Rising Seas Threaten Drinking Water Supplies

While scientists have already predicted that climate change and rising sea levels will affect underground supplies of fresh water for drinking, the impact could be much greater than previously expected, according to new research from Ohio State University (OSU).

Using computer simulations to see how rising oceans might encroach into freshwater aquifers on land, Motomu Ibaraki, associate professor of earth sciences at OSU, found that salt water could contaminate underground supplies up to 50 percent farther inland than it would above ground. The impact stems from a mixing of salt water and fresh water, which creates brackish water that is not appropriate for drinking.

Drinking brackish water causes dehydration because it contains too much dissolved salt. Water needs to have less than 250 milligrams of salt per liter to be considered fresh and safe for drinking.

"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," Ibaraki said. "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."

Those regions include the East Coast and Gulf of Mexico in the U.S., as well as Southeast Asia, the Middle East and northern Europe.

"Almost 40 percent of the world population lives in coastal areas, less than 60 kilometers from the shoreline," said Jun Mizuno, an OSU graduate student who helped Ibaraki conduct the research. "These regions may face loss of freshwater resources more than we originally thought."

Determining exactly how much underground fresh water might be affected by rising sea levels is complicated because of many factors. First, scientists aren't sure exactly how much fresh water is stored in underground aquifers, nor where all those aquifers might be located. Second, they don't always know details about the underground structures of coastal areas; the types of sand and layering underground affects how saltwater mixes with fresh water.

During their simulations, the OSU researchers found that underground layers of fine sand tend to block more incoming saltwater. However, saltwater seeps in further in areas with coarse sand or a greater number of underground layers. Convection between fresh water and incoming saltwater can cause pools of brackish water to form underground anywhere from 10 to 50 percent farther than the seas actually reach above ground, the researchers found.

"In order to obtain cheap water for everybody, we need to use groundwater, river water, or lake water," Ibaraki said. "But all those waters are disappearing due to several factors -- including an increase in demand and climate change."

Removing salt from seawater could provide more drinking water, but that's a costly and energy-intensive process, Ibaraki added.

"To desalinate, we need energy, so our water problem would become an energy problem in the future," he said.

Ohio State University, "Climate Change Could Diminish Drinking Water More Than Expected." URL: (http://researchnews.osu.edu/archive/saltwatr.htm)