Australia hasn’t been alone this past season in experiencing catastrophic flooding.
New Zealand’s run of deadly weather events has continued well into 2023. Just days ago, an 11-year-old boy disappeared after he and 14 of his classmates, accompanied by two teachers, got into difficulty on an outdoor education trip at Abbey Caves in Whangārei. Tragically, search and rescue teams later recovered the missing student’s body the following evening.
New Zealand has been impacted by multiple floods this year. La Nina conditions contributed to sustained maritime heatwave conditions over the area earlier in the year, with unstable northerly winds, and Cyclone Hale causing frequent heavy rainfall in January. This culminated in widespread catastrophic flooding late into the month and early February, particularly on 27th January when severe flash flooding hit Auckland. Cyclone Hale was a tropical cyclone and the first named storm of the 2022-23 South Pacific cyclone season. The cyclone formed over the Coral Sea on January 4, 2023, and tracked south-east towards New Zealand. It made landfall on the North Island on January 10, 2023. The heaviest rainfall was recorded in the Coromandel Peninsula, where some areas received more than 300mm of rain in 24 hours. The flooding caused widespread damage to roads, bridges, and homes. At least one person was killed in the floods.
Cyclone Gabrielle then devastated the North Island again in mid-February, killing 11 people and causing more than 8 billion dollars in damage, and considered by some the worst storm this century. The heaviest rainfall was recorded in the Bay of Plenty region, where some areas received more than 500mm of rain in 24 hours. This event can also be contributed to La Nina, with tropical cyclones more likely in La Nina events.
However, the flash flooding event that hit the Auckland area and parts of the North Island again on the 9th of May occurred under different climate drivers, with a neutral ENSO pattern, and rapidly moving towards an El Nino. However, very warm sea surface temperatures continue to surround the country right now, which have been known to increase the risk of flooding events (as seen by maritime heatwave conditions in January). Likewise, as also seen in January, strong and moist northerly winds were feeding into a trough, which generated thunderstorms with torrential rainfall and flash flooding as well as landslides, with up to 50mm falling in one hour. A state of emergency was declared.
Following the last round of downpours on the 9th, rapid damage assessments were underway with 100 homes and buildings flooded after an hours-long deluge swamped city roads and properties across the region. Auckland had up to 109mm worth of rain, with the heaviest rainfall occurring in Te Pai Park in Henderson where 103mm fell. Auckland city remained under a local state of emergency for more than a day afterwards, some roads still closed because of flooding with a risk that waterways would continue to rise with periods of heavy rain and thunderstorms still possible.
The deluge prompted the Auckland Mayor Wayne Brown to declare a third state of emergency in four months. MetService meteorologist Kathryn Hodge said the worst period of rainfall was between 10am and 1pm when Okura got 68.5mm worth of rain in two hours.
“It was a lot of rain spread out over the whole region.” Meanwhile, in Northland, the highest rainfall was in Kaikohe, which received 123mm worth of rain.
New research out of the University of Canterbury suggests that predictions of heavy rainfall can be improved.
PHD researcher Cameron McErlich explained on The Front Page podcast, how his research could help to ensure people in at-risk regions are better prepared for heavy rainfall. This is something already being achieved in Australia with Climatics.
“Through the research, we discovered that if you know how often it rains annually in one place you can make a strong prediction of the size and likelihood of extreme rainfall in that place,” McErlich said.
“By watching changes in rainfall occurrence, we can use our findings to understand regions where extremes might change. The findings are important because currently weather and climate research treat these things separately.”
City planners in at-risk areas can use this research to inform the decisions they make when building key infrastructure, such as stormwater systems. Cities with a higher likelihood of extreme rainfall events will need to be built differently than those with lower risks.
For example, cities in areas with a high risk of flooding may need to have more robust stormwater systems in place to prevent flooding. They may also need to build their infrastructure in a way that is less vulnerable to flooding, such as by raising buildings above the floodplain.
The Early Warning Network hopes to extend its Climatics platform to New Zealand in the near future. This will allow city planners in New Zealand to access the same research and data that is available to city planners in other countries. This will help them to make more informed decisions about how to build their cities in a way that is resilient to climate change.
