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• A 2D hydrodynamic overland model for the highly urbanized area. • Distributing rainfall and infiltration directly on the overland cell. • Two connections with the sewer model for different sewer data availability. • Physical connection applied for the area with sufficient sewer data. • Conceptual connection applied for the area without sufficient sewer data. Hydrodynamic models have been increasingly applied to urban flood simulations, but still encounter challenges because of complicated urban landscapes, buildings and structures, as well as insufficient sewer data. In order to improve the applicability in real-life urban environments, a distributed hydrodynamic model for urban storm flood risk assessment (DHMUrban) is developed in this study. It is based on the two-dimensional shallow water flow equations simplified by neglecting the convection terms in the momentum equations. The sharp variation of ground surface often happening in urban areas is specially treated with the broad-crested weir flow equation. The rainfall, infiltration and sewer drainage are considered at each overland cell. Two connection approaches between the overland model and the sewer model are proposed depending on the availability of sewer data. The overland cells and the sewer nodes are connected physically in areas with complete sewer data, and connected conceptually through a drainage relationship in areas where sewer data are insufficient or unavailable. The present model has been evaluated in five cases, showing comparable reliability and stability. It has been applied to a real-life urban catchment in Shenzhen City, and demonstrated to be capable of presenting well the ground surface flooding, adapting adequately to the real-life urban areas with different data availability and providing practical and reliable solutions for urban storm flood risk assessments. [ABSTRACT FROM AUTHOR]