Projected Changes in Southeast Asian Sea Surface Characteristics Using CMIP6 GCMs

Changing ocean properties threaten coastal communities and ecosystems worldwide. This study projected possible future changes in major sea surface attributes, including sea surface height (SSH), sea surface salinity (SSS), and sea surface temperature (SST) across the Southeast Asian Seas (SEAS) for shared socioeconomic pathways (SSPs) using Global Climate Models (GCMs) of Coupled Model Intercomparison Project Phase 6 (CMIP6). We employed Quantile Mapping (QM) to bias correct model outputs at the resolution of 0.25° considering the Ocean Reanalysis System 5 (ORAS5) data as the reference. The study identified four GCMs (CMCC-CM2-SR5, EC-Earth3, EC-Earth3-Veg, and NorESM2-MM) reliable for replicating observed sea surface characteristics. The bias-corrected top-performing GCMs revealed an increase in SSH ranging from 6 to 8 cm across most regions of SEAS during 1975–2014. The multimodel ensemble mean (MMEs) of the selected GCMs projected a 5–40 cm rise in sea level in most SEAS regions, with the most significant increases in the southern Gulf of Thailand and northern Peninsular Malaysia. Salinity and temperature projections show regional variations, with some areas seeing increases in salinity, and others may experience declines in the near future, with a significant decrease in far-future projections. The most concerning finding is the projected rise in sea surface temperature (up to 4.2 °C) in the Gulf of Thailand and the Strait of Malacca, potentially impacting marine ecosystems and fisheries. These findings highlight the urgency of robust adaptation plans to safeguard coastal communities and ecosystems from the multifaceted challenges of a warming climate.