The Increasing landslide susceptibility and intensity under climate change for Aotearoa New Zealand report says extreme rainfall from storms like Cyclone Gabrielle can trigger vast numbers of landslides, and warns those impacts are likely to intensify as the climate warms.

According to standard classifications, there are 32 different types of landslides, which are categorised by factors such as their failure mechanism, the speed at which they move and whether they’re constrained by topography, which could ‘super elevate’ material out of a channel.

Landslides are typically triggered by either earthquakes – which produced an estimated 40,000 landslide events when Kaikōura was struck in 2016 – or heavy rainfall, which can typically generate more than 10,000 landslides in a single major weather event.

Aotearoa New Zealand is especially prone to shallow landslides due to its steep topography, high number of earthquakes, and frequent severe weather events. Cyclone Gabrielle in February 2023 triggered 800,000 landslides across the North Island, and is one of the most extreme landslide-triggering storms recorded to date.

While research linking climate change and landslides in Aotearoa New Zealand remains limited – with only two studies focusing on Hawke’s Bay and Tairāwhiti using downscaled projections – this report uses Cyclone Gabrielle as a future “design storm” to assess landslide risks and improve understanding of potential impacts under a warming climate.

“Understanding how rainfall modulates landslide susceptibility and intensity is crucial for forecasting future hazards, particularly in the context of climate change,” the report said.

Under a +2°C warming scenario, a Cyclone Gabrielle-like storm could trigger up to 90,000 more landslides than the 2023 event, while the area experiencing extreme landslide densities could increase by up to 34%.

“Our findings suggest significant increases in landslide hazards due to climate change, providing an essential evidence base for land-use planning and targeted mitigation efforts in locations where landslide hazards are projected to intensify,” it said.

“Climate change projections for Aotearoa New Zealand indicate an increase in the frequency and intensity of extreme rainfall events. These changes are expected to amplify landslide hazards across susceptible landscapes, potentially increasing both the spatial extent of vulnerable areas and landslide intensities.”

The findings show new landslide-prone areas are likely to cluster around existing hotspots, suggesting climate change will intensify risks in already vulnerable locations rather than create entirely new hazard zones.

Recent projections for New Zealand suggest that while cyclone frequency may not change significantly, tropical cyclone intensity in the southwest Pacific could increase by 30–35% by the end of the century, reinforcing the likelihood of more severe rainfall-driven landslide hazards.

Warming-driven increases in the intensity of extreme rainfall are likely to drive a rise in both landslide susceptibility and severity.

“Our findings point to significant increases in landslide hazards under warming, likely concentrated in existing hotspots. Given the high probability of another Gabrielle-like storm in the coming decades (80% probability in the next 50 years), the outputs from this research are of immediate practical importance,” the report said.

“Our models quantify the degree of expected change and highlight the specific areas most susceptible to landslide intensification under a warmer climate. These findings allow adaptation efforts to be targeted effectively, providing an essential evidence base to inform land-use planning, prioritise mitigation investment, and enhance resilience in Aotearoa New Zealand.”

The research echoes earlier warnings that land use practices and development on unstable terrain are increasing landslide risks.

In 2023, following Cyclone Gabrielle, University of Auckland School of Environment Associate Professor Martin Brook said understanding the different kinds of landslides is the key to knowing more about New Zealand's shifting terrain.

He said some of the damage caused by landslides during Cyclone Gabrielle was preventable, with impacts exacerbated by human factors such as clearing trees and vegetation from slopes and cutting into hillsides for roads and residential developments.

“The soils are weak and very sensitive to changes in moisture content, very much the last place you’d build houses – but that’s where people were building.

“Land use change practices were causing a big problem in Gisborne, and it just makes the landscape less resilient when a big dump of rainfall comes along.”

Brook said climate change is expected to have an increased influence on the frequency of landslides because of extreme weather conditions, which include rainfall intensity and rising temperatures.

“It’s not just rainfall, but temperature extremes are probably an issue as well.”

Earlier this year the Government ruled out financial support for Gisborne District Council’s long-term storm and land-use transition plan, which the council says is needed to reduce damage and stabilise erosion-prone land.