Cyclone Gabrielle Was Intensified By Human-Induced Global Warming

A new NIWA-led study has found that climate change increased the amount of total rainfall during Cyclone Gabrielle by 10%.

This additional rain fell during the most intense parts of the storm, suggesting climate change had an amplified effect on the flooding that occurred.

This comes after The Treasury announced yesterday that there is an 80% chance of another Cyclone Gabrielle in the next 50 years.

NIWA climate scientist Dr Dáithí Stone says that if the world continues to warm at its current rate, these storm events are likely to become even more extreme.

"Cyclone Gabrielle resembled some of the worst-case scenarios that we could have predicted for the region. We therefore wanted to see how much climate change influenced its power, so we compared the actual MetService forecast of the storm against forecasts under conditions representative of a climate without human interference. Our study found a significant increase in rainfall under human-influenced conditions," said Dr Stone.

The team also looked at what may have happened if the world was even hotter than now and found that there would have been more rain still.

Since the industrial revolution, human-induced climate change has increased average global temperatures by at least 1.1-C.

This has led to more intense storm events - a warmer atmosphere holds more moisture, which provides fuel for storms and increases wind speeds.

"Our findings resemble results from similar experiments looking at tropical cyclones elsewhere in the world, so it’s not something specific to New Zealand. The best way to tackle future storms is to reduce our greenhouse gas emissions to halt, or even reverse, the warming of our climate. But until then, Cyclone Gabrielle must form our new benchmark for preparing for any future natural disaster," said Dr Stone.

Chief Meteorologist at MetService Chris Noble said this research is vital..

"The results of this study are incredibly helpful to quantify the influence of climate change on storms in Aotearoa New Zealand. We know the world is warming and the approach we’ve used gives unique insights into how quickly the severity of storms is increasing.

"Studies like this help the public understand climate change impacts here in New Zealand and may help inform policy and adaptation strategies in the future," said Mr Noble.

Cyclone Gabrielle formed in the Coral Sea and struck the northeast of Aotearoa New Zealand as an ex-tropical cyclone in February 2023.

During the event, rainfall totals reached nearly 450mm, which is roughly a quarter of the usual amount in an entire year. Rainfall intensity peaked at nearly 40mm per hour in some places.

It was one of the worst natural disasters in New Zealand’s history, claiming the lives of 11 people and causing damage estimated at $13.5 billion.

Notes

The research was carried out with collaborators at MetService, Bodeker Scientific, the University of Waikato and the Norwegian Meteorological Institute.

An earlier rapid study released shortly after the event by the World Weather Attribution group, working with NIWA and other New Zealand researchers, analysed rainfall observations to suggest that storms could be expected to bring 30% more intense rainfall due to climate change. The current study led by Dr Stone instead looked at how climate change affected Cyclone Gabrielle specifically.

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