Report on climate change sees grim outlook for region.
Extreme rainfall, severe droughts and wildfires could hit Auckland in years to come, according to a Niwa study on the impact of climate change on the region.
The report said the climate over the Auckland region would get hotter and the weather more volatile over the next century.
If global emissions continued on their present path, Auckland would have 70 more days over 25C each year — meaning a quarter of the year would have temperatures above this.
Average temperatures would also increase by up to 3.75C by 2110.
Head of strategy and planning at Auckland Emergency Management Craig Glover said: "The action to reduce the effects of climate change on Auckland must continue and must indeed be ramped up."
The 350-page report was commissioned by Auckland Council, Auckland Transport, Watercare and Panuku Development Auckland.
The uncertainty about the level of greenhouses gases was dealt with through consideration of "scenarios" that described concentration of gases.
A "mid-range scenario" looked at what would happen if emissions were to stabilise, while a "business-as-usual scenario" saw emissions continue unabated.
Alarmingly, the report outlined changes to weather patterns including severe droughts and extreme rain that could affect water quality and supply. While total annual rainfall would stay about the same, its seasonal distribution was projected to change markedly. It was likely rainfall in spring would decline and autumn rainfall would increase.
With the same amount of rain over a shorter time, the intensity and frequency of extreme flooding events was likely to increase. There were concerns about how this might affect water quality, as flooding into water supplies can lead to contamination.
Linked to these changes in the weather was a predicted rising sea level as well as an increased risk of wildfires.
Sea level rises were a "major concern" for Auckland as residents and infrastructure sat close to the coast, the report said.
Depending on the climate change scenario 0.5m of sea level rise was predicted between 2060 and 2110 and 1m after 2100 and after 2200.
Various communities and areas around Auckland were already feeling the impact of this.
Auckland Transport has plans to address flooding at low spots on Tamaki Drive, including raising the road by up to half a metre and adding a curve to the edge of the seawall.
The report projected an increase in the number of very high and extreme forest fire danger days, with a 50-100 per cent increase expected for areas north of Auckland's centre and a 40-50 per cent increase projected south of the isthmus by 2100.