Saltwater intrusion threatens global coastal groundwater by 2100, study warns

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

Salt water intrusion and its mechanisms

This phenomenon, known as salt water intrusion, occurs beneath the coastline, where fresh water and sea water from aquifers naturally balance each other. Sea level rise due to climate change is increasing seawater pressure on land, while slower groundwater recharge due to less rainfall is weakening inland flows of fresh water. This change disrupts the delicate balance, causing seawater to move inland, threatening water quality and ecosystem health.

Global impact and key findings

According to the study, salt water intrusion is estimated to occur in 77 percent of the examined coastal wetlands. Rising sea levels alone are expected to affect 82 percent of these areas, pushing the transition zone between fresh and salt water up to 200 meters inland. In contrast, reduced groundwater recharge would affect 45 percent of areas, with the transition zone extending up to 1,200 meters inland in some cases, particularly in arid regions such as the Arabian Peninsula and Western Australia.
Kyra Adams, lead author and groundwater scientist at JPL, explained in a NASA press release that the primary driver of intrusion — whether sea level rise or reduced recharge — varies by location, which affects management strategies. For example, areas affected by low recharge may benefit from protective measures for groundwater resources, while areas facing sea level-induced risks may consider redirecting groundwater supplies.

Implications for vulnerable sectors

The research used data from the Hydrosheds database and included a model accounting for groundwater dynamics and sea level rise. Co-author Ben Hamlington, from NASA’s Sea Level Change team, said the findings are consistent with patterns of global coastal flooding, underscoring the complex risks posed by rising sea levels and changing climate conditions.

Hamlington told NASA that countries with limited resources face the greatest risks, highlighting the importance of a global framework to address these challenges.