Two-thirds of global coastline affected by climate-driven saline groundwater intrusion by end of century, reaching far inland by 2300

Fresh groundwater is a vital resource along global coastlines where already over a third of the world’s population lives. Saline groundwater intrusion, driven by sea-level rise, groundwater abstraction, and reduced recharge, threatens the potability of coastal groundwater. Yet, the global potential for intrusion remains uncertain. Using a global groundwater model, we assess climate-driven saline groundwater intrusion along global coastlines until 2300 under a mild climate-change scenario. We find that two-thirds of the coastline will be affected by climate-driven intrusion of shallow groundwater between 2025 and 2100, and that it can locally intrude more than 9 km inland by 2300. While topography, aquifer thickness, and porosity define saline groundwater reach, climate-driven intrusion is mainly controlled by hydraulic conductivity and sea-level rise. We assess risk by combining intrusion, coastal populations, and groundwater use. Most populated coastlines will face a moderate risk, with high risk in the Mediterranean and South and East Asia.