An eye-watering 24.5 centimetres of rain fell on Auckland in the course of 24 hours from Friday morning to Saturday morning. The torrent shattered the previous record for Auckland’s wettest day (16.1 cm), bucketing more than half as much water again on the nation’s largest city.
It was a level of ferocity no one was expecting. There were weather warnings and news articles ahead of time but no one was prepared for the battering the city took on Friday night.
Thanks to NIWA’s online collection of decades of weather measurements from stations across Auckland, Newsroom has put together five graphics which show the scale and speed of the devastating storm.
The record-breaker
The longest running weather record which is still active comes from a station at Auckland Airport. Major storms in 1985 saw 161 mm of rain fall at the airport, setting a record that lasted nearly four decades.
But Friday’s biblical shower broke that record, as the chart below shows. The 245 mm of rain the station received between 9am Friday and 9am Saturday towers over every single other day across more than 60 years of data.
A whole season in one day
A quarter of a metre of rainfall in one day is unprecedented. To give further context, we’ve looked at the amount of rain Auckland Airport might expect on an average January day, through all of January on average and across the whole summer.
The torrential storm of Friday night dumped more water on the city than it would typically see in three whole months.
Devastatingly quick
The barrage wasn’t spread evenly over the course of the day, either. The video below shows how much rain was detected in Mangere in five minute intervals.
From sunrise, the city endured a steady level of rain, but the deluge hit twice – once between 4pm and 5pm and then again between 6 and 7:30. In a 22-minute period from 6:50pm to 7:12pm, 39 mm of rain fell on the city.
In fact, in just the 50 minutes to 7:12pm, Auckland saw more rain than it usually sees across the whole of January. The peak came at 7:10pm, when 4.2 mm fell in just two minutes.
Unevenly distributed
Not every part of the city was hit equally hard. The greatest rainfall was registered in south and central Auckland and the North Shore. Even so, of the 76 weather stations in Auckland which have reported their data from Friday’s storm, all but six reported above 10 centimetres of precipitation.
One of the root causes
This chart isn’t about rainfall. It’s about temperature.
That’s because we know that climate change is already making storms more frequent and more extreme. It will be a little while before scientists at the Extreme Weather Event Real-time Attritbution Machine (EWERAM) project can tell us how much more intense this event was because of climate change.
What we do know, however, is that the atmosphere holds 7 percent more water for every degree it warms. We’re at 1.1C of warming already.
We also know EWERAM previously found devastating ‘atmospheric rivers’ (narrow corridors of concentrated moisture in the atmosphere, sometimes called cloud rivers) in Westport and Canterbury in 2021 were made 10 to 15 percent more intense by climate change.
And the Intergovernmental Panel on Climate Change (IPCC) says, globally, extreme precipitation events are already a third more likely to happen and will be on average 6.7 percent wetter based on current warming. At 2C, these storms will be 50 percent more common and 10.5 percent wetter.
Based on current policies, the world is on track for 2.6C.
So while this storm may well have still happened without climate change and may still have been devastating, the fingerprints of a warming world will be on almost all of our extreme weather events from now on.
