Impact Of Urbanization On Spatial And Temporal Variation Of Rainfall In Beijing Over The Last 50 Years

Rainfall is one of the key terms involved in many hydrological processes, and it is particularly important in the field of urban hydrology. It is well known that urbanization can have potential impact on precipitation process due to the changes it causes to the ground roughness, thermal-dynamics and many other factors. In this study, the focus is set on the impact on the precipitation patterns in Beijing in term of spatial and temporal variation, from the urbanization over last 50 years in which time the fast and continuous expansion of the city at dramatic scales, the rapid growth of residents population as well as human activities especially building of ground constructions, collectively and inevitably bring changes to the local climatic characteristics of the urbanized areas. This study looks at the two periods according to the speed of urbanization, namely the slow urbanization period of 1957-1980 and the fast urbanization period of 1981-2010. Rainfall data collected from the representative rain gauges across the region is used to analyze the spatial and temporal variation over these two periods. The results show that precipitation in urban areas exhibits the characteristics of higher intensity, shorter duration, with the rainfall mainly concentrated in 60 min or so. Local short-duration rainstorms tend to occur more frequently. Compared with suburban areas, urbanization has significant effect, especially on short-duration precipitation events evidenced by remarkable difference between the coefficients of variation of urban rainfall and those of the suburbs. In addition, for the fast urbanization period, the spatially localized, highly intensive rainfall events are found to be more frequent. Therefore, urbanization of the city has caused increase of the strong convective weather and pressure of flood control drainage, which should be paid more attentions to in city planning