Study Warns Saltwater Intrusion Threatens Global Coastal Groundwater by 2100

Underground saltwater intrusion is expected to severely affect three out of every four coastal regions globally by the year 2100, according to findings published in Geophysical Research Letters. The research, a collaboration between NASA's Jet Propulsion Laboratory (JPL) and the U.S. Department of Defense, highlights significant risks to freshwater resources in coastal aquifers due to rising sea levels and reduced groundwater recharge. The U.S. Eastern Seaboard and other low-lying regions have been identified as some of the most vulnerable areas.

Saltwater Intrusion and Its Mechanisms

The phenomenon, known as saltwater intrusion, occurs beneath coastlines, where freshwater from aquifers and seawater naturally balance each other. Sea level rise, driven by climate change, is increasing the pressure of seawater against land, while slower groundwater recharge due to reduced rainfall weakens the inland flow of fresh water. This shift disrupts the delicate balance, allowing seawater to move further inland, threatening water quality and ecosystem health.

Global Impact and Key Findings

As per the study, saltwater intrusion is projected to occur in 77 percent of the coastal watersheds examined. Rising sea levels alone are expected to influence 82 percent of these areas, causing the transition zone between fresh and salt water to move up to 200 metres inland. Conversely, decreased groundwater recharge will impact 45 percent of regions, with the transition zone extending as far as 1,200 metres inland in some cases, particularly in arid regions such as the Arabian Peninsula and Western Australia.
Lead author Kyra Adams, a groundwater scientist at JPL, explained in a press release by NASA that the primary driver of intrusion—whether sea level rise or reduced recharge—varies by location, influencing management strategies. For instance, areas impacted by low recharge may benefit from protective measures for groundwater resources, while regions facing sea level-induced risks may consider redirecting groundwater supplies.

Implications for Vulnerable Regions

The research used data from the HydroSHEDS database and incorporated a model accounting for groundwater dynamics and sea level rise. Co-author Ben Hamlington of NASA's Sea Level Change Team noted that the findings align with global coastal flooding patterns, underscoring the compounded risks posed by rising sea levels and changing climatic conditions.

Hamlington told NASA that nations with limited resources face the highest risks, highlighting the importance of global frameworks to address these challenges.