Dr Kerry Leith1, Dr Chris Massey2, T. Robinson3, B. Lukovic4, S. McColl4, T. Carey-Smith4, B. Rosser4, L. Wortherspoon5, H. Smith6, H. Betts6, R. Buxton4, J. Bidmead4.
1 Engineering Geomorphologist, ESNZ – GNS
2 Engineering Geologist, ESNZ – GNS
3 University of Canterbury
4 Earth Sciences New Zealand
5 University of Auckland
6 Bioeconomy Science Institute
k.leith@gns.cri.nz
In February 2023, Cyclone Gabrielle brought record rainfall to the North Island, triggering more than 160,000 landslides. Our study looked closely at over 116,000 of these landslides in Hawke’s Bay and Tairāwhiti to understand what controlled where they happened.
The key finding is that while heavy rain was the main trigger, the relationship is not simple. Once rainfall passed very high levels (more than 220–330 mm in 24 hours), the amount of rain became less important than other factors such as slope steepness, soil type, and land cover. In some places, rain was so extreme that the soil was already fully saturated, meaning the usual effect of “how wet the ground was before the storm” didn’t matter.
This means that during severe storms, the areas most at risk are not always those with the highest rainfall totals. Instead, land characteristics like geology, soil depth, and whether slopes are forested or bare play a bigger role in determining where slips occur.
This research shows that managing land cover and soil health can make a real difference to landslide risk, especially as more frequent extreme storms are expected with climate change. Understanding which parts of the farm are most vulnerable can help with planning, reducing damage to land, stock, and infrastructure in future storms.
This research is published in:
Massey C, Leith K, Robinson TR, Lukovic B, McColl S, Carey-Smith T, Rosser B, Wotherspoon L, Smith H, Betts H, et al. 2025. What controlled the occurrence of more than 116,000 human-mapped landslides triggered by Cyclone Gabrielle, New Zealand? Landslides 1–20. https://doi.org/10.1007/s10346-025-02591-y
This study was funded by New Zealand’s Ministry of Business, Innovation and Employment, Award Number: C05X170 and C05X2304.