Numerical study of the Chongqing high-density buildings environment by the WRF with the different urban canopy schemes

The three urban canopy schemes were coupled in the Advanced Research Weather Research andForecasting (WRF) model, including the single-layer Urban Canopy Model(UCM), the multi-layer Building Environment Parameterization(BEP) scheme and the Building Environment Model based on BEP (BEP+BEM). Both the mechanism of urban land surface exchange and urban parameters setting are different from each other in these schemes, so it is very important to discuss whether the schemes and urban parameters setting are able to simulate the urban heat environment accurately for the urban with high density buildings and complex underlying surface in china. Also, evaluating the different scheme performance and investigating the building morphologic parameters sensitivity for urban heat environment simulation were worthy questions. In this paper three cases by selecting different urban canopy scheme in the WRF model were addressed for Chongqing City under continuous hot weather background in summer, and two group sensitive cases were designed to investigate the buildings' morphological parameters sensibility.The main results are as follows: (1)With the high resolution GIS data supported, the simulation result of BEP+BEM scheme is the best.The RMSEs between observation and simulation of BEP+BEM,BEP and UCM scheme are 1.3℃, 1.4℃, 2.1℃, respectively. The simulated air temperature at 2 m was more consistent with the observation by automatic weather stations than by national basic stations.(2)Building height and density parameters have obviously influence on near surface air temperature.The building height increasing gives rise to the aspect ratio enlargement, then the short wave shielding is more distinct, which lead the air temperature at 2 m to reducing by the maximum of o.4℃. While for the more heat storage in urban canopy owing to radiation trapping at night air temperature at 2 m increased significantly, up to 0.7℃. With the increase of buildings' density, the air temperature at 2 m decreased in daytime and increased at night too, for the the aspect ratio changes with the same trend as the building's height increasing.(3)The best parameters are 20 m for building interval and 20%(15 m)+60%(20 m)+20%(25 m) for building height. If so, the RMSE decrease from 1.3℃ to 0.6℃.