Climate change could diminish drinking water more than expected

Terra Daily: As sea levels rise, coastal communities could lose up to 50 percent more of their fresh water supplies than previously thought, according to a new study from Ohio State University. Hydrologists here have simulated how saltwater will intrude into fresh water 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.

Scientists previously assumed that, as saltwater moved inland, it would penetrate underground only as far as it did above ground. But this 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.

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. Motomu Ibaraki, associate professor of earth sciences at Ohio State, led the study. Graduate student Jun Mizuno presented the results Tuesday, October 30, 2007, at the Geological Society of America meeting in Denver.

"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."

In the United States, lands along the East Coast and the Gulf of Mexico -- especially Florida and Louisiana -- are most likely to be flooded as sea levels rise. Vulnerable areas worldwide include Southeast Asia, the Middle East, and northern Europe….

Scientists have used the IPCC reports to draw maps of how the world's coastlines will change as waters rise, and they have produced some of the most striking images of the potential consequences of climate change. Ibaraki said that he would like to create similar maps that show how the water supply could be affected.

..."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." One way to create more fresh water is to desalinate saltwater, but that's expensive to do, he said. "To desalinate, we need energy, so our water problem would become an energy problem in the future."