New Zealand is facing floods and fires

1 year ago

New Zealand fighting two consecutive extreme weather events – a massive flood followed by a cyclone – that have claimed at least 12 lives and left hundreds of thousands of people behind without power. Strong winds and the waters of Cyclone Gabriel washed away coastal roads on the northern island, and bridges shattered. Landslides covered asphalt with slippery mud and houses and streets were submerged, just weeks after heavy rains also caused widespread flooding. The country announced national emergency for only the third time in its history.

New Zealand Climate Change Minister James Shaw wasted no time in pointing the finger at the root cause of weather disasters. New Zealand Parliament: “It’s climate change.”

He may well be right, but the evidence for attribution is yet to come, says James Renwick, a climatologist and professor at the University of Wellington, Victoria. The cyclone itself is not unusual in New Zealand, he said, as it regularly crosses the tropics and gets close enough to cause alarm. “We queue for these things on a fairly regular basis. Some of them are not so remarkable, and some are just catastrophic,” says Renwick.

But our global warming may have increased the strength of this cyclone due to warmer ocean waters, says Olaf Morgenstern, an atmospheric scientist at New Zealand’s National Institute of Water and Atmospheric Research. Hotter oceans mean that if a cyclone hits, “it will be stronger, it will hold more moisture, it will hold more energy, and it will maintain its energy for longer,” he says.

New Zealand also experienced marine heat waves associated with La Niña, the cyclical Pacific weather system that has dominated the region for the past three years. This may have given rise to a tropical cyclone. “Because it was abnormally warm, it didn’t lose that intensity — it was still quite strong when it got here,” says Morgenstern.

Record rainfall and flooding preceded the tropical cyclone and wreaked havoc on the northern island in late January, also likely linked to climate change. January broke century record for Auckland’s wettest month, when 539 millimeters of rain was recorded, half of which fell in one day. It was truly unprecedented, says Renwick, but the likely impact of climate change on New Zealand will be more complex than just increased rainfall.

The winds that blow over the country from west to east have the greatest influence on the regional climate. They deposit huge volumes of rain, particularly on the western coast of the southern island. Milford Sound, the famous fjord popular with tourists, is one of the wettest places on Earth, with an average annual rainfall of 6.8 meters. The island’s mountains then force moisture out of the air as it passes over them, casting a rain shadow that leaves the east coast relatively dry.

But make even small changes in wind direction or wind speed, and you can get big changes in the local climate, Renwick says. Climate modeling suggests that these westerly winds are likely to get stronger. “It’s not easy to answer the question of whether they lie that much over New Zealand because there are a few moving parts to the story, but the overall picture is slightly stronger winds over time,” he says. An increase in strength is expected to result in more rainfall on the west coast and less on the east coast, resulting in higher temperatures.

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