[A-HW29] Climate, Rivers, and Floods: Exploring Hydro-Geomorphological Interactions

[AHW29-02] Enhancing Global Flood modelling with a Simplified Levee Module

★Invited Papers

*Gang Zhao¹, Dai Yamazaki², Yoshiaki Tanaka², Xudong Zhou³, Shuping Li², Yang Hu², Yukiko Hirabayashi⁴, Jeffrey Neal⁵, Paul Bates⁵ (1.The Institute of Science Tokyo, 2.University of Tokyo, 3.Ningbo University, 4.Shibaura Institute of Technology, 5.University of Bristol)

Keywords:Flood Hazard, Levee, River Hydrodynamics

Levees are critical infrastructure to mitigate flood hazards worldwide. Despite their importance, current global flood models inadequately account for levees due to the complexity of flow mechanisms involving levees and the lack of comprehensive levee data. This research aims to address these gaps by developing a levee module suitable for global flood modeling and proposing a reach-level parameterization approach to estimate the necessary levee parameters on a global scale. Specifically, we developed a simplified levee module based on the CaMa-Flood global flood model, requiring only two levee parameters: levee unprotected fraction and equivalent levee height. We then identified river reaches globally that are protected by levees and estimated the levee parameters for these reaches using open-access land use and levee standard data respectively. Finally, we evaluated the model's performance by comparing changes in river hydrodynamics and flood hazard maps, with and without levees, against observed data or official flood records from representative case studies. The results showed that (1) the proposed approach successfully identified globally protected reaches with a high hit rate of 91.3%; (2) the levee unprotected fraction can be accurately estimated based on open-access land-use data, and equivalent levee height can be derived from flood defense data using the global flood model; and (3) The enhanced CaMa-Flood model, incorporating the levee module, accurately simulated both river hydrodynamics and flood hazard mapping, improving the mean Nash-Sutcliffe efficiency of water levels from 0.68 to 0.84 and increasing the mean accuracy of flood hazard mapping from 76% to 87%.