From The Gambia to the U.S., sea saltwater incursion is increasingly seeping into the freshwaters people need for drinking and producing food. Someone turns on the tap for drinking water in New Orleans, but the water is salty. In Bangladesh, farmers are forced to turn previously fertile land into brackish ponds to raise shrimp. In The Gambia, a farmer watches her crops wither and fail, doused in salt.
Around the world, previously reliable coastal freshwater supplies are turning to salt, invaded by seawater. This is the strange, slow-moving crisis of saltwater intrusion, and it is increasingly affecting communities around the world. Saltwater intrusion refers to the inland movement of saline water – from the ocean or sea – into freshwater aquifers. It is impacting low-lying countries like The Gambia, Vietnam and Bangladesh, but is a global problem, including for the US. All continents except Antarctica are projected to have coastal areas with at least 1km (0.6 miles) of inland saltwater intrusion by 2050.
This encroaching saltwater tends to occur gradually over an extended period but presents a long-term devastating impact on drinking water sources, rice farming and coastal communities around the world, says Robert Young, a professor of coastal geology at Western Carolina University in the US. “Saltwater intrusion is a perfect example of a slow-onset climate crisis,” he says. “Too often, we focus on big events like storms, and don’t pay attention to other changes happening more slowly. We prepare for the wrong disasters, but slow-onset climate effects are the ones that can really impact the future of coastal communities, especially in the developing world.
In the US, saltwater intrusion is already present in many coastal aquifers, and is threatening farms and drinking water supply, especially in low-lying south Florida, where the vulnerable Biscayne Aquifer is the primary source of freshwater. Scientists have found wells in Rhode Island to be contaminated by saltwater. Residents of Louisiana have even begun to notice a salty taste in their tap water and, in 2023, the Louisiana state governor requested a presidential emergency declaration due to its impacts.
Saltwater intrusion into drinking water is not just unpleasant. Studies have found that populations drinking saline water are at greater risk of adverse health outcomes, including high blood pressure and health issues in pregnancy.
The intrusion often happens at the boundary or interface between saltwater and freshwater. The position of the salt depends on the balance between sea level and the water levels on land, says Holly Michael, a coastal hydrogeologist at the University of Delaware in the US. “Any process that tips that balance one way or the other is going to cause that salt front to move inland,” she says. This process is being worsened by climate change leading to rising temperatures, decreases in rainfall and a global increase in sea levels, says Michael. In some places, including the US, the excessive extraction of groundwater for demands such as domestic, agricultural and industrial has also contributed significantly to saltwater intrusion, letting underground saltwater intrude into soil and rivers.
As climate change intensifies and population increase continues to exert pressure on freshwater aquifers, the salinity crisis will only increase. By 2100, nearly 77% of the global coast will be affected by salinity, a 2024 study found. The livelihoods of many farmers will increasingly hang in the balance.
I have said, in previous blogs, that I think World War III will be fought over water. There is a multitude of evidence that drinking water, in most parts of the world, is a diminishing resource as a result of population growth and agriculture. I have previously cited Fred Pearce’s book “When the Rivers Run Dry” as a comprehensive documentation of this problem that virtually no-one is addressing; he even cites the “Range Wars” over water in the western United States as a current example of this problem, which is worldwide. I had not thought of the problem of saltwater incursion before I read this article. That only exacerbates the worldwide drinking water problem.
WE CAN LIVE WITHOUT OIL, ELECTRICITY AND MANY OTHER THINGS WE THINK ARE ESSENTIAL, BUT WE CANNOT LIVE WITHOUT DRINKING WATER AND NOR CAN ALL OTHER CREATURES ON THIS PLANET!
