By Tim Eldridge, Executive Advisor, Infrastructure Investment and Economics, GHD

Earlier this year, we were once again reminded how vulnerable parts of Aotearoa New Zealand can be to extreme weather events. Severe storms and flooding led to widespread disruption across the transport network, triggering landslips, rockfalls and debris flows, resulting in road closures that left some communities cut off from essential services.

These events feel all too familiar. Since Cyclone Gabrielle in 2023, we’ve continued to experience more intense rainfall, resulting in greater damage, longer recovery periods and significantly higher rebuild costs. The impacts stretch well beyond the immediate aftermath, affecting communities, supply chains and public finances. The Parliamentary Commissioner for the Environment noted¹ that spending on the environment has been consistent in recent years, but the composition has changed, with major increases in spending on recovery efforts ($666 million additional since 2023).

This prompts us to consider what’s required to make transport systems stronger, safer, and more resilient against Aotearoa’s changing weather conditions and natural hazards.

Since 2023, GHD has been working alongside the NZ Transport Agency Waka Kotahi (NZTA) as part of the South Island Resilience Panel to strengthen the long-term resilience of key transport routes. A deeper technical understanding of natural hazard risk enables a shift away from ongoing repair and recovery, towards proactive and preventive investment. As part of this panel, two single-stage business cases (SSBCs) and an investment case have been delivered, and are now in various stages of design and implementation.

High-risk sites across the state highway network are increasingly vulnerable to hazards caused by heavy rain and strong wind. For most of these locations, intensified rainfall is the primary trigger for road closures. Even small increases in rainfall intensity are causing rockfalls, slips, flooding and other forms of disruption. These routes serve as essential lifelines for remote communities and the tourism sector, yet they are frequently disrupted by storm events.

While forecasting future weather patterns remains complex, we do know that as global temperatures rise, extreme rainfall becomes more intense. NIWA estimates that for every one degree Celsius increase in temperature, short-duration extreme rainfall events – such as a one-in-100-year, one-hour storm – intensify by around 13.6 per cent.

Why do closures in remote locations matter?

These routes are often the only way in, out or through a region. At Epitaph, for example, the alternative route from Fox Glacier to Hāwea adds 516 kilometres – more than six hours for tourists, and even longer for freight. The impact on the regional economy, plus the extra transport costs, can run into tens of millions each month. While the full effects are hard to quantify, it’s clear that they are significant, and prolonged closures can even alter local economic patterns.

GHD and NZTA commenced the SH6 Haast to Hāwea SSBC in mid 2024, focusing on 20 high-risk sites, including the Epitaph site, located 22 kilometres north of Hāwea. This stretch of highway has a long history of repeated rockfalls, landslides, and major underslips that have challenged its resilience and reliability since it first opened in the 1960s.

By October 2024, we had begun 3D ground modelling and targeted site investigations to better understand the risk of major landslips, and to quantify the impacts from a prolonged road closure to local businesses, the community, the tourism sector and the freight industry.

Just one month later, in November 2024, a heavy rainfall event triggered significant rockfalls and road slumping, leading to a 13-day road closure of SH6 at Epitaph.

By early 2025, the ground modelling was complete, providing a much clearer picture of ground conditions, including likely failure mechanisms and longer-term impacts. In mid 2025, NZTA carried out emergency stabilisation works at the site, constructing a micropile wall to support the road and road edge. This helped to reduce the risk of underslips and further closures, while additional investigations and planning progressed to develop a longer-term solution.

In November 2025, the NZTA Board approved funding for the design and consenting of long-term resilience works at Epitaph. This approach fits with the Government Policy Statement on Land Transport 2024–27, which calls for smarter investment in resilience. By anticipating risks and acting early, the panel isn’t just reducing emergency response costs and limiting disruption; it’s helping communities recover faster and building infrastructure that serves people every day, not just in a crisis.

What have we learnt?

Resilience is at the heart of keeping New Zealand moving. While we can’t predict exactly when or where a major event might strike, we can improve our understanding of the risks, identify their causes and make targeted, proactive investments.

Through forward-thinking design, informed by technical expertise and local insight, this panel is helping to create transport systems that are ready to respond to future challenges.

Resilience isn’t just about the infrastructure itself; it’s about protecting the communities, businesses and people who rely on it every day.

End note

1 Budgeted government spend on environment similar to past year, with increased spend on extreme weather events and drops in other areas – Parliamentary Commissioner of Environment.