Advanced statistical analyses of urbanization impacts on heavy rainfall in the Beijing metropolitan area

Abstract

To identify the rainfall changes induced by urbanization, the spatiotemporal patterns of L-Moment statistics, homogeneous regions, design rainfall and heavy rainfall were investigated in different stages of urbanization. The results suggested that L-Cv, L-Skewness, and L-Kurtosis were higher in the urban region than in the surrounding suburbs (averages of 0.69, 0.54, and 0.29 vs 0.66, 0.51, and 0.27, respectively). This indicated that more frequent extreme rainfall occurred in the urban region with higher variability. Moreover, the number of hydrologically homogeneous regions in Beijing increased from two to three after the rapid urbanization since 1998. The increasing rainfall intensities for different return periods with accelerated urbanization were observed. For a 50-year return period, the increased intensities ranged from 9 to 41%, with more substantial increase over the western urban region. Notably, the center of annual days of heavy rainfall has moved towards the built-up area during the rapid urbanization period. The spatial patterns of rainfall intensity showed variations in another way: the center moved to the urban area adjacent to the western mountain. A possible interpretation of these findings was that the area influenced by the urban heat island expanded considerably in Beijing. This study suggested that the engineering design should consider not only the change of impervious areas, but also the urbanization impacts on rainfall in order to combat the flooding risks.