The Southland District Council needs to get a better handle on understanding the effects of climate change before it can make sound decisions and recommendations in the future, chief executive Cameron McIntosh says.
The council was last week considering a report prepared by Great South on the impact climate change would have on the district.
Six townships were modelled: Fortrose, Colac Bay, Riverton, Curio Bay, Waikawa and Oban.
Climate change-induced sea level rise was a dynamic and changing area of science and there still had to be an agreed rate of climate change.
The report outlined sea level rises and extreme sea level exposure based on spatial modelling and the 8.5 climate change scenario, which was the worst case scenario. While there were five change scenarios, the Ministry of the Environment recommended the 8.5 model be used in the interim.
"Until we have alternative guidance, we won’t be deviating from that particular path."
A methodology disclosure also stated the longer the modelling period the greater the uncertainty.
"Long-term modelling was fraught with a major range of vagaries, however short-term modelling should be closer to what will eventuate."
Cr Jaspreet Bopari challenged the presented data because it had opted to use the "hyped-up scenario SSP 8.5".
The Intergovernmental Panel on Climate Change (IPCC) had claimed the 8.5 scenario was implausible and should only be used as a stress test, she said
"Our policies are not to be based on a scenario that IPCC itself declares as implausible and not likely to unfold. I can tell you the ramifications, the repercussions for our ratepayers will be very much real."
Some things were clearly being affected by coastal inundation because it could be seen.
"We must be extremely, extremely careful about not causing our ratepayers very tangible harm by using improbable forecasts."
Mr Canny said he believed it was more prudent to focus on the scenario outlining the next 70 years rather than the worst case scenario which predicted a 4.95m sea level rise around the Southland coastline by 2300.
Mr McIntosh said, in a statement about the report, communities were already experiencing the effects of sea level rise and changing weather.
The council has commissioned this work to provide a basis for better future decision making.
“Council has a responsibility to identify natural hazards, including those that will result from the effects of climate change in the future, and do our best to draw on this information in short, medium and long-term decision-making," he said.
Vertical land movement around the coast presented a more real scenario. "Essentially the whole Southland coast is either rising or falling."
Curio Bay’s terrain declined by 3mm a year while Oban’s lifted 1.6mm-2.77mm a year.
While Oban’s land was rising, it was not outpacing sea level increases.
The biggest threat to Southland’s coastal community came from storm surge wave ramp-up.
While the sea inundation events would more likely be a 1 in 100-year scenario, over time the frequencies would increase.
Storm events would likely inundate all of the coastal communities in the study.
Riverton had a significant risk where modelling predicted the township would be inundated.
"We would all hope that isn’t the case, but we need to be aware is a potential for that area."
Sea level increases would be felt by Waikawa, Curio Bay and Fortrose by 2090.
The final report was to be completed, peer reviewed and presented by November 17.
- By Toni McDonald
