Why cyclones are now causing damage further inland; and the probable cause is a warming climate

As the tropical cyclone season concludes across the Pacific, recent systems affecting Papua New Guinea and New Zealand are underscoring how cyclone risks are extending beyond traditional coastal wind impacts.

UNSW Canberra researcher Dr Difei Deng said cyclones this season have highlighted the growing importance of rainfall, flooding and post‑landfall impacts, particularly in regions not traditionally considered cyclone‑prone.

“What we’re seeing more clearly now is that cyclone risk doesn’t stop at the coastline or even within the tropics,” Dr Deng said.

“These systems can continue to cause serious impacts well inland or far from where they first formed.”

This season, cyclones including Maila and Vaianu affected parts of the southwest Pacific, bringing heavy rain, strong winds and flooding to Papua New Guinea and New Zealand. While the systems followed different tracks and evolved in different ways, both demonstrated how tropical cyclones can continue to pose hazards after weakening or transitioning out of the tropics.

In Papua New Guinea, intense systems such as Maila produced multiple hazards, including destructive winds, extreme rainfall and landslides, particularly in mountainous and vulnerable regions. In contrast, Vaianu highlighted how a cyclone can weaken and transition into higher latitudes while still delivering damaging rain and wind to places in New Zealand.

“These examples show that there isn’t a single cyclone story anymore,” Dr Deng said.

“Some systems are extremely intense at landfall, others weaken but persist and some transition into different types of storms altogether, but they can all produce serious impacts.”

Dr Deng said understanding these pathways is critical for improving preparedness and risk communication across the region.

An important Australian case that helps explain these processes is Cyclone Oswald, which crossed the Queensland coast in January 2013. Despite reaching only Category 1 intensity over the ocean, Oswald went on to cause widespread flooding across Queensland and New South Wales.

Oswald did not weaken rapidly after landfall but persisted for more than a week and re‑intensified twice over land. It maintained a coherent circulation and tracked south along the coast, producing extreme rainfall and prolonged flooding well inland.

“Oswald fundamentally changed how we think about what happens after landfall,” Dr Deng said.

“It showed that a cyclone can lose its wind strength but remain highly dangerous because of rainfall and flooding.”

Oswald produced extreme rainfall totals, including more than 700 millimetres in parts of central Queensland, leading to widespread evacuations, infrastructure damage and economic losses exceeding $2.5 billion. Seven people died as a result of flooding and related impacts.

Dr Deng said the lessons from Oswald remain highly relevant when analysing recent events in Papua New Guinea and New Zealand.

“These systems may look very different on a cyclone category scale, but the underlying risk is often the same.”

“A weakened or transitioning cyclone can still deliver prolonged rainfall over large areas.”

There is growing evidence that rainfall‑related impacts are becoming more dominant as the climate warms. A warmer atmosphere can hold more moisture, increasing the likelihood of extreme rainfall even when wind speeds are relatively modest.

“As a result, wind‑based categories alone don’t tell the full story. A low‑category cyclone can still be a major flood event.”

She said this presents a particular challenge for inland communities, where cyclone risk has traditionally been viewed as a coastal issue. Recent events show that impacts can extend hundreds or even thousands of kilometres from the coast, lasting days or weeks.

“The biggest takeaway is the danger doesn’t end at landfall,” she said.

“The most damaging phase of a cyclone can occur after it has technically weakened, shifting the risk from wind to long-lasting water driven hazards.”