By 2100, saltwater could contaminate 75% of coastal freshwater
New research by NASA’s Jet Propulsion Laboratory and the U.S. Department of Defense suggests that saltwater will infiltrate underground freshwater beneath 75 percent of coastal areas around the world by the end of this century. Their findings, published late last month in Geophysical Research Letters, highlight how rising sea levels and declining rainfall contribute to saltwater intrusion.
Underground fresh water and the ocean’s saltwater maintain a unique equilibrium beneath coastlines. The ocean’s pressure inland and rainfall replenish the fresh water aquifers, underground layers of earth which store water. The lack of rain means that aquifers are not fully replenished, which makes them less able to counter the saltwater advance, also known as saltwater intrusion, that comes with rising sea levels. Less rain means aquifers aren’t fully replenished, weakening their ability to counter the saltwater advance, called saltwater intrusion, that comes with rising sea levels.
Saltwater intrusion is exactly what it sounds like: when saltwater intrudes inland further than expected, often jeopardizing freshwater supplies such as aquifers.
To study the future reach of saltwater intrusion, JPL and DOD researchers analyzed how rising sea levels and diminishing groundwater replenishment will impact over 60,000 coastal watersheds (areas that drain water from features such as rivers and streams into a common body of water) worldwide by 2100.
As detailed in the study, the researchers concluded that by the end of the century, 77% of the studied coastal watersheds will be impacted by saltwater intrusion because of the two aforementioned environmental factors. This is more than three out of four coastal regions evaluated. Rising sea levels will push saltwater inland by as much as 656 feet in some coastal watersheds. Low-lying regions such as southeast Asia, the Gulf of Mexico coast, and parts of the US east coast are especially at risk of this phenomenon.
On the other hand, a slower replenishment of underground freshwater will allow saltwater intrusion in just 45% of the studied watersheds, but will push the transition zone inland as far as three-quarters of a mile (about 1,200 meters). This will affect areas such as the Arabian Peninsula and Mexico’s Baja California Peninsula. However, the researchers also noted that groundwater replenishment will actually increase in 42% of the remaining coastal watersheds, in some cases even prevailing over saltwater intrusion.
“Depending on where you are and which one dominates, your management implications might change,” Kyra Adams of JPL and a co-writer of the study said in a JPL statement, referencing rising sea levels and weakened aquifers.
Sea level rise will likely influence the impact of saltwater intrusion on a global scale, whereas groundwater replenishment will indicate the depth of local saltwater intrusion. Both factors are closely related.
