Detecting topographic effect and urban signature in long-term summer rainfall trend in a complex urban environment

The influence of topography and urbanization on long-term summer rainfall trends in a complex urban environment is poorly understood. In this study, we utilized high-resolution gridding data (CN05.1) from 2416 long-term station observations (1960–2022) to investigate such influences over Wuhan, China. A geostatistical and mathematical framework was proposed to identify topographic and urban rainfall modifications in complex urban environments. The findings indicated that the topographic effect influences the region by causing it to experience drier conditions in dry years and wetter conditions in wet years, as well as increasing the frequency of light rainfall. Urbanization slightly suppressed light rainfall but amplified the intensity of other forms of rainfall, especially extreme rainfall. As impervious surfaces expanded, the urban precipitation-enhancing (UPE) effect diminished in the later stages of urbanization, particularly in urban and upwind areas, due to factors such as reduced evaporation (ET) and decreased relative humidity (RH). The relative contribution of urbanization to long-term rainfall trends was enhanced as urbanization increased, with increases ranging from 7 % to 40 %. This study demonstrates the potential of geostatistical and mathematical analysis techniques in elucidating the contributions of topography and urbanization to long-term rainfall patterns, leading to a better understanding of rainfall anomalies in complex urban environments.