Integrated methodology for urban flood inundation modeling: a case study of Ichinomiya River Basin, Japan

Important cities in the low-lying region of the Ichinomiya River basin have experienced severe inundation in the past as a result of heavy downpour. Therefore, modeling the potential impact of floods within the river basin is extremely important for future flood disaster risk reduction and adaptation plans. Flood risk analysis requires adequate understanding of the potential hazard’s characteristics and their potential impacts on the environment. Rainfall of the study area (from 1996 to 2014) was characterized using Gumbel distribution to determine the Intensity, duration frequency (IDF) of rainfalls. An integrated grid-based approach (Hydrodynamic (Flo 2D) and height above nearest drainage (HAND) models) to predict the potential flood intensity and hazard zones in Ichinomiya River basin, Chiba prefecture, Japan. Rainfall analysis revealed a decrease in the intensity of rainfall within the selected years. However, there is possibility of experiencing extreme events in the future due to climate change. Results of Flo 2D and HAND models agreed in terms of the flood extents and areas affected by flood in the area, with the potential flood hazard zone advance towards the north east and within the depressed/lowland areas. Future extreme events showed potential high risk of floods, especially in the downstream parts of the basin. The outputs of the flood models can serve as tools for decision making in future flood disaster risk reduction plans.