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Sea level rise a double whammy

Parts of the Wairarapa coast are losing up to 6mm of land to the sea each year, due to some of the highest rates of sea level rise in New Zealand.

Greater Wellington Regional Council [GWRC] scientist Dr Iain Dawe, Professor Tim Naish of Victoria University, and Dr Richard Levy from GNS Science presented their findings to the Climate Committee on Thursday.

The scientists said while climate change and warming temperatures were causing sea levels to rise, on average, by 3.5mm per year, some Wairarapa areas were experiencing more than double this when land sliding into the sea was taken into account.

Dawe said data collected over the past 20 years shows the Wellington Region has a “tectonic subsidence” of -1 to 4mm per year, which results in a doubling of the rate of average sea level rise caused by climate change.

The scientists said this sea level rise was caused by the thermal expansion of the ocean, by melting glaciers, and by melting of the Greenland and Antarctic ice sheets.

The effects of the sea level rise could be dire, with increased coastal flooding and potential permanent inundation of estuaries, coastal wetlands, and river mouths.

The report said the higher the sea level becomes the more exposed the coast will be to storm damage.

Additionally, salt water could begin to enter rivers and aquifers. Beaches will also erode, and the shoreline may change entirely.

Sea level rise is now locked in and has reached a point of no return, the researchers said.

Naish said councils and communities needed to begin planning to experience 50cm of sea level rise by 2100 and between 20 to 30cm by the middle of the century – all before factoring in vertical land movement.

“Once you add in vertical land movement, you essentially half the time you have until you get to 50cm.”

“Even if you take the best-case scenario for future sea level rise, that has a significant impact on how soon you’ll be dealing with thresholds whereby infrastructure is no longer usable, and communities are getting inundated regularly,” Niash said.

Current flood protection systems are designed to cope with an extreme once-in-a-century event, Levy noted, but those weather events will soon be occurring every year, with 30cm of sea level rise seen since 2005.

He said although earthquakes on Wairarapa and Wellington faults could push land upwards or downwards, the chance of an uplift shouldn’t be relied upon to “save us” from sea level rise.

Levy said regardless of what people do to adapt to an uncertain future, there was one thing that needed to be done – cut our greenhouse gas emissions now.

“Sea level rise is here to stay.”

Grace Prior
Grace Prior
Grace Prior is a senior reporter at the Wairarapa Times-Age with a keen interest in environmental issues. Grace is the paper’s health reporter and regularly covers the rural sector, weather, Greater Wellington Regional Council, and coastal stories.

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