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Sea level rise reveals actual risk

National Institute for Water and Atmospheric Research [Niwa] and Deep South National Science Challenge have created maps showing the areas across Aotearoa that could be inundated by extreme coastal flooding, painting a worrying picture for some of Wairarapa.

The maps show what could happen when there is a large storm tide combined with different sea level rise scenarios that are anticipated as a result of climate change.

The map and data add to the information already available from regional councils.

Dr Scott Stephens, Niwa’s chief scientist for coasts and estuaries, said the research has found that small amounts of sea-level rise could drive a rapid increase in cumulative flooding from increasingly frequent coastal flood events, and 30 per cent more land area would be regularly flooded after 0.3m relative sea-level rise.

Stephens said coastal flooding is particularly likely when high tides, storm surges, and large waves occur simultaneously.

At these times, low-lying areas are inundated when high seas go over the top, or even break barriers and cause rivers to back up inland.

“By 2065, there could be 0.4m of sea-level rise, based on the current trajectory, or sooner where the landmass is subsiding,” Stephens said.

At 0.4m of sea level rise, land surrounding local rivers and Lake Wairarapa could be subject to extreme coastal flooding, according to the map.

In the worst-case scenario, with 2m of sea level rise, flooding from a storm surge could reach as far as, and cover, Kahurara Rd in Featherston.

Other parts of the Wellington region, including Lower Hutt, could see similar effects with 0.4m of sea level rise. Under the scenario, extreme coastal inundation could see flooding almost reach the base of the Wainuiomata Hill Rd.

Stephens said that the maps would help shape decisions on how sea-level rise is adapted to.

“Coastal flooding is a global hazard that impacts New Zealand, with rising sea levels already causing more frequent and intense flooding along many coasts. We have created maps that help identify the changing risk to land, property, and infrastructure from rising seas.”

Stephens said coastal flooding could destroy property and infrastructure, and be a danger to life, as well as have severe impacts on the natural environment and ecosystems.

“With much of our major infrastructure and roughly 65 per cent of New Zealanders living within 5km of the coast, this is an issue that will impact many of us, so we must be aware of what’s coming and be prepared to adapt.

“These maps are not designed for assessing exposure to individual properties, however. Many councils have more detailed maps for that purpose,” Stephens said.

“The advantage is that they fill in gaps for areas of the country that don’t currently have this data available, they provide nationwide information, and they include many scenarios of sea-level rise.”

The map was used in new research that examined New Zealand’s increasing exposure to coastal flooding.

Stephens said Niwa hopes the information contained in the map will raise awareness and help councils and government to know where to conduct detailed investigations when developing adaptation strategies to protect coastal communities.

He said the maps are also intended to help the financial industry, national infrastructure, and service providers to risk assess their portfolios.

“It’s difficult to make decisions about the future if you can’t see it – these maps provide a window into the future.”

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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