Abstract
As climate change drives global sea-level rise, coastal regions are increasingly vulnerable to compound hazards in which elevated baseline sea levels and tidal conditions can significantly amplify tsunami-induced inundation. This study quantitatively evaluates the impacts of sea-level rise (SLR) and tidal conditions on tsunami inundation in the Ise and Mikawa Bays in Japan using an integrated numerical framework consisting of JAGURS for tsunami propagation and SuWAT for inundation. Simulations were conducted under the 2050 SLR projections (+0.2 m and +0.5 m, SSP2-4.5), the annual maximum high-tide levels observed in 2012 (T.P. +1.29 m at the Port of Nagoya; T.P. +1.21 m at the Port of Mikawa), and the 185-day normal discharge for each target river. The results indicate that the influence of river discharge is negligible compared with the dominant effects of SLR and tides. In the inner Ise Bay, characterized by extensive low-lying plains, the combined effects of high tide and +0.5 m SLR increase the inundation area to 337% of the baseline. Mikawa Bay shows a similar vulnerability, with the inundation area increasing by a factor of 5.1 under high-tide conditions compared with the mean sea level. SLR increments from 0 m to 0.9 m were examined, and the results demonstrate an exponential increase in the inundation area with SLR magnitude in both bays. Regression analysis indicated that the nonlinear mechanism of inundation expansion—driven by levee overtopping and inflow into low-lying basins—is topographically robust across bay geometries. These findings indicate that future SLR may normalize extreme inundation risks previously associated with high-tide events. The developed empirical regression models provide a practical tool for rapid estimation of the extent of inundation without the need for exhaustive recomputation. The study offers guidance for revising coastal disaster mitigation strategies, evacuation planning, and reassessing infrastructure design standards in response to climate-driven environmental changes.