Future Sea-Level Rise in Southeast Asia: New Insights on Uncertainty, Ocean Dynamics, and Extreme Events

Future sea-level rise will generate hazards for coastal populations, economies, and infrastructure in Singapore and Southeast Asia. However, regional projections remain highly uncertain due to complex regional to local factors, including ocean dynamics, and extreme sea-level events. Here, we review our 4-year project funded by Singapore’s National Sea Level Programme, which focused on enhancing the accuracy of regional sea-level rise projections by 2100. Our approach includes: 1) attributing historical sea-level changes to anthropogenic and natural forcings[1]; 2) quantifying drift uncertainty in global climate model simulations[2]; 3) investigating tide-surge interaction in Singapore and surrounding regions[3]; and 4) addressing ambiguity in sea-level rise projection by fusing multiple projections used in the Intergovernmental Panel on Climate Change 6^th Assessment Report (IPCC AR6)[4]. First, using large ensemble climate model simulations we detected and attributed historical (1950–2014) sea-level changes over the Indo-Pacific warm pool region providing insights for future projections. We discovered that the historical rise in sea level is predominantly driven by the influence of greenhouse gases, although aerosols tend to moderate the rate of rise. Notably, the rate of sea-level rise and the time of emergence of anthropogenic signals vary spatially in the region. We also highlight the important role of manometric sea-level changes in shallow and coastal regions in Southeast Asia. Second, we develop a Monte Carlo drift correction technique to quantify uncertainty in drift correction for global climate models, using climate model data. Our findings highlight that drift uncertainty can significantly impact energy balance estimates and sea-level rise, underscoring the need to account for drift uncertainty when analyzing climate model outputs. Third, using a statistical framework, we study tide-surge interaction at seven tide gauges along the coast of Singapore and the east coast of Peninsular Malaysia, focusing on the timing of extreme non-tidal residual relative to tidal high water. We found that tide-surge interaction influences coastal water levels in this region, and our semi-empirical model provides insight into the mechanisms of tidal phase alteration. Finally, we propose a new approach to quantify the best estimate of the scientific uncertainty associated with sea-level rise by fusing the complementary strengths of the ice sheet models and expert elicitations used in IPCC AR6. Under a high-emissions scenario, the very likely range is 0.5–1.9 m. The 95th percentile projection of 1.9 m can inform a high-end storyline, supporting decision-making for activities with low uncertainty tolerance. We plan to use our findings to offer policymakers and coastal planners a robust, high-confidence toolset for long-term adaptation strategies in Singapore and Southeast Asia.

[1] Samanta et al., (2024), https://doi.org/10.1029/2023EF003684

[2] Grandey et al., (2023), https://doi.org/10.5194/gmd-16-6593-2023

[3] Koh et al., (2024), https://doi.org/10.5194/os-20-1495-2024

[4] Grandey et al., (2024), https://doi.org/10.1029/2024EF005295