Auckland Council has released documents showing just how vulnerable the region's housing is to flooding.
It warns the likelihood of "high intensity rainfall events" will increase due to climate change, and around 137,000 buildings in the Auckland region are at risk of flooding.
The research was released as part of a stormwater resource consent application, which contained plans on how to deal with increased water flow.
"Flooding is one of the most significant and frequent natural hazards in the Auckland region," the council warns.
It estimates that there are about 137,000 buildings potentially affected by flooding bad enough to happen just once a year. Around 16,000 buildings would be flooded above floor level.
"Flood risk needs to be managed and mitigated to avoid loss of human life, protect buildings and property, minimise disruption to significant infrastructure and facilities, and minimise social and economic costs," the council says.
"Climate change is likely to increase the frequency and magnitude of high intensity rainfall events, which may further exacerbate flood risk and directly impact on infrastructure and development across Auckland."
Last weekend, west Auckland was hammered after flash floods swept through the Waitakeres on Saturday, killing two people. Around 100 people were also evacuated, 60 of those from the Piha Mill Camp.
Forty-three millimetres of rain fell in the Waitakere Ranges in one hour, between 5pm and 6pm on Saturday. Residents of one street watched as the river quickly rose by metres, and then burst its banks, gushing through their homes as cars floated down the road.
Climate scientist Sam Dean says these downpours have become more common this hot summer.
"We are in a situation that is not normal... and we do know when those sea surface temperatures off the Tasman Sea are higher than normal. That is when we get our heaviest rainfall events."
And the Council warns this will only get worse.
Auckland Council commissioned NIWA to analyse projected climate changes for the Auckland region if global emissions continue on the current path.
The study finds the number of hot days, (days with temperatures above 25degC), could quadruple and average temperatures increase by up to 3.75degC by 2110 - leading to more extreme bursts of rainfall and increased flooding.