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 failed to calculate how much the catastrophe magnified.
A flash study by 23 scientists from around the world on Tuesday found that global warming from the burning of fossil fuels added to Cyclone Gabrielle’s downpours that included at least six hours of deluges of nearly an inch per hour (20 millimeters per hour). ‘now) driving to rain. But the usual methods of quantifying the amount of climate change added to the disaster weren’t conclusive enough for the scientists because weather records aren’t that long ago, the affected area was relatively small, and the region is subject to naturally high weather variability. .
“Climate change is a serious concern with flooding in New Zealand, and you need to understand that it’s gigantic amounts of rainfall,” said Sam Dean, co-author and scientist at New Zealand’s National Institute of Water and Atmospheric Research. “I have no doubt in my mind with my life experience as a climate scientist that climate change influenced the event, but do we know it’s exactly 30%? No we do not.
The study is not yet peer reviewed, the gold standard in science, because it is such a recent event. But World Weather Attribution scientists follow well-established techniques for attributing climate change — comparing a particular event to simulations of what would have resulted without accelerated warming — and then publish their work 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 in New Zealand dollars) in damage to New Zealand, called Aotearoa in Indigenous Maori. In some places rainfall totaled as much as 15.7 inches (400 millimeters) in just two days, according to New Zealand’s Meteorological Service. The storm killed 11 people.
The cyclone hit just a couple of weeks after extensive flooding in the region had saturated the ground and basically lived up to New Zealand officials’ worst-case scenarios, according to the MetService.
Based on extrapolations from weather records dating back to 1979, heavy rains like that recorded over two days were about 30 percent more intense and four times more likely than in a pre-warming world that is 2.1 degrees Fahrenheit (1 .2 degrees Celsius) colder than Now. But the scientists said there are big uncertainties in those figures because there isn’t a lot of data.
Scientists also use computer simulations to see if global warming plays a role. But the area that was inundated is so small that most computer models can’t deal with it. Those that do might find a much smaller climate footprint than historical data shows, or virtually none at all.
However, the scientists said they are certain climate change played a role, although they cannot pinpoint an exact number.
University of Pennsylvania climate scientist Michael Mann, who was not part of the study team, said the team is likely underestimating the impact of climate change on New Zealand’s destruction because climate models in general are not enough to describe all the impacts of climate change on extreme conditions. weather.
“Human-caused warming means there’s more energy and moisture in every storm, whether a study formally attributes it or not,” he said.
In addition to climate change, the researchers found that a recently concluded La Nina phenomenon, which changes climate around the world, and an oceanic heat wave were contributing factors to Gabrielle’s impact.
“Any further warming will make these kinds of events worse,” said study co-author and team leader Friederike Otto, a climate scientist at Imperial College London. “Climate change isn’t something that’s going to happen in the future or to anyone else, but it actually affects people, especially vulnerable populations, it affects people all over the world today.”
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