It’s New Zealand. Battling two consecutive severe weather events, including severe flooding and storm surges that have killed at least 12 people and left hundreds of thousands without power. Cyclone Gabriel’s high winds and water have washed out coastal roads in the North Island and left bridges damaged and broken. Landslides have covered asphalt with slick mud, and homes and roads have been left under feet of water, weeks after heavy rains caused widespread flooding. The country has declared a national emergency for only the third time in its history.
New Zealand’s Climate Change Minister, James Shaw, wasted no time in pointing the finger at the root cause of climate disasters, telling New Zealand’s parliament, “This is climate change.”
He may be right, but evidence from attribution studies is yet to come, says climate scientist and professor at Victoria University of Wellington, James Renwick. Cyclones themselves are not unusual for New Zealand, as they normally spin through the tropics and come close enough to trigger an alarm. “We line up fairly consistently for these things. Some are not that impressive and some are downright awful,” says Renwick.
But a warmer planet may have increased the severity of this storm due to warmer ocean waters, said Olaf Morgenstern, an atmospheric scientist at New Zealand’s National Institute for Water and Atmospheric Research. Warmer oceans mean that if a hurricane hits, it will “get stronger, have more moisture, carry more energy and retain its energy longer,” he said.
New Zealand has experienced sea heat waves associated with La Nina, the cyclical Pacific weather system that has dominated the region for the past three years. These may have given impetus to the tropical storm. “Because it was unusually warm, it didn’t lose that much strength — it was still pretty strong when it got here,” Morgenstern said.
Record-breaking rainfall and flooding preceded the tropical storm and wreaked havoc on the North Island in late January – and it appears to be linked to climate change. January broke a century-old record for Auckland with 539mm of rain, half of which fell in a single day. That was truly unprecedented, says Renwick, but the impact of climate change on New Zealand will be more complex than just rain.
The biggest influence on the region’s climate is the wind that blows from west to east over the country. These put a lot of rain, especially on the west coast of the South Island. Milford Sound, where the famous fjord is popular with tourists, is one of the wettest places on Earth, with an average annual rainfall of 6.8 meters. As the mountains of the island pass over them, they force moisture out of the air, which makes the east coast relatively dry due to the rain shadow.
But introduce subtle changes in wind direction or wind speed, and they can make a big difference to the local climate, Renwick says. Climate modeling suggests those westerly winds could become stronger. “Whether they lied so much about New Zealand or not is a difficult question to answer, because there are only a few parts of that story, but the bigger picture is getting stronger over time,” he said. An increase in intensity is expected to bring more rain to the west coast, and less to the east, resulting in warmer temperatures.
