According to the Jet Propulsion Laboratory (JPL) in California, seawater will infiltrate underground freshwater supplies in about three of every four coastal areas around the world by the end of this century, barely seventy-five years in the future.
Saltwater moves under coastlines where two masses of water naturally hold each other at bay and something changes this balance. Rainfall on land replenishes, or recharges, fresh water in coastal aquifers, and flow below ground toward an ocean or bay. Coastal seawater, affected by the pressure of the ocean pushes inland against this groundwater. Mixing occurs in marshy transition zones but the balance of opposing forces typically keeps the water fresh on one side with the seawater on the other. Now, the impacts of climate change are tipping the scales in favor of the saline water.
This process is being altered by a warmer atmosphere that is impacting ice sheets on Greenland. Between 2002 and 2023 it has been estimated that Greenland lost 270 gigatons of ice/year causing the sea level to rise by 0.03 inches/year. This rising water is pushing coastlines to change their shape with the force of salt water increasingly pushing inland. Additionally, slower groundwater recharge from less rainfall and drier weather conditions is weakening the force of the fresh water in the underground aquifers.
A new study, published by Geophysical Research Letters, investigated 60,000 coastal watersheds around the world and mapped how the diminished groundwater recharge and the rise in sea level will contribute to saltwater intrusion and estimated what the net effect will be. The JPL researchers found that by the year 2100 rising sea levels will drive saltwater inland in 82% of the coastal zones studied. One of the lead authors noted that:
As sea levels rise, there is an increased risk of flooding everywhere. With saltwater intrusion, we’re seeing that sea level rise is raising the baseline risk for changes in groundwater recharge to be a serious factor.
Their map illustrates the global extent of the new findings.
Saltwater intrusion of coastal zones by 2100 (credit: Geophysical Research Letters)
The year 2100 is still years away but some coastal zones are already experiencing damaging saltwater intrusion today, especially along regions of the Gulf of Mexico in Louisiana, Mississippi, and Texas. Efforts to halt the advance of an underwater wall of saltwater in the Mississippi River seems an expensive 'whistling in the wind' attempt. Reducing greenhouse gas emissions, which are causing the atmospheric heating that is driving ice melting, would be a better long-range approach. WHB