Understanding the impact of the built environment mosaic on rainfall-runoff behaviour

•Improves understanding of rainfall-runoff relationships in built urban environments.•An analysis of high-resolution monitoring of paired urban catchments is presented.•Urban rainfall-runoff relationships are complex, with urban mosaic form critical.•Improves understanding of urban heterogeneity’s influence on runoff.•Assumptions used in modelled urban rainfall-runoff are poorly replicated. Despite the importance of urban flooding, there are surprisingly few experimental studies of observed flood events from high-resolution hydrological data in urban systems to inform model development and parameterisation. The aim of this study was to understand how the interaction between rainfall and the layout of the built environment influences rainfall-runoff behaviour. A 2-year field campaign was undertaken to monitor rainfall runoff behaviour of two small (