• Long-term GALDIT analysis reveals persistent SWI vulnerability in the western coastal aquifers of Jeju Island, Korea. • Declining groundwater levels and rising electrical conductivity (EC) are identified as the primary drivers of high vulnerability in key monitoring wells. • Quantitative sensitivity analysis (SPSA and MRSA) validates the robustness of the model and highlights the dominant influence of the EC-based parameter on vulnerability index. Coastal aquifers on Jeju Island are highly vulnerable to seawater intrusion (SWI) due to their reliance on groundwater. This study applied the GALDIT index to assess SWI vulnerability by integrating six hydrogeological parameters. To track the dynamic changes, groundwater level and electrical conductivity data were collected from monitoring network that expanded from 30 wells in 2010 to 69 wells in 2024 across three watersheds. The results show a mean annual index of 6.15, with annual fluctuations ranging from -0.10 to 0.23. The robustness of the model was validated using Single-Parameter (SPSA) and Map Removal (MRSA) Sensitivity Analyses. SPSA identified hydraulic conductivity and aquifer thickness as the dominant factors governing the numerical baseline, with effective weights significantly exceeding their theoretical values. Conversely, MRSA revealed that the groundwater level is the primary driver of spatial distribution patterns, especially in inland areas. This sensitivity is less pronounced in coastal zones that have already reached a vulnerability saturation threshold. High-vulnerability zones were consistently concentrated along the southwestern coast, indicating persistent risks and the specific areas requiring long-term monitoring.
Yang et al. (Wed,) studied this question.