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Groundwater's contribution to sea-level rise overblown



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Groundwater’s contribution to sea-level rise overblown

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Groundwater extraction contributes about three times less to sea-level rise than previously estimated, according to a new study published in the journal Nature Climate Change.

Earlier studies assumed that nearly 100% of extracted groundwater and other land water ended up in the ocean.

But the new study - which improves accounting for feedbacks between the land, ocean, and atmosphere - finds that number is closer to 80%.

“During the 20th century and early 21st century, cumulative groundwater contribution to global sea level was overestimated by at least 10mm,” said IIASA Researcher Yoshihide Wada, who led the study.

Researchers have attributed the rising seas to a combination of factors including melting ice caps, glaciers thermal expansion and the extraction of groundwater for human use.

But with this study finding land water's contribution had been overestimated, other processes had likely been underestimated, Wada said.

“Projecting accurate sea-level rise is important, because rising sea level is a threat to people who live near the ocean and in small islands,” he said.

“Some low-lying areas will have more frequent flooding, and very low-lying land could be submerged completely.

This could also damage substantially coastal infrastructure.”

According the the new study, the contribution of land water to global sea level rise was actually slightly negative between 1971 to 2010, meaning that more water was stored in groundwater and also due to reservoir impoundment behind dams.

From 1993 to 2010, the study estimated terrestrial water contributed 0.12 mm per year to sea level rise.

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Wada said the impact was a lot broader.

“The water stored in the ground can be compared to money in the bank. If you withdraw money at a faster rate than you deposit it, you will eventually start having account-supply problems,” Wada said.

“If we use groundwater unsustainably, in the future there might not be enough groundwater to use for food production.

“Groundwater depletion can also cause severe environmental problems like reduction of water in streams and lakes, deterioration of water quality, increased pumping costs, and land subsidence.”

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