A wet winter has resulted in more slips in Wellington and a new report warns there could be a higher risk of many more. Photo: RNZ / Craig Stephen
A new report on Wellington's changing climate forecasts increasing temperatures, strong winds and intense rain around the region.
Heavy rainfall events have been the catalyst for a major increase in slips around the region this year and with this continuing to worsen, slips could easily follow suit.
The report, Climate change projections for west of Wellington's Tararua and Remutaka Ranges, was prepared by the National Institute of Water and Atmospheric Research (NIWA) for the Greater Wellington Regional Council.
It used the most recent climate change projections based on the Intergovernmental Panel on Climate Change's five models, downscaled for the Wellington region.
NIWA climate scientist Gregor Macara, who was one of the report's authors, said the heavy rainfall events that generated slips and floods and overwhelmed storm water and wastewater systems were set to become more severe.
The report showed heavy rainfall events could increase by 16 percent by 2040, and by 30 percent by 2090.
Extreme bursts over very short durations, which were of importance for flood protection design, could increase by up to 40 percent.
Southern areas and Wellington city were likely to feel the most impact from coastal inundation, flash floods and slips, the report said.
A slip in the Wellington suburb of Brooklyn in July. Photo: RNZ / Kent Atkinson
Areas west of the Tararua and Remutaka Ranges, already a hot spot for severe weather events, will experience more storms, ex-tropical cyclones, coastal storm surges, drought and intense rainfall bursts, leading to more frequent coastal and river flooding, erosion and slips.
On the flip side, dry spells were projected to increase by up to 13 days per year in the south by mid-century. Under the high emission scenario, Wellington city and Porirua could equal Martinborough, which is among the driest spots in the Wairarapa.
Wellington's notoriously strong winds were also predicted to worsen, with the total number of windy days projected to increase by up to five days a year by mid-century and by up to 11 more days a year by the end of the century.
"With more energy in the atmosphere, with higher temperatures, that drives stronger storm events," Macara explained.
"Also, it increases the temperature difference between, say, the polar regions, so to the south of New Zealand, and the more subtropical regions. So you get a higher temperature gradient between those two, which strengthens the westerly wind."
Another report released earlier this year showed sea levels around Wellington were rising twice as fast as previously thought.
This latest report didn't address sea level rise specifically, but it remained a key consideration for the region, Macara said.
"The more we can do now to reduce our carbon emissions and reduce those greenhouse gases in the atmosphere, the less severe those future impacts of climate change will be," he said.
'We have to commit to decisive action now'
Regional council chairperson Daran Ponter said the changes would test the country's capacity and approach to flood protection, coastal erosion mitigation, protecting urban water supplies and preserving biodiversity.
"These projections should be seen as a clear warning for the region and a spur to action. It's not too late to reduce emissions," he said.
"We still have the opportunity to improve resilience and create communities that can thrive in a changing natural environment, but we have to commit to decisive action now."
The regional council has set goals to this effect: halving greenhouse gas emissions by 2030, allowing the region to reach carbon net-zero by 2050, along with a 35 percent reduction in emissions from land transport.
"Our role as a council is to take the lead in enabling people to reduce emissions and prepare for the impact of climate change," Ponter said.