Coastal groundwater is an important source of freshwater for communities living near the ocean. However, rising sea levels, stronger storms, and excessive groundwater pumping allow saltwater to seep into these aquifers, making the water too salty to drink or use for farming. Predicting when this harmful change will occur is challenging because groundwater systems respond slowly to environmental stress.

This study looks for early signs that a coastal groundwater system is becoming unstable. To do this, daily measurements of water quality, particularly the amount of dissolved salts (measured as electrical conductivity), were analyzed over many years. By looking at patterns in these data, such as increasing variability or slower recovery after disturbances, it is possible to see warning signs that the groundwater is approaching a critical tipping point.

The results show that certain patterns in the data consistently appear before large increases in salt levels occur. This new approach can help water managers detect risks sooner and take action to protect freshwater supplies, for example by reducing pumping or planning alternative water sources. The method offers a tool for communities to better adapt to climate change and protect their coastal resources.