Study: More Freshwater Will Be Victim of Climate Change

As sea levels rise, coastal communities could lose up to 50 percent more of their fresh water supplies than previously thought, according to a study from Ohio State University.

Scientists previously assumed that, as saltwater moved inland, it would penetrate underground only as far as it did above ground. However, Ohio State researchers suggest that when saltwater and freshwater 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. 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.

"Most people are probably aware of the damage that rising sea levels can do above ground but not underground, which is where the freshwater is," said Motomu Ibaraki, associate professor of earth sciences at Ohio State who led the study.. "Climate change is already diminishing freshwater 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."

Ohio State hydrologists simulated how saltwater will intrude into freshwater aquifers, given the sea level rise predicted by the Intergovernmental Panel on Climate Change (IPCC). The IPCC has concluded that within the next 100 years, sea level could rise as much as 23 inches, flooding coasts worldwide.

One finding of this study is that saltwater will penetrate further into areas that have a complex underground structure. Typically, coastlines are made of different sandy layers that have built up over time, Ibaraki explained. Some layers may contain coarse sand and others fine sand. Fine sand tends to block more water, while coarse sand lets more flow through.

The researchers simulated coastlines made entirely of coarse or fine sand and different textures in between. They also simulated more realistic, layered underground structures. The simulation showed that, the more layers a coastline has, the more the saltwater and freshwater mix, the researcher said. The mixing causes convection -- similar to the currents that stir water in the open sea. Between the incoming saltwater and the inland freshwater, a pool of brackish water forms.

Further sea level rise increases the mixing even more, and depending on how the various factors interact, underground brackish water can extend 10 percent to 50 percent further inland than the saltwater on the surface.

Motomu Ibaraki, associate professor of earth sciences at Ohio State, led the study. Graduate student Jun Mizuno presented the results on Oct. 30 at the Geological Society of America meeting in Denver.

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