30 January 2023
Multiple landslides from extreme rainfall in Auckland, New Zealand
Posted by Dave Petley
Multiple landslides from extreme rainfall in Auckland, New Zealand
In recent days Auckland and the surrounding area of New Zealand have suffered from an atmospheric river rainfall event that has been devastating, with the heaviest rainfall occurring on 27 January 2023. Met Service New Zealand tweeted about the 36 hour rainfall totals on 28 January:-
🌧 Rainfall totals so far during this event
📈 Many other stations around Auckland city recorded similar amounts between 250-300mm, with peak hourly rainfall of 60-80mm/h yesterday evening which are almost unheard of for NZ
💦 Rain still underway for most of the North Island pic.twitter.com/5xLoLQhP58
— MetService (@MetService) January 28, 2023
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Unsurprisingly, there has been extensive flooding and large numbers of landslides. Stuff has a really good portfolio of photographs of the landslides and flood that the rainfall triggered, whilst Newstalk ZB has this image of multiple landslides in the Massey neighbourhood of Auckland:-
Multiple landslides in Massey, Auckland. Image by Brett Phibbs via Newstalk ZB.
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Meanwhile at Remeura in Auckland a man was killed by a landslide that knocked a house off its foundations. Yahoo News has an image of the aftermath:-
The aftermath of a fatal landslide in Remuera, Auckland. One person was killed at this site. Image by Getty via Yahoo! News.
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Meanwhile, a large landslide has destroyed State Highway 25A across Coromandel:-
The aftermath of a large landslide that has destroyed SH25A during the extreme rainfall in the Auckland area. Image by WAKA KOTAHI via Stuff.
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Repairing this level of damage is going to be time consuming and expensive.
As I write there are warnings of further severe rainfall in the northern part of New Zealand, with a red rainfall warning in place for Auckland, Coromandel and Northland:-
Heavy Rain Warning (Red) issued for Auckland, Coromandel, Northland https://t.co/TRR3AupBsl
— MetService Severe Weather Info (@MetServiceWARN) January 30, 2023
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Further extreme rainfall could occur on Tuesday, with the mayor of Auckland warning that this could be even more dangerous than the rainfall that occurred on Friday. The challenge is not the rainfall total, which is likely to be considerably lower than on 27 January, but the presence of already saturated ground. This is a recipe for further landslides.
Already there is considerable soul searching occurring about the preparedness for these increasingly frequent rainfall events. A detailed review is going to be needed once the rainfall ends.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
Dave, you have captured it well. Some other things readers may wish to note:
(1) it’s been a wet La Nina summer (+ SOI for last few years) so unusual antecedent soil moisture leading up to Friday 27 Jan;
(2) possibly some distinctions with the rainfall-triggered landsliding in Gisborne we have seen over last 18 months (https://link.springer.com/article/10.1007/s10346-022-01982-9). In Gisborne, urban tree cutting and slope modification leaves many urban/suburban slopes exposed. Here in Auckland, plenty of landslides have occurred where people have purposely grown substantial tree cover to try and stabilise slopes – rainfall was just too intense, locally perched water tables etc.
(3) in NZ we have the EQC Act, which provides a govt insurance safety net scheme for natural hazards including flooding, landslips etc (details here: https://www.eqc.govt.nz/insurance-and-claims/natural-disaster-insurance/). In short, if you are a homeowner and already have purchased private insurance that covers a rebuild, EQC will pay up to NZ$300k; your insurer covers the cost over and above this.
(4) building setback distances – in Auckland, people love to have views – many multimillion $ houses are built close to steep slopes and cliffs with only a few meters of setback; alarming to some of us, given the weak nature of the Miocene sediments and residual soils.