<p>This study evaluates the salinity vulnerability of the Urmia coastal aquifer in northwestern Iran using the DRASTIC index and proposes an enhanced framework tailored for coastal settings. To address the limitations of the typical DRASTIC method, two coastal-specific parameters—hydraulic gradient (i) and distance to the shoreline (d)— were incorporated into the framework. Pearson’s correlation between vulnerability indices and water quality indicators (Cl, EC, and TDS) showed notable improvements with the extended framework, increasing from 0.46 to 0.75 for Cl, from 0.35 to 0.82 for EC, and from 0.33 to 0.79 for TDS. The highest correlation was observed between EC and the extended “DRASTIC-id” index, highlighting its enhanced predictive ability. The extended vulnerability map indicated very high to high vulnerability in the eastern and central parts of the Urmia aquifer and along the coastal margin, with lower values in the western zones farther from the lake. Sensitivity analysis of parameter removal revealed that the net recharge (R) parameter is among the most influential factors in the “Typical DRASTIC”, “DRASTIC-i”, and “DRASTIC-d” frameworks, while ‘i’ is most critical in the “DRASTIC-id”. Single-parameter sensitivity analysis confirmed ‘R’ as consistently important across all frameworks, with ‘i’ also emerging as a key driver in the “DRASTIC-i” and “DRASTIC-id”. The findings demonstrate that incorporating coastal-specific parameters significantly enhances the accuracy of vulnerability mapping and provides a more robust tool for sustainable groundwater management in salinity-prone aquifers.</p>