Ryuto Ugajin, Yoshiyuki Yokoo, Takahiro Sayama, Sheikh Hefzul Bari, Chris Leong
Received 10 October, 2025
Accepted 12 January, 2026
Published online 18 April, 2026
Ryuto Ugajin1), Yoshiyuki Yokoo2)3), Takahiro Sayama4), Sheikh Hefzul Bari1), Chris Leong5)
1) Graduate School of Symbiotic Systems Science, Fukushima University, Japan
2) Faculty of Symbiotic Systems Science, Fukushima University, Japan
3) Hydrogen Energy Research Institute, Fukushima University, Japan
4) Disaster Prevention Research Institute, Kyoto University, Japan
5) Linkage Project, Research Institute for Humanity and Nature, Japan
Growing flood severity demands numerical experiments on watershed-scale rainfall-runoff-inundation processes, to properly evaluate and develop effective practical measures. Hence, the Rainfall-Runoff-Inundation (RRI) model has been continuously developed to enhance simulation accuracy. Unfortunately, conventional RRI implementations often blur rivers and floodplains at the grid scale and do not distinguish left and right banks, limiting the spatial accuracy of inundated areas. Thus, we extend the RRI model to: (1) separate inundation calculations of the left and right banks, (2) allocate rainfall falling on river cells to the channel water balance, and (3) explicitly and spatially represent the river channel width exceeding the model resolution to improve the accuracy of estimating the spatial distribution and the depth of inundated areas as well as river discharge. The results show that explicitly representing the channel width improves the accuracy of simulated river discharge, inundation extent and relative spatial characteristics of depth. Consequently, our revised RRI model yields more realistic outputs than conventional flood control models.
Copyright (c) 2025 The Author(s) CC-BY 4.0
