Salt water may contaminate 75% of coastal freshwater by 2100

Sea level rise is causing visible damage to coastal communities, but we should also worry about what’s happening below our line of sight, alarming new research suggests.

New research by NASA’s Jet Propulsion Laboratory (JPL) and the U.S. Department of Defense (DOD) suggests that seawater will contaminate groundwater in about 75 percent of the world’s coastal areas by the end of the century. Their findings, published Late last month in Geophysical Research LettersHighlighting how rising sea levels and decreased rainfall contribute to saltwater intrusion.

Groundwater freshwater and oceanic saltwater maintain a unique balance beneath the coasts. The balance is maintained by the internal pressure of the oceans as well as rainfall, which replenishes fresh aquifers (the underground layers of the earth that store water). While there is some overlap between freshwater and saltwater in what is known as the transition zone, the balance usually keeps each body of water on its own side.

However, climate change is giving salty water an advantage in the form of two environmental changes: rising sea levels and decreasing precipitation resulting from global warming. Low rainfall means that aquifers are not fully replenished, weakening their ability to cope with the advance of salt water, called saltwater intrusion, that comes with rising sea levels.

A saltwater intrusion is exactly what it sounds like: when saltwater seeps inland farther than expected, often endangering freshwater supplies such as aquifers.

To study the future extent of saltwater intrusion, JPL and Department of Defense researchers analyzed how sea level rise and diminished groundwater replenishment would affect more than 60,000 coastal watersheds (areas that drain water from features such as rivers and streams into a common body of water) across the world. around the world by the year 2100.

As detailed in the study, the researchers concluded that by the end of the century, 77% of the coastal watersheds studied will be affected by saltwater intrusion due to the two environmental factors mentioned above. This represents more than three out of every four coastal areas assessed.

The researchers also looked at each factor separately. For example, sea level rise alone will move saltwater inland in 82% of the coastal watersheds examined in the study, specifically pushing the freshwater-saltwater transition zone back by as much as 656 feet (200 m) by 2100. Southeast Asia, the Gulf Coast of Mexico, and parts of the East Coast of the United States are particularly at risk from this phenomenon.

On the other hand, slower replenishment of groundwater freshwater would allow saltwater intrusion into only 45% of the watersheds studied, but would push the transition zone inland by up to three-quarters of a mile (about 1,200 metres). Areas including the Arabian Peninsula, Western Australia and the Baja California Peninsula in Mexico will be vulnerable to this occurrence. However, the researchers also noted that groundwater replenishment would actually increase in 42% of the remaining coastal watersheds, and in some cases would overcome saltwater intrusion.

“Depending on where you are and who dominates, your management implications may change,” said Kira Adams of JPL and co-author of the study in JPL Bulletin. statementin reference to the rise in sea levels and the weakness of groundwater aquifers.

Sea level rise is likely to influence the impact of saltwater intrusion on a global scale, while groundwater replenishment will indicate the depth of local saltwater intrusion. However, these two factors are closely linked.

“With saltwater intrusion, we see that sea level rise increases the fundamental risk of changes in groundwater recharge becoming a serious factor,” said Ben Hamlington of JPL, who also co-led the study.

The team stressed that global climate approaches that take into account local climate influence, such as this study, are essential for countries that do not have sufficient resources to conduct such research independently, and “those with the least resources are most affected.” “Because of sea level rise and climate change,” Hamlington added.

The end of the century may seem like a long way away, but if countries and industries need to mobilize in response to these predictions, the year 2100 will be upon us sooner than we think.