New Zealanders are not yet in the clear when it comes to the dangers posed by landslides following the recent severe weather events that hit the upper North Island, according to NEMA.
The agency says the heavy rainfall earlier this week will continue to cause impacts for some days to come, including “widespread flooding damage, road closures, and the high risk of further landslides.”
The SMC asked experts to provide general information on landslides. Additional expert commentary on this week’s weather and landslides available here.
Dr Tom Robinson, Senior Lecturer in Disaster Risk and Resilience, University of Canterbury, comments:
“Landslides are historically New Zealand’s most deadly hazard, having killed more people in the last 200 years than all our earthquake disasters combined. As our climate continues to warm, the warmer atmosphere can hold more moisture leading to more frequent and heavier rainfall, which in turn is likely to cause more frequent landslides. Unfortunately, this means we should expect these kinds of storm events to become more common over the coming years. The risk from landslides in New Zealand is only likely to increase.
“While we can sometimes mitigate against landslides, this is often expensive and not always possible. Avoidance is often our best option – not building in locations where landslides are likely to occur. But for existing properties this is challenging, rarely do we ‘red zone’ a location before an event actually occurs. Even in locations where a landslide has occurred previously and a red zone been implemented, this history can be forgotten and the location re-inhabited, as we sadly saw in Muriwai in 2023.
“Over the coming years, we as a nation are likely to face some difficult decisions around how we manage the risk faced by landslides and other natural hazards. Importantly, we need to decide exactly how much risk we as a nation are prepared to tolerate before we are prepared to retreat away from high-risk locations.”
Conflict of interest statement: “None.”
Martin Brook, Professor of Applied Geology, University of Auckland, comments:
“The 200 mm of rainfall in 24 hours seen in parts of northern New Zealand would easily exceed the rainfall threshold to trigger landslides in many parts of New Zealand. The Bay of Plenty, Coromandel, Northland and Tairawhiti are always susceptible to shallow rainfall-triggered landslides after intense rainfall. The water weakens the surface soils and underlying highly weathered rock, causing shallow landslides to occur. The landscape often provides evidence of prior landslides, such as undulating surface topography, so rural landowners often are aware of landslide hazards on their land. However, landslides can also occur in steep road cuts so are visible to people, and impact traffic via road closures etc. We are still at the end of a La Niña, and La Niña conditions in the tropical Pacific tend to bring wet weather to northern New Zealand. Indeed, the recent deluge was predicted on the 10-day forecast two weeks ago on various weather websites.”
Conflict of interest statement: “Have received funding from the Natural Hazards Commission to study landslides”