The possible impact of urbanization on a heavy rainfall event in Beijing

The impact of urbanization on a heavy rainfall event that occurred in Beijing on 21 July 2012 was investigated using version 3.6.1 of the Weather Research and Forecasting Model coupled with a multilayer urban canopy model. High-resolution land use data for Beijing in 2010 with modified urban parameterization were introduced into the model. Evaluation showed that the simulation result generally agreed well with observations. Two sensitivity tests with different urban high-resolution land use scenarios were employed to analyze the impact of urban expansion on this rainfall event. The simulation results confirmed that urbanization expansion played an important role in the distribution and intensity of precipitation for this extreme event. Urbanization led to total precipitation increasing in upstream and downstream directions. The start time of the precipitation process was advanced by 1 h, and the duration became longer due to the influence of urbanization. Moreover, urbanization caused the spatial distribution of precipitation to become more concentrated. The total precipitation amount above 250 mm and the frequency of precipitation intensity above 40 h(-1) mm are both increased. The results of this study show that urbanization plays a significant role in frontal-type rainfall.