Assessment of future possible maximum flooding extent in the midwestern coastal region of Taiwan resulting from sea-level rise and land subsidence

Abstract

While land subsidence (LS) caused by groundwater overuse is a significant contributor to inundation in coastal areas, rising sea levels remain the critical factor affecting coastal flooding globally. In this work, we projected potential inundation areas on the midwestern coast of Taiwan in 2100 using a high-resolution numerical model with light detection and ranging (LiDAR)-based digital elevation data. Two simulation approaches, namely, constant spring tide (CST) and dynamic astronomical tide (DAT) approaches, were employed to pair various sea-level rise (SLR) magnitudes from the 6th Assessment Report of IPCC with LS magnitudes reported by the Water Resource Agency of Taiwan. The CST method always projected larger maximum inundation areas (MIAs) than the DAT method. However, the discrepancies in the MIA projections between the CST and DAT methods showed exponential decay as the SLR magnitude increased. Through 1320 scenario simulations, the projected worst-case median MIAs derived using the CST and DAT methods were approximately 1100 and 1000 km2 in the year 2100, respectively, and the synergistic effect of SLR and LS significantly exacerbated the coastal inundation. This study indicates that the DAT approach is more realistic than the CST approach for modelling actual tidal variations and is suitable for assessing coastal inundation due to rising sea levels and subsiding lands worldwide.