Effect of Urbanization on Extreme Precipitation Events in an Urban Agglomeration in the Middle Reaches of the Yangtze River

Investigating changes in extreme precipitation events in large urban agglomerations is important for understanding their evolution and mitigating the associated damage. Based on observational data from 49 meteorological stations in the Urban Agglomeration in the Middle Reaches of the Yangtze River (UAMRYR) from 1985 to 2020, this study employed Sen's slope estimation, the Mann–Kendall test, regression models and a dynamic urban–rural station classification method to examine the spatiotemporal variations in extreme precipitation events and their relationship with urbanization. The results showed that: (1) Except for the maximum number of consecutive dry days (CDDs), the extreme precipitation indices generally exhibited increasing trends. Monthly maximum 1‐day precipitation (Rx1day), monthly maximum 5‐day precipitation (Rx5day) and annual total precipitation from days above the 99th percentile (R99p) increased significantly at rates of 0.42, 0.48 and 1.18 mm/a, respectively, whereas CDD decreased significantly at a rate of 0.15 days/a. These changes also exhibited considerable spatial heterogeneity. (2) Extreme precipitation indices at urban and rural stations generally showed consistent directions of change; however, the trends at urban stations were generally greater in magnitude and more statistically significant than those at rural stations. The urbanization impacts on SDII, Rx1day and Rx5day were 4.79 mm/day/a, 0.52 mm/a and 1.30 mm/a, respectively, with urbanization impact contribution rates exceeding 60% for all three indices. (3) Compared with the global ordinary least squares (OLSs) regression model, the local geographically and temporally weighted regression (GTWR) model better captured the spatially varying relationship between the impervious area (IA) ratio and extreme precipitation events. IA was significantly and positively associated with Rx1day and R99p in highly urbanized areas, such as the Wuhan metropolitan area and at Zhuzhou Station and with Rx5day in the Poyang Lake City Cluster. Overall, urbanization was more strongly associated with changes in the intensity of extreme precipitation events in the UAMRYR and this relationship exhibited pronounced spatial heterogeneity.