Urbanization influence on changes of extreme precipitation in mainland China

Extreme precipitation events have caused obvious damage to human environments and socioeconomic systems. However, the changes in extreme precipitation and their underlying causes remain unclear. This study analyzed daily precipitation data from 2,254 meteorological stations across China from 1981 to 2018, focusing on two key extreme precipitation indicators: Max 1-day precipitation amount (Rx1day) and Max 5-day precipitation amount (Rx5day). Trend analysis was conducted for 17 river basin divisions using the Mann-Kendall method. We also applied the field significance test, a statistical method to evaluate whether a spatial pattern of locally significant results, to determine whether observed trends at individual stations were statistically significant or due to random variation. The results showed that 59.3% and 58.6% of the stations exhibited increasing trends in Rx1day and Rx5day, respectively, with significant trends identified at 5.4% and 4.1% of the stations. The field significance test revealed a significant increasing in Rx1day across China at the 5% significance level. Among the 17 sub-basins, significant increases in extreme precipitation were observed in the Inland rivers of Xinjiang and Northern Tibet. The result was consistent with the warming and humidification trends in northwest China. We further analyzed the relationship between urbanization and extreme precipitation by using population density to distinguish rural and urban stations. We found that the spatial distribution of urban stations closely overlapped with stations experiencing increased extreme precipitation, while rural stations corresponded with those showing a decrease. With the progress of urbanization, variations in the trends observed at urban and rural stations have emerged. Nevertheless, urban stations exerted a more pronounced influence on the increasing trend of extreme precipitation.