Auckland is flooding again - here's why climate change is to blame

Climate change is making extreme weather events more frequent and intense around the world, and New Zealand is no exception. Auckland and much of the North Island was hit with severe flooding in January and February of 2023 and these were some of the worst in the city's history, causing widespread damage and disruption. In May the storms brought more flooding, which once more brought disruption and the loss of life to the country. These 'once in a hundred year' events happened three times in the first 150 days of 2023. A clear sign that climate change is impacting the country's weather systems.

But how exactly did climate change contribute to these floods?

The main factor is the increase in sea surface temperature, which provides more fuel for tropical cyclones and other storms. New Zealand's Otago University researchers recently reported that the country's oceans are experiencing a record-breaking heat event, with temperatures up 1.6°C over the last year; and 2.4°C over the winter months. As the oceans warm, storms develop faster, become stronger, and reach farther from the equator. This means that places like Auckland, which are normally outside the tropical cyclone belt, experiences more intense rainfall from these storms.

Another factor is the increase in atmospheric water vapour, which is a result of warmer air holding more moisture. This means that when it rains, it rains harder, as more water vapour condenses into liquid droplets. According to an assessment by the World Weather Attribution team, extreme downpours now drop 30% more rain in the region than they did in a pre-industrial climate.

These two factors combined create the perfect storm for flooding, especially in urban areas like Auckland, where natural drainage has been severely reduced by rapid house and road building plans, leaving drainage systems unable to cope with such large volumes of water in a short time. All new builds in Auckland are required to include drain water storage systems, which hold water to prevent storm water drains from being overwhelmed, releasing the held water slowly over a period of time. The size and violence of the storms of 2023 has rendered even this measure ineffective. 

The floods  pose risks to public health, safety, and property, as well as environmental impacts such as erosion and pollution. Many homes were red-stickered after the January and February floods - meaning they were no longer safe for habitation - and in some places there was talk about implementing the country's Climate Change Adaptation Plan and abandoning whole areas in areas threatened by extreme weather events.

Once the Auckland Day floods and Cyclone Gabrielle were no longer front of mind, Kiwis carried on as normal; whilst Auckland Transport continued to offer a barely acceptable public transport service and the effects of climate change were mostly forgotten outside of the NZ Green Party. The early May floods were a nasty reminder that this sort of behaviour is going to create real difficulties for a country as exposed to weather events as New Zealand.

The Auckland floods are a stark reminder that climate change is not a distant threat, but a present reality that affects us all. To reduce the risk of future floods and other climate-related disasters, we need to take urgent action to cut greenhouse gas emissions and adapt to a changing climate.