Saltwater May Contaminate 75% of Coastal Water by 2100

Rising sea levels are wreaking havoc on coastal communities—but we should also be concerned about what’s happening beneath our gaze, as provocative new research suggests.

A new study from NASA’s Jet Propulsion Laboratory (JPL) and the US Department of Defense (DOD) suggests that seawater will contaminate fresh groundwater in about 75 percent of the world’s coastal areas by the end of this century. Their findings, published late last month Geophysical Research Lettershighlight how rising sea levels and decreasing rainfall contribute to salt water intrusion.

Fresh ground water and salty sea water maintain a unique balance under the sea. The balance is maintained by the pressure of the sea inland and the rain, which fills the aquifers (underground layers that store water). Although there is an overlap between fresh water and salt water in what is known as the transition zone, the balance usually keeps the denser water on its side.

Climate change, however, presents an opportunity for salt water in the form of two environmental changes: rising sea levels, and decreasing precipitation caused by global warming. Less rainfall means that aquifers are not fully replenished, which weakens their ability to combat the advance of saltwater, called saltwater intrusion, that comes with rising sea levels.

Saltwater intrusion is exactly what it sounds like: when saltwater enters a country in excess of what was expected, it often threatens fresh water supplies such as groundwater.

To study the future reach of saltwater intrusion, JPL and DOD researchers analyzed how rising sea levels and reduced groundwater recharge would affect 60,000 coastal watersheds (areas that drain water from features such as rivers and streams to similar bodies of water) around the world. at 2100. .

As detailed in the study, the researchers concluded that by the end of the century, 77% of the coastal water bodies studied will be affected by salt water intrusion due to the two factors mentioned above. That’s more than three out of four coastal counties surveyed.

The researchers also considered each factor individually. For example, sea level rise alone will move saltwater inland to 82% of the coastal areas considered in the study, essentially pushing the saltwater transition zone back as much as 656 feet (200 meters) by 2100. Low-lying areas such as southeast Asia, the coast of the Gulf of Mexico, and parts of the east coast of the US are especially vulnerable to this condition.

On the other hand, gradual recharge of fresh ground water would allow saltwater intrusion in only 45% of the surveyed watersheds, but would push the transition zone inland to three-quarters of a mile (about 1,200 meters). Areas including the Arabian Peninsula, Western Australia, and Mexico’s Baja California peninsula will be vulnerable to this event. However, the researchers also noted that groundwater recharge will actually increase in 42% of the remaining coastal areas, in some cases even overcoming saltwater intrusion.

“Depending on where you are and who’s in charge, your management implications may change,” said Kyra Adams of JPL and co-author of the study in a JPL statement, referring to rising sea levels and weakened aquifers.

Sea level rise will likely affect global salinity intrusion, while groundwater saturation will reflect the depth of local salinity intrusion. These two factors, however, are closely related.

“With salt water intrusion, we see that sea-level rise raises the fundamental risk of changing groundwater recharge to become a critical factor,” said JPL’s Ben Hamlington, who also led the study.

Global climate methods that take into account the impact of local climate, such as this study, are important for countries that do not have enough resources to conduct such research independently, the team highlighted, and “those with few resources are the most affected.” with sea level rise and climate change,” added Hamlington.

The end of the century may seem like a long way off, but if nations and industries need to come together to respond to these predictions, 2100 will be upon us sooner than we think.