Scientists say climate change goosed New Zealand storm fury

Tropical Cyclone Gabrielle flooded New Zealand with gigantic amounts of rain last month and scientists say they are sure that climate change is a factor

Climate change worsened flooding from a tropical cyclone that shut down much of New Zealand last month in one of the country's costliest disasters, scientists said, but they couldn't quite calculate how much it magnified the catastrophe.

A flash study on March 14 by 23 scientists from around the globe found that global warming from the burning of fossil fuels added to the downpours from Cyclone Gabrielle that included at least six hours of deluges of nearly an inch per hour (20 millimetres per hour) of driving rain. But normal methods to quantify how much climate change added to the disaster weren’t conclusive enough for scientists because weather records there don’t go back very far, the area affected was relatively small and the region is subject to naturally high weather variability.

“Climate change is a serious concern for flooding in New Zealand and you've got to understand these are gigantic amounts of rainfall,” said Sam Dean, a co-author and scientist at New Zealand's National Institute of Water and Atmospheric Research. “I have no doubt whatsoever in my mind with my experience of my life as a climate scientist that climate change has influenced the event but do we know it's exactly 30%? No, we don't.”

The study is not yet peer-reviewed, the gold standard in science, because it is such a recent event. But the scientists at World Weather Attribution follow well-established techniques for attributing climate change — comparing a given event to simulations of what would have resulted without accelerated warming — and later get their work published in peer-reviewed journals.

More than 200,000 homes lost power for days on end, a nationwide emergency was declared and the storm caused $8 billion ($13 billion New Zealand) in damage to New Zealand, called Aotearoa in Indigenous Māori. In some places rainfall totaled as much as 15.7 inches (400 millimeters) in just two days, according to the Meteorological Service of New Zealand. The storm killed 11 people.

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The cyclone hit just a couple weeks after extensive flooding in the region had saturated the ground and essentially lived up to New Zealand officials' worst-case scenarios, according to the MetService.