Street-scale storm surge load impact assessment using fine-resolution numerical modelling: a case study from Nemuro, Japan

Due to gradual sea level rise and changes in the climate system, coastal vulnerability to storm surge hazards is expected to increase in some areas. Studies regarding the effect of storm surge inundation on buildings and human lives, especially when it comes to relatively low-threat level events, have been few, however. In this research, storm surge load impact around coastal residential areas was quantitatively assessed, through fine-resolution numerical modelling. Meso- and street-scale simulation results for a storm surge event in Nemuro, Japan, were comprehensively validated against observations and field measurements, and the simulation results showed good accuracy for sea level, significant wave height and inundation area. A fine-resolution, street-scale coastal flood simulation was carried out with individual and grouped buildings, created with a building block model, and the results showed the significant role of buildings by realistically capturing inundation dynamics. Hydrodynamic results showed that coastal flood impact on buildings was insignificant (consistent with surveys). Lastly, the potential flood impact on people in the streets was investigated, using five human instability equations, where the most pessimistic results showed average values between 0.0 and 0.2 (max 0.6-0.7), and slightly below 0.4 for children and the elderly, respectively. These values indicated that threat levels during the Nemuro storm event were low, which corresponded with observations (no fatalities). This study framework could be applied wherever an accurate local storm surge threat estimate was required.