new zealand It is grappling with two successive extreme weather events—massive floods followed by cyclones—that have claimed at least 12 lives and cut power to hundreds of thousands of people. Strong winds and flooding from Cyclone Gabriel swept away roads along the North Island coast, tearing apart and destroying bridges. Homes and streets were left under water just weeks after landslides covered runways in slick mud and heavy rains caused widespread flooding, prompting the country to declare a national emergency in its history. in only his third time.
New Zealand’s Minister for Climate Change, James Shaw, wasted no time in pointing out the root causes of the weather disaster, saying ‘this is climate change’ to the New Zealand Parliament.
He may be right, but evidence from imputation studies is yet to emerge, says James Renwick, a climate scientist and professor at Victoria University of Wellington. Cyclones themselves are not uncommon in New Zealand. Because they regularly move away from the tropics and come close enough to raise an alarm, he says. “We do these things reasonably regularly, some not so noticeable, some completely devastating,” says Renwick.
But global warming has raised ocean temperatures, which may have made the cyclone more intense, says Olaf Morgenstern, an atmospheric scientist at New Zealand’s National Institute of Water and Atmosphere Research. A hotter ocean means that if a cyclone hits, it will be stronger, it will contain more water and energy, and it will be able to hold that energy for longer, he says.
New Zealand is also experiencing marine heatwaves associated with La Niña, the cyclical Pacific weather system that has dominated the region for the past three years. These may have boosted the tropical cyclones. “It was unusually warm, so we didn’t lose a lot of strength. Even when we got here, we were pretty strong,” says Morgenstern.
A tropical storm preceded record rainfall and flooding that wreaked havoc on the North Island in late January. This also seems to be related to climate change. January broke the 100-year-old record as the wettest month in Auckland, with 539mm of precipitation recorded, half of that in his day. This was truly unprecedented, says Renwick, but the potential impacts of climate change on New Zealand would be more complex than just more rain.
Winds blowing from the west to the east have the greatest influence on the local climate. These bring heavy rains, especially on the west coast of the South Island. A famous fjord popular with tourists, Milford Sound is one of the wettest places on earth, with an average annual rainfall of 6.8 meters. The island’s mountains cast a rain shadow that expels atmospheric moisture as it passes overhead, leaving the east coast relatively dry.
But even subtle changes in wind direction and speed can lead to big changes in local climate, says Renwick. Climate modeling suggests that these westerly winds are likely to intensify. “Whether they’re lying so high above New Zealand is a difficult one to answer because there are some moving parts in the story. The increase in intensity is expected to bring more rain to the West Coast and less to the East Coast, which will lead to higher temperatures.
