Impact of urbanization on hourly precipitation in Beijing, China: Spatiotemporal patterns and causes

Human-induced impacts, such as urbanization, on regional climate changes and precipitation changes in particular have been attracting increasing international interests. However, there are different evaluations of urban effects on precipitation changes in both space and time. In this study, taking Beijing Municipality (BJM) as a case study, the hourly precipitation data from 20 automatic weather stations for a period of 2011-2015 were analyzed using the circular statistical analysis and grange causality test technique. Changes in precipitation intensity, amount, duration, and timing were investigated, and extreme precipitation indices were defined by percentiles and consecutive precipitation processes. Results indicated that impacts on precipitation varied with the type of urbanization. Urban areas with the highest population density were dominated by the slightly longer precipitation duration, higher precipitation intensity and larger precipitation amount with lengthening consecutive dry days. Therefore, urbanization has the potential to intensify precipitation processes. In addition, due to varying topographical features in the vicinity of BJM, complicated precipitation changes can be identified along two sides of the urban area. Larger precipitation amount and higher precipitation intensity can be found along the western side than along the eastern flank of the BJM. Further, higher precipitation amount can be observed in the downwind areas. High-level urban heat island can trigger more pronounced urban precipitation islands which lags behind the UHI. What's more, urban high buildings can benefit slowing down air mass, hence lengthening precipitation events. These results provide useful information for management of urban activities, and offer a new viewpoint for further understanding of the urban precipitation island (UPI) effect.