Atolls: Uninhabitable in 15 years?

Millions of islanders could lose their homes earlier than previously thought

View over the Kwajalein Atoll in the South Pacific. These and many other islands could become uninhabitable by 2030. © Thomas Reiss / US Geological Survey
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Acute danger: The inhabitants of thousands of islands in the Pacific and Indian Ocean could become homeless earlier than previously thought. Because even before the middle of this century, a large part of these islands will be uninhabitable, as climate researchers have determined. The reason: with rising sea levels, tidal waves and floods multiply - and these saline the drinking water resources of the atolls, according to the scientists in the journal "Science Advances".

The danger is not new: the inhabitants of many coastal areas and islands have been fighting against the ever-approaching sea for years - even islands off the US east coast are in acute danger. Much harder, however, it hits the atolls and shallow islands in the tropical seas: there, the sea level rises more than on a global average, at the same time many of these islands protrude less than two meters above the ocean.

For how much longer?

How long the inhabitants of these islands remain until they have to leave their homeland, was previously in dispute. While forecasts based on sea-level rise predict a "land under" only for the end of this century, expect other researchers around 2050 with a serious lack of drinking water due to increasingly sparse rainfall on many islands.

Another bad news for residents of the tropical islands is now brought by Curt Storlazzi of the US Geological Survey and his colleagues. They have investigated a previously neglected risk factor for their study: the threat to floodplain drinking water reserves and repeated flooding. Because of the rising levels, even such events become significantly more frequent, as the researchers explain.

When the freshwater lens is salting

The problem: the drinking water of most atolls and tropical islands comes solely from rain-fed water resources. These form in the underground thin fresh water lenses, which float because of their lower density on the salty groundwater of the atolls. However, if saltwater is flushed from above into these freshwater resources during a flood, the water mixes and the drinking water becomes salted. display

Flood-related flooding on the Roi Namur atoll in the South Pacific Peter Swarzenski / US Geological Survey

The researchers have used the example of the Marshall Islands in the South Pacific to examine how acute this danger is for the thousands of tropical islands. They determined for one of the islands in the Kwajalein Atoll, as was often the case during the period from November 2013 to May 2015, and how this affected the drinking water resources. Using two models, they then calculated how this trend will continue in the future.

Uninhabitable until 2030?

The result: many atolls could become uninhabitable even before the middle of this century due to a lack of drinking water much earlier than previously thought. "The tipping point, from which potable water is no longer available, will be reached in the very near future even within the lifetime of today's islanders, " the researchers said. According to their forecasts, many islands could reach this point by 2030 to 2040, with unchecked climate change.

The reason for this: Due to rising water levels and increased floods, the flooding of the islands will occur so frequently that even heavy, repeated rainfalls can no longer flush out the salt water. "The rainfall is then no longer enough to replenish the water resources of the islands before the next year's storms and renewed flooding begin, " explains co-author Stephen Gingerich from the USGS.

Affected millions of islanders

But that means: In a few years to decades, millions of islanders could lose their homes. "Our results are valid not only for the inhabited atolls of the Marshall Islands, but also for the Carolines, the Cook Islands, the Maldives, parts of the Seychelles and also the Hawaiian Islands, " said Storlazzi and his colleagues Colleagues. "Most of these islands have a similar structure and morphology to the Kwajalein Atoll."

In addition, according to the researchers, their models may even have underestimated the danger. For example, the Marshall Islands they have chosen belong to the more elevated islands in the Pacific. Many other atolls, however, rise less far above the ocean and could therefore be salted even faster and become uninhabitable. "The timing presented here for the tipping points could therefore be too conservative, " the scientists say.

Many only escape

According to the scientists, their findings highlight the immediate threat that climate change poses to many island states and atolls. "Our data demonstrates the relevance of the threat and highlights the urgency of planning and action, " say Storlazzi and his colleagues.

Because if nothing is done, many islanders only escape from their homeland. "And that could have significant geopolitical consequences, " the researchers said. The problem: although technical solutions such as protective boots could protect many islands from increased flooding. But most of these measures are simply too expensive for the island states. Without the help of the industrialized countries - for example through a relief fund as decided in the Paris Climate Agreement - it will hardly be possible. (Science Advances, 2018; doi: 10.1126 / sciadv.aap9741)

(US Geological Survey, 26.04.2018 - NPO)