Assessment of coastal inundation triggered by multiple drivers in Ca Mau Peninsula, Vietnam

Abstract. The Ca Mau Peninsula (CMP) plays a critical role in the agricultural and aquaculture productivity of the Vietnamese Mekong Delta (VMD), central to regional food security as well as the population's economic and social welfare. Unfortunately, the region faces persistent flood risks from seasonal Mekong flows and high tides. Climate change is expected to worsen these threats through sea level rise, extreme rainfall, and more frequent storm surges, while, human-induced factors such as land subsidence and riverbed lowering can further complicate the situation. Quantification of potential hazards associated with these drivers is therefore essential for shaping the future sustainability for the region and its ability to adapt to both current and forthcoming changes. In this study, we assess the impact of compounding hazards by developing regional inundation maps and analysing flood dynamics in the CMP using a large-scale hydrodynamic model encompassing the entire VMD. The model was enhanced with updated bathymetric data for major river channels, along with synchronized information on the dyke across the VMD from the 2018–2019 period, resulting in a substantial performance improvement. It was then applied across multiple future scenarios based on both individual drivers and their combinations, representing a wide but plausible range of anthropogenic and climate changes. Our findings show that upstream high flows, riverbed lowering, and occurrences of storm surges affecting the mainstream Mekong River have limited impact on regional inundation dynamics. However, land subsidence, rising sea levels, and their combined effects emerge as the primary drivers behind the escalation in both extent and intensity of the regional inundations in the future. These results, hence, are expected to serve as vital groundwork for strategic development and investment as well as for emergency decision-making and flood management planning, providing essential insights for shaping development policies and devising investment strategies related to infrastructure systems in this rapidly developing area.