A team of scientists projects that many of the low-lying atoll islands will be uninhabitable by mid-21st century due to rising of sea levels resulting from climate change.

Experts from the U.S. Geological Survey, Deltares, the National Oceanic and Atmospheric Administration and the University of Hawaiʻi at Mānoa note that sea-level rising and wave-driven flooding will lead to scarcity of the freshwater resources among the chain of islands in the Pacific and Indian Oceans. The extent of the damage will make the areas squalid and hostile toward human population by mid-2030s to 2060s.

The projection was based on the observed "overwash," which is happening yearly due to the combination of greenhouse gas emissions, sea-level rising, and storms waves over coral reefs. Overwash is the amount of seawater and sediment deposited on sand dunes after storms and flooding.

Overwash accumulating each year will also damage the infrastructure on these islands, making it much harder for potable water resources to recover from storm events.

Overwash and Potable Water

The rain is the major source of groundwater on the atoll islands. When rain pours, the water penetrates the ground and it remains in there, afloat over saltwater.

Groundwater flows through an aquifer or the permeable layer of soil, sand, silt, and rocks. After freshwater enters aquifer, it flows through the springs, streams, or wells where humans can acquire them.

When there is overwash, salty water seeps into the aquifer layer, contaminating the freshwater that could have streamed through the aquifer.

Naturally, this saltwater deposit should be flushed out by rainwater. However, due to climate change, the amount of seasonal rainfall becomes insufficient to flush out the salty water deposits.

The overwash will then reside and will continue to accumulate every time stronger storms arrive, says Stephen Gingerich, USGS hydrologist. If this persists, it will reach a point where saltwater will overcome freshwater.

"The tipping point when potable groundwater on the majority of atoll islands will be unavailable is projected to be reached no later than the middle of the 21st century," highlights Curt Storlazzi, USGS geologist and lead author of the report published in Science Advances.

Uninhabitable Islands

The focus of the study is the Roi-Namur Island on Kwajalein Atoll. It is located in the Republic of the Marshall Islands, which has 1,100 low lying islands on 29 atolls.

While the study has only focused on this location, the experts highlight that their finding could reflect similar situation happening on other habited atoll islands. Potable water resources may soon be a problem on people living in the Caroline Islands, Cook Islands, Gilbert Islands, Line Islands, Society Islands, Spratly Islands, Maldives, Seychelles, and Northwestern Hawaiian Islands.

The experts add that their findings can also be applied for atolls located anywhere the globe because most of the atoll islands have the same morphology and structure. Ultimately, the information contained in their study will be significant in increasing the resiliency of communities across all atoll islands.

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