not take into account the heat storage and shielding of geometric buildings. The land surface absorbs the majority of solar radiation, resulting in a large absolute value of the sensible heat flux. (3) The boundary layer height reaches its maximum (minimum) value at 1500 (0700) BJT in all four experiments. The height of the urban boundary layer decreased by approximately 103 m (32 m) in NoUCM (Nolake), while it increased by approximately 102 m in Md04 experiment. (4) The numerical simulation results of the influence of the lake (Dianchi lake) on the circulation of urban heat islands show that the vertical movement over the lake is weak, but the horizontal lake-land breeze is strong. The breeze’s circulation benefits from the transportation of water vapor to the city center, which increases the humidity of dry air and enlarges the water vapor content. Furthermore, it increases the release of latent heat flux and reduces the sensible heat flux and the temperature gradient.