The impact of the spatiotemporal structure of rainfall on flood frequency over a small urban watershed: an approach coupling stochastic storm transposition and hydrologic modeling

Abstract. The role of rainfall space–time structure, as well its complex interactions with land surface properties, in flood response remains an open research issue. This study contributes to this understanding, specifically for small (<15 km2) urban watersheds. Using a frequency analysis framework that combines stochastic storm transposition (SST)-based scenarios the physically based distributed Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model, we examine spatial and temporal variability across drainage basin scales highly urbanized Dead Run watershed (14.3 km2), Maryland, USA. results show complexities within several subwatersheds both short (<50 years) long (>100 return periods. impact impervious area on decreases increasing period. For extreme storms, maximum discharge is closely linked structure rainfall, especially core coverage. heterogeneity increases peak magnitudes by 50 % average at outlet large SST–GSSHA-coupled also highlights fact spatially are needed quick-response frequency, even relatively scales.