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The Beijing-Tianjin-Hebei region experienced the most rainfall in 1994 and the least rainfall in 1997 during the last 20 years. Utilizing the Weather Research and Forecasting (WRF) model coupled with a single-layer urban canopy model (UCM), we investigate the possible effects of urbanization on summer precipitation under different climate backgrounds using the two extreme years. By comparing the results of control and sensitivity runs, we find totally different effects in the 2 years. In 1994, the rainfall and rainfall frequency decrease in most areas due to urbanization, and decreases in the rainfall intensity occur in urban areas of Beijing, Tangshan, and Shijiazhuang. In 1997, the rainfall, rainfall frequency, and intensity are reduced in southwest of Beijing-Tianjin-Hebei, while the change is opposite in northeast. Urbanization alters the diurnal distribution of rainfall, the energy budget, and the water vapor content in the atmosphere. Due to the decrease in city evaporation and transpiration, the surface latent heat flux is reduced. The water vapor mixing ratio in urban area decreases apparently from surface to 850 hPa, while it increases from 850 to 600 hPa. Overall, the reduction of water vapor mixing ratio in 1994 is more than that in 1997, which implies that the “dry island effect” caused by urbanization is stronger in the wet year than that in the dry year. Results also show that the inhibition (enhancement) of deep convection may explain the modification of precipitation. [ABSTRACT FROM AUTHOR]

To ensure successful hosting of the 2022 Olympic Winter Games, a comprehensive understanding of the wind field characteristics in the Chongli Mountain region is essential. The purpose of this research was to accurately simulate the microscale wind in the Chongli Mountain region. Coupling the Weather Research and Forecasting (WRF) model with a computational fluid dynamics (CFD) model is a method for simulating the microscale wind field over complex terrain. The performance of the WRF-CFD model in the Chongli Mountain region was enhanced from two aspects. First, as WRF offers multiple physical schemes, a sensitivity analysis was performed to evaluate which scheme provided the best boundary condition for CFD. Second, to solve the problem of terrain differences between the WRF and CFD models, an improved method capable of coupling these two models is proposed. The results show that these improvements can enhance the performance of the WRF-CFD model and produce a more accurate microscale simulation of the wind field in the Chongli Mountain region. [ABSTRACT FROM AUTHOR]