<p>An integrated geospatial, hydrogeochemical framework for identifying environmentally suitable locations for solar-powered green hydrogen production along Egypt’s northwestern Mediterranean coast is applied. The methodology combines environmental stable isotope of groundwater (δ¹⁸O and δ²H) for quaternary, upper miocene, and lower miocene aquifers with multi-criteria spatial analysis in geographic information system (GIS). Isotopic signatures are used to evaluate groundwater recharge sources, salinization processes, and the extent of seawater intrusion providing a quantitative basis for assessing aquifers vulnerability. Eight spatial criteria, elevation, slope, aspect, land use/land cover, proximity to roads, proximity to the shoreline, hydraulic head, and seawater intrusion index, are weighted using fuzzy-analytic hierarchy process (AHP) and integrated to generate site suitability map for hydrogen infrastructure development. The results classify the study area into five suitability zones, with central and northeastern sectors emerging as the most favorable due to high solar potential, lower groundwater vulnerability, and adequate accessibility. Environmentally constrained zones are primarily associated with low hydraulic heads and pronounced seawater intrusion near the coast. At the regional scale, the framework supports informed decision-making for sustainable hydrogen deployment while minimizing impacts on fragile coastal aquifers. More broadly, the study demonstrates the value of coupling isotope hydrology, hydrochemistry and environmental parameters with GIS-based decision analysis, offering a transferable approach for siting renewable hydrogen projects in arid and semi-arid coastal regions worldwide.</p>