The findings are based on the report of the Intergovernmental Panel on Climate Change (IPCC) which has concluded that sea level could rise as much as 23 inches within the next 100 years, thus flooding coasts worldwide. In the United States, lands along the East Coast and the Gulf of Mexico are most likely to be flooded as sea levels rise. Vulnerable areas worldwide include Southeast Asia, the Middle East, and northern Europe.
Based on this report, hydrologists have simulated how this situation would lead to saltwater intruding into fresh water aquifers. The researchers simulated coastlines made entirely of coarse or fine sand, and different textures in between.
Scientists had previously assumed that, as saltwater moved inland, it would penetrate underground only as far as it did above ground.
According to Motomu Ibaraki, associate professor of earth sciences at Ohio State, "Most people are probably aware of the damage that rising sea levels can do above ground, but not underground, which is where the fresh water is."
The new research shows that when saltwater and fresh water meet, they mix in complex ways, depending on the texture of the sand along the coastline. In some cases, a zone of mixed, or brackish, water can extend 50 percent further inland underground than it does above ground.
This was also illustrated in the simulations made by the scientists. It showed that, the more layers a coastline has, the more the saltwater and fresh water mix. The mixing causes convection, which is similar to the currents that stir water in the open sea. Between the incoming saltwater and the inland fresh water, a pool of brackish water forms.
Further sea level rise increases the mixing even more, which leads to the underground brackish water being extended 10 to 50 per cent further inland than the saltwater on the surface.
Like saltwater, brackish water is not safe to drink because it causes dehydration. Water that contains less than 250 milligrams of salt per liter is considered fresh water and safe to drink.
"Climate change is already diminishing fresh water resources, with changes in precipitation patterns and the melting of glaciers. With this work, we are pointing out another way that climate change can potentially reduce available drinking water. The coastlines that are vulnerable include some of the most densely populated regions of the world," Ibaraki added.
"Almost 40 percent of the world population lives in coastal areas, less than 60 kilometers from the shoreline," Mizuno said. "These regions may face loss of freshwater resources more than we originally thought," he added.
The solution for this crisis situation is obtaining economical water for everybody.
"In order to obtain cheap water for everybody, we need to use groundwater, river water, or lake water," Ibaraki said.
But the problem is that these water resources are disappearing due to several factors like an increase in demand and climate change. This calls for the need to create new fresh water resources.
"One way to create more fresh water is to desalinate saltwater, for which we need massive energy," said Ibaraki. "So our water problem would become an energy problem in the future," he added.