Spatial heterogeneity of controlling factors’ impact on urban pluvial flooding in Cincinnati, US

Urban pluvial flooding has become a common threat for urban areas. Intensified rainfall, increasing imperviousness, and insufficient drainage capacity contribute to the increase of pluvial flood risk. The strategy of risk mitigation relies on the understanding of these controlling factors of urban pluvial flooding. However, spatial heterogeneity of the impacts of controlling factors has received limited attention. This study analyzes how topography, rainfall, impervious surfaces affect urban pluvial flooding and how the effects vary in space. A case study in the city of Cincinnati, US based on four storm events in recent years is conducted. The impact of topography is measured by a depression-based empirical parameter, Topographic Control Index (TCI), which is generated based on depression ponding volume, contributing area, and upstream slope. Rainfall depth estimated from kriging interpolation method is used to measure how the rainfall affect the urban pluvial flooding. The impervious area ratio of the contributing area of each depression as well as that of observed flooded locations are calculated to analyze the influence of impervious area. The results showed that TCI value and rainfall intensity are spatially correlated with the presence of flooded locations, and flooded locations can be classified into two types: rainfall control or topography control. The imperviousness of land surface does not show a significant correlation with pluvial flood due to the relatively small spatial variation of impervious area in a well-developed city. The framework in this study could identify the spatial distribution of dominant controlling factors for pluvial flooding, which is critical for the effective planning of mitigation measures.