According to a recent study led by researchers at NASA’s Jet Propulsion Laboratory in Southern California, seawater will infiltrate groundwater supplies in three out of every four coastal areas around the world by 2100. In addition to making water in some coastal watersheds undrinkable and unusable for irrigation, these changes can damage ecosystems and degrade infrastructure.
Called saltwater intrusion, this phenomenon occurs beneath coastlines, where two large bodies of water naturally keep each other at bay. Rainfall on land replenishes, or recharges, fresh water in coastal aquifers (underground rock and soil that hold water), which flow underground to the ocean. Seawater, meanwhile, pushes inward with the help of ocean pressure. Although there is some mixing in the transition zone where the two meet, the balance of opposing forces generally keeps the water fresh on one side and salty on the other.
Now, two effects of climate change are tipping the scales in favor of saltwater. Due to planetary warming, sea level rise is increasing the force of coastlines to migrate inland and push saltwater inland. At the same time, slow groundwater recharge due to low rainfall and warmer weather patterns is undermining the ability of groundwater to transport fresh water in some areas.
Interference around the world
gave studyPublished in Geophysical Research Letters in November, the study examined more than 60,000 coastal watersheds (the area of land that drains all the rain and snow from a region into a common outlet) around the world, mapping out how groundwater How will decreasing recharge and sea level rise occur? Contribute to saltwater intrusion by estimating what their net effect will be.
Considering the two factors separately, the study’s authors found that sea-level rise alone would tend to drive saltwater inland into 82 percent of coastal aquifers by 2100. The transition zone at these locations would be a relatively small distance: no more than 656 feet (200 m) from existing positions. Vulnerable areas include low-lying areas such as Southeast Asia, the coast around the Gulf of Mexico, and the eastern seaboard of the United States.
Meanwhile, slow recharge on its own would cause saltwater intrusion into 45% of coastal aquifers. In these areas, the transition zone would move inland much more than sea level rise—in some places three-quarters of a mile (about 1,200 meters). The most affected areas include the Arabian Peninsula, Western Australia and Mexico’s Baja California Peninsula. In about 42% of coastal watersheds, groundwater recharge will increase, tending to push the transition zone seaward and some Overcomes the effects of saltwater intrusion from sea level rise in areas.
All told, due to the combined effects of changes in sea level and groundwater recharge, 77 percent of coastal aquifers will be intruded by saline water by the end of the century, according to the study.
In general, low rates of groundwater recharge dictate how far saltwater intrudes inland, while sea level rise will determine how widespread it is globally. “Depending on where you are and who dominates, your management implications can change,” said Kyra Adams, an Earth scientist at JPL and lead author of the paper.
For example, if low recharge is the main cause of intrusion in an area, local authorities can address it by protecting groundwater resources, he said. On the other hand, if there is greater concern that sea level rise will exceed the aquifer, authorities may divert groundwater.
Global Consistency
The study, a collaboration between NASA and the US Department of Defense (DOD), is part of an effort to assess how sea-level rise will affect the Department’s coastal facilities and other infrastructure. He used information about watersheds collected in Hydrosheds, a database maintained by the World Wildlife Fund that draws on elevation observations. NASA Shuttle Radar Topography Mission. To estimate the distance of saltwater intrusion by 2100, the researchers accounted for, among other variables, groundwater recharge, water table rise, density of fresh and salt water, and coastal migration from sea level rise. A model was used.
Study author Ben Hamlington, a climate scientist at JPL and co-leader of NASA’s Sea Level Change Team, said the global picture is similar to what researchers see with coastal flooding: “As sea level rises , the risk of flooding increases everywhere. With saltwater intrusion, we see sea level rise becoming a serious factor in changes in groundwater recharge.”
A consistent global framework that captures local climate impacts is critical for countries that lack the expertise to develop one on their own, he added.
“Those with fewer resources are the most affected by sea level rise and climate change,” Hemlington said, “so this kind of approach can go a long way.”
News media contacts
Andrew Wang / Jane J. Lee
Jet Propulsion Laboratory, Pasadena, California
626-379-6874 / 818-354-0307
andrew.wang@jpl.nasa.gov / jane.j.lee@jpl.nasa.gov