New Research Reveals Need for Landslip Planning

Research from the University of Canterbury and Earth Sciences New Zealand suggests that under a warmer climate, future storms similar to Cyclone Gabrielle could become more extreme, triggering tens of thousands more landslides in vulnerable areas of the North Island and highlighting the need for targeted planning. 

In 2023, Cyclone Gabrielle triggered an estimated 800,000 landslides across the North Island, which researchers say makes it one of the most extreme landslide events ever recorded.

The study conducted by the University of Canterbury (UC) and Earth Sciences New Zealand examined landslide hazards in Tairāwhiti and Hawke's Bay under a +2°C warming scenario.

The researchers modelled how many landslides would have been triggered if Cyclone Gabrielle had occurred in this warmer climate. As well as the number of landslides increasing dramatically, the results suggest these new landslides are likely to occur in areas already prone to slipping, intensifying the hazard in already vulnerable locations.

Protect the future

Lead author, UC PhD candidate Livio Dreyer, said the research will empower planning that protects communities in the future.

"By combining landslide observations from Cyclone Gabrielle with climate and landscape data, we were able to build a picture of which slopes are most hazardous and how that hazard could change in a warmer climate. This helps turn complex modelling into information that can support real-world planning."

Study co-author, Dr Tom Robinson, Senior Lecturer in Disaster Risk and Resilience from UC's School of Earth and Environment, said the research represents a clear pattern for the landscape industry to consider.

"Slopes without forests experience far higher rates of landslides than slopes with forests. Indigenous forest is best, but even exotic forests act to reduce the rate of landslides. Bare slopes perform badly, so we should be looking to make use of vegetation as much as possible, even if it's not native vegetation."

NZ Landscaper contributor Jon Muller from Wellington Gardens says that landscapers must always check a slope's existing features when designing landscapes on them.

"For example, check to see if water runs down a slope into a neighbour's property or into a stormwater drain. You may need an engineer to check the condition of the structure – keep in mind that if it has been damaged by an earthquake, your client may be entitled to help from The Earthquake Commission.

"You may need to enlist the help of a drainlayer to check the stormwater. I recently used a drainlayer, who put a camera down a drain to show it was blocked, which was causing water to back up and damage pathways. Given the recent extreme weather, it's always good to be on the safe side when it comes to water movement."

Creating practical solutions

Dr Kerry Leith from Earth Sciences New Zealand said the findings demonstrate the importance of using climate science to inform practical adaptation measures.

"We can't prevent extreme weather events from occurring but we can reduce their consequences. Identifying high-risk areas and investing in targeted mitigation measures, including appropriate land management and vegetation cover, will help communities better withstand future storms."