Impact of urbanization on rainfall of different strengths in the Beijing area

Abstract

A weather research and forecasting model (WRF) coupled with a multilayer urban canopy model (BEP) was employed to assess the impact of urbanization on three rainfall processes of different strengths in Beijing. Based on the satisfactory model simulation performance, sensitivity tests based on a land use map without an urban component were performed to analyze the observed characteristics and the mechanisms underlying the influence of urbanization on rainfall of different strengths. The results showed that urbanization has the most significant influence on heavy rain among the three rainfall cases with different precipitation strengths and that urbanization obviously increased the amount of precipitation in urban areas and upwind and downwind suburban areas. At the edge of the city, moderate rainfall was also increased by urbanization. However, urbanization had almost no effect on light rainfall. A possible mechanism underlying the urbanization-induced change in precipitation is proposed. Urbanization results in changes in land use and increases in anthropogenic heat via changes in the energy balance of the surface, creating urban heat islands (UHIs). Consequently, cyclonic activity is more easily generated upwind and downwind of the urban area. When the moisture is sufficiently high, such as in cases of heavy or moderate rainfall, moisture flux convergence is more likely to develop in urban areas and the upwind and downwind areas. The rainfall system is enhanced in these areas as a result of the increase in the potential energy in the system.