Many low-lying atoll islands could be uninhabitable by mid-21st century

April 25, 2018, United States Geological Survey
Wave-driven flooding and overwash on Roi-Namur Atoll, Republic of the Marshall Islands. Credit: Peter Swarzenski, US Geological Survey

Sea-level rise and wave-driven flooding will negatively impact freshwater resources on many low-lying atoll islands in such a way that many could be uninhabitable in just a few decades. According to a new study published in Science Advances, scientists found that such flooding not only will impact terrestrial infrastructure and habitats, but, more importantly, it will also make the limited freshwater resources non-potable and, therefore, directly threaten the sustainability of human populations.

Most of the world's atolls are in the Pacific and Indian oceans. The scientists focused on Roi-Namur Island on Kwajalein Atoll in the Republic of the Marshall Islands for their site study from November 2013 to May 2015. The Republic of the Marshall Islands has more than 1,100 low-lying on 29 atolls, is home for numerous island nations and hundreds of thousands of people.

Scientists from the U.S. Geological Survey, Deltares, National Oceanic and Atmospheric Administration, and the University of Hawai?i at Mānoa used a variety of climate-change scenarios to project the impact of sea-level rise and wave-driven flooding on atoll infrastructure and freshwater availability. The approach and findings in this study can serve as a proxy for atolls around the world, most of which have a similar morphology and structure, including, on average, even lower land elevations.

"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," said Curt Storlazzi, USGS geologist and lead author of the new report.

Wave-driven flooding and overwash on Roi-Namur Atoll, Republic of the Marshall Islands. Credit: Peter Swarzenski, US Geological Survey

Sea levels are rising, with the highest rates in the tropics, where thousands of low-lying coral atoll islands are located. Previous studies on the resilience of these islands to sea-level rise projected they will experience minimal inundation impacts until at least the end of the 21st century. However, those previous studies did not take into account the additional hazard of wave-driven overwash (storm waters and waves that wash up and over the low-lying island) nor its impact on freshwater availability.

"Such information is key to assess multiple hazards and prioritize efforts to reduce risk and increase the resiliency of atoll islands' communities around the globe," said Storlazzi.

These findings have relevance not only to populated atoll islands in the Marshall Islands, but also to those in the Caroline Islands, Cook Islands, Gilbert Islands, Line Islands, Society Islands, Spratly Islands, Maldives, Seychelles, and Northwestern Hawaiian Islands.

Aerial photograph of Kwajalein Atoll showing its low-lying islands and coral reefs. Credit: Thomas Reiss, US Geological Survey

Thus, the study scientists project that, based on current global rates, the interactions between and wave dynamics over coral reefs will lead to an annual wave-driven overwash of most atoll islands by the mid-21st century. Such annual flooding would result in the islands becoming uninhabitable due to frequent damage to infrastructure and the inability of their to recover between overwash events.

The primary source of freshwater for populated atoll islands is rain that soaks into the ground and remains there as a layer of fresh groundwater that floats on top of denser saltwater. As atoll islands come to be overwashed annually, on average, in the next few decades (assuming current greenhouse gas emission rates), flooding impacts to infrastructure and the loss of freshwater resources would make human habitation difficult in most locations beginning between the 2030s to 2060s, requiring the relocation of island inhabitants or significant financial investments in new infrastructure.

"The overwash events generally result in salty ocean water seeping into the ground and contaminating the freshwater aquifer. Rainfall later in the year is not enough to flush out the saltwater and refresh the island's water supply before the next year's storms arrive repeating the overwash events," explained Stephen Gingerich, USGS hydrologist and co-author of the new report.

Explore further: Radiation levels on Bikini Atoll found to exceed safety standard

More information: C.D. Storlazzi el al., "Most atolls will be uninhabitable by the mid-21st century because of sea-level rise exacerbating wave-driven flooding," Science Advances (2018). DOI: 10.1126/sciadv.aap9741 , http://advances.sciencemag.org/content/4/4/eaap9741

Related Stories

Scientists counter threat of flooding on coral reef coasts

November 23, 2017

Scientists have developed a computer simulation tool to predict short-term flood hazards on coral-reef-lined coasts and to assess longer-term impacts from climate change. The assessments will give input to estimate societal ...

Recommended for you

Evidence of earliest life on Earth disputed

October 17, 2018

When Australian scientists presented evidence in 2016 of life on Earth 3.7 billon years ago—pushing the record back 220 million years—it was a big deal, influencing even the search for life on Mars.

Arctic greening thaws permafrost, boosts runoff

October 17, 2018

A new collaborative study has investigated Arctic shrub-snow interactions to obtain a better understanding of the far north's tundra and vast permafrost system. Incorporating extensive in situ observations, Los Alamos National ...

Arctic ice sets speed limit for major ocean current

October 17, 2018

The Beaufort Gyre is an enormous, 600-mile-wide pool of swirling cold, fresh water in the Arctic Ocean, just north of Alaska and Canada. In the winter, this current is covered by a thick cap of ice. Each summer, as the ice ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

24volts
not rated yet Apr 25, 2018
There might be 100's of thousands living on those islands now but in a 100 years from now those islands are just going to be hazards in shipping lanes.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.