Simulation of Compound Urban Flooding Using Direct Rainfall Modeling

Due to the recent impacts of climate change, the increasing concentration of localized rainfall events has led to a growing risk of inundation damage in urban areas. In urban centers where impervious surfaces are widely distributed, even short-duration rainfall can exceed the design capacity of stormwater drainage facilities, resulting in compound flood conditions in which pluvial inundation and river flooding occur simultaneously. To more realistically simulate these urban inundation characteristics, this study adopted a Direct Rainfall Modelling (DRM) approach and conducted an urban flood simulation for the Naengcheon watershed in Pohang City. The DRM approach directly applies rainfall to computational grid cells and integrates infiltration, surface storage, and overland flow processes based on the two-dimensional shallow water equations, thereby addressing the structural limitations associated with conventional subcatchment-based approaches. The analysis utilized observed rainfall time-series data recorded during Typhoon Hinnamnor in 2022, during which a total cumulative rainfall of 379 mm and a maximum hourly rainfall intensity of 91.2 mm/h were observed. The numerical simulation results indicated inundation depths of approximately 1.0–2.5 m along major road sections and in areas with concentrated commercial and residential functions, showing an overall spatial distribution consistent with actual flood conditions identified from CCTV footage and field survey data. In particular, the DRM approach demonstrated strong capability in representing the temporal evolution of inundation and the hydraulic connectivity between low-lying areas. These results suggest that DRM can provide a quantitative analytical basis for future urban flood mitigation planning and the management of flood-prone areas.

Acknowledgements: This work was supported by Electronics and Telecommunications Research Institute(ETRI) grant funded by the Korean government [25ZR1300, Development of Technology for the Urban Extreme Rainfall Response Platform]