Drinking water near coasts is under threat worldwide

A recent study shows how the salinization of groundwater due to over-abstraction and rising sea levels is becoming a global problem

14 April

Coastal groundwater is a key source of drinking water in many regions of the world. However, it is threatened by over-abstraction and the potential for salinization. Rising sea levels are further exacerbating the situation. This is demonstrated by a recent study published in Nature Water by a research team led by Professor Robert Reinecke from the Institute of Geography at Johannes Gutenberg University Mainz (JGU) and Annika Nolte from the Climate Service Center Germany (GERICS) in Hamburg. "Between 1990 and 2024, more than 20 percent of the coastal areas we studied showed significant changes in the groundwater level. In some cases, levels have dropped by more than 50 centimeters per year. This points to over-abstraction and, consequently, the potential intrusion of seawater and associated salinization," explained Professor Robert Reinecke. The interaction between over-abstraction and rising global sea levels due to global warming is particularly critical: "If groundwater levels drop, seawater can intrude more easily."

Data from about 480,000 wells

The study is based on data from approximately 480,000 wells across different countries, compiled by the researchers, making it the largest global dataset of coastal groundwater measurements to date. "Our study makes three key contributions. First, it translates available measurement data from different locations into globally comparable metrics, enabling large-scale assessment for the first time. Second, it identifies areas at particular risk and highlights the changes occurring there. Third, it provides indicators that can be used to model developments along previously unmonitored coastlines," said Reinecke.

Changes in groundwater levels in the affected areas vary considerably: levels have risen in some locations, while in others they have declined. However, since 2016, researchers have observed an overall increase in declining groundwater levels. "The extent of groundwater-level change varies significantly, even on a small scale within many regions," said Reinecke. Falling levels have been observed primarily along the coasts of the United States and Central America, the Mediterranean region, South Africa, India, and southern Australia.

The study also examined where coastal groundwater is particularly vulnerable to saltwater intrusion. "Coastal areas where the groundwater table is close to sea level are especially at risk, as are arid regions where populations rely heavily on groundwater. Our study provides global evidence that coastal groundwater is threatened by salinization and must be prioritized for monitoring and management," emphasized Reinecke. "Over the next 50 years, drinking water shortages could arise in all coastal areas of the world." This poses risks not only to the water supply of coastal populations - accounting for more than 30 percent of the world's population - but also to local food production and ecosystems.