Simulation Study of Urbanization Impact on Climate in Chengdu

To study the impact of urbanization on the local climate in Chengdu, the urbanization effects during summer and winter over Chengdu are simulated by using data about the underlying surface land use type of different periods and the WRF (Weather Research and Forecasting) model, coupled with a single-layer urban canopy model (UCM). The main conclusions are drawn as follows. First, in summer, the urbanization of Chengdu causes a temperature-increasing area over the urban area. The surface temperature increases by about 2.8°C in the urban area, and the boundary layer height increases by about 150 m. In winter, the surface temperature increases by about 0.6°C in the urban area, and the boundary layer height by about 25 m. In addition, the diurnal temperature range in both summer and winter decreases. Second, during summer and winter, the 2-m relative humidity decreases, while the sensible heat flux increases and the latent heat flux decreases due to the impact of urbanization, but the degree of change in summer is stronger than in winter. Third, during both seasons, the wind speed decreases by around 0.1–0.6 m s⁻¹ in the urban area due to an increase in surface roughness, but the area where the wind speed decreases in summer is larger than in winter. Due to urbanization, in the lower atmosphere over the city, divergence decreases, convergence and vertical velocity increases, while water vapor is transported significantly from the lower layer to the upper layer in summer. Finally, during summer, because of urbanization, the average daily precipitation and daytime precipitation both increase in the urban upwind and downwind directions. On the other hand, nighttime precipitation increases in urban downwind areas, but it has no significant effect on urban upwind areas.