Urban signatures of sub-daily extreme precipitation events over a metropolitan region

Abstract

Previous research on the relationship between urbanization and extreme precipitation has shown that regional and global anthropogenic changes have made extreme precipitation events more frequent. The purpose of this research was to explore changes in the variability of extreme precipitation in urban areas that underwent different degrees of urbanization intensity, and to explore the possible reasons using data from 7 meteorological stations in Shenzhen, China with hourly precipitation records dating back to the 60's. Shenzhen is one of the fastest growing metropolitan areas on earth with heavy urbanization occurring since 1979. We used k-means clustering to categorize areas of the city into steadily urbanized regions (SUR) or rapidly urbanized regions (RUR). Next, the variations in the linear trends of annual maximum precipitation (AMP) were analyzed, followed by water vapor analysis and the random forest algorithm to analyze the causes of the variation. The results showed that the severity of the urbanization process had a large and significant impact on extreme precipitation. The AMP analysis showed that at the higher temporal resolutions (< 6 h) extreme precipitation was only significant at RUR stations, while at low temporal resolutions precipitation did not significantly change at any station. An analysis of the diurnal patterns of precipitation and the water vapor analysis over Shenzhen showed that the increase in short-duration extreme precipitation events may be related to atmospheric instability caused by heat emitted as a byproduct of the urbanization process. Furthermore, the differences between the variations in the precipitation trends of SUR and RUR may be related to differences in thermal contrast between high and low altitudes. The results of the random forest analysis supported the correlations between the severity of urban development and changes in precipitation variability. Our findings have highlighted the need for a better understanding of the local and regional anthropogenic effects on the climate and the intensification of extreme climate events due to urbanization.