Effects of Physical Urbanization and Natural Topography on the Spatiotemporal Variability of Extreme Precipitation: A Case Study of the Zhengzhou Metropolitan Area, China

Global warming has intensified the hydrological cycle and increased the frequency of extreme precipitation events. However, the localized impacts of rapid physical urbanization on extreme precipitation remain insufficiently quantified, particularly at the metropolitan scale. This study investigates the spatiotemporal dynamics and driving mechanisms of extreme precipitation in the Zhengzhou Metropolitan Area, a rapidly urbanizing region in central China. Daily precipitation records from 51 meteorological stations during 1985–2021 were used to calculate 11 extreme precipitation indices, including annual total wet-day precipitation (PRCPTOT) and maximum 5-day precipitation (Rx5day). Eight physical urbanization indicators and two topographic indicators were selected as explanatory variables. Spearman correlation analysis and Geographically and Temporally Weighted Regression (GTWR) were applied to examine the spatially and temporally heterogeneous relationships between physical urbanization, topography, and extreme precipitation. The results show that PRCPTOT increased by 1.12 mm per decade, while Rx5day increased by 0.43 mm per decade. Spatially, prolonged but relatively low-frequency precipitation events were mainly distributed in the western mountainous areas, whereas high-intensity extreme precipitation was concentrated in the eastern plains. Across the five temporally matched cross-sections, the associations between physical urbanization-related landscape indicators and precipitation intensity became more evident beginning in 2005, although their magnitude and statistical significance varied among years. The GTWR model explained 89% of the variation in PRCPTOT, indicating strong explanatory power for the combined effects of physical urbanization and topography. Physical urbanization-related landscape patterns and topographic factors showed distinct and temporally varying associations with extreme precipitation across the Zhengzhou Metropolitan Area. These findings deepen the understanding of physical urbanization–precipitation interactions and provide scientific support for flood-resilient urban planning and climate-adaptive spatial governance in rapidly urbanizing metropolitan regions.