The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
In January and February 2023, the largest city in New Zealand, Auckland, and its surrounding area was affected by two extraordinary rainfall events, triggering many thousands of landslides. In an open access paper just published in the journal Landslides (Brook and Nicoll 2024), Martin Brook and Chris Nicoll provide a brief but fascinating review of these two incidents. The implications for New Zealand are stark.
The first of the rainfall events, on 27 January 2022, was an “atmospheric river” that deposited 265 mm of precipitation, representing a one in 200 year return period event. The peak of the storm coincided with the Friday rush hour. The storm triggered one fatal landslide, in Parnell, a suburb of Auckland.
Just over two weeks later, Tropical Storm Gabrielle swept across the Auckland region on 13 to 14 February 2023. With the ground already saturated, this triggered further widespread landslides. There was a further fatal landslide at Muriwai on the coast to the west of Auckland.
Brook and Nicoll (2024) report that the two storms triggered over 140,000 landslides in total, causing damage that is estimated to be over US$8.6 billion, representing about 3.4% of New Zealand’s GDP.
The authors note that losses at this level are unsustainable, meaning that careful consideration is needed of the ways in which planning and land use are managed in New Zealand (and more widely). They make two important points. First, the planning system is allowing development of sites that are known to be hazardous; reform is needed. And second, the government-backed insurance scheme, EQC, which insures properties against landslide, earthquake and flood risk, has introduced a strong element of moral hazard as the levy that funds it is less than the true actuarial risk in many locations. In effect, the existence of EQC is discouraging people from managing the landslide risk facing their property and land. Again, this is probably an unsustainable position, although finding a way through the politics to address this issue is likely to be a massive challenge.
Reference
Brook, M.S., and Nicoll, C. 2024. Brief report of fatal rainfall-triggered landslides from record-breaking 2023 storms in Auckland, New Zealand. Landslides (2024). https://doi.org/10.1007/s10346-024-02258-0