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Image: Getty Images, additional design by Tina Tiller
Image: Getty Images, additional design by Tina Tiller

Tower InsuranceJanuary 20, 2022

How can we predict and prepare for the floods of the future?

Image: Getty Images, additional design by Tina Tiller
Image: Getty Images, additional design by Tina Tiller

If we know what to expect, we can plan accordingly. But what does that mean when we’re talking about floods?

Aotearoa is a country of water. We’re surrounded on all sides by oceans. Lakes dot the motu. Rivers twist and wrap around our landscapes.

It’s perhaps no wonder then that flooding is the country’s most frequent natural disaster. It’s estimated that there were around 100 floods between 1968 and 2021. Predicting where the next big flood will be, and how bad it could get, could save heartache, homes and, in the most extreme cases, lives.

But designating areas that are flood-prone isn’t as simple as blocking out sections of land that are close to rivers or the sea. Understanding flood risk means understanding climate change, weather patterns, geography and water flow, and how built structures amplify or hold back floods.

Look at any regional council website in New Zealand and you’ll find numbers for the likelihood that a flood of a particular size will happen (here’s Wellington’s for example).


This content was created in partnership with Tower Insurance. To learn more about how flood risk works and to speak to an expert about your own property risk profile, get started by clicking here.


Flood modellers can work out that likelihood by mapping out areas that have flooded in the past and making models that include things like rainfall, water volume, flow speed, and land roughness.

But the likelihood of a flood happening is different from flood risk. Flood risk not only takes into account how big or powerful a flood is but also how vulnerable a nearby area is; vulnerable to losing buildings, losing or disrupting lives, or losing money in repairs. An area could be at high risk, even for a small river splash-over, if, say, low-lying houses have been built right up to the river. 

Tower Insurance recently launched a model that gives their customers a low, medium or high risk rating for their home, based on both the risk of a flood happening and the cost of repairing or replacing their damaged home. For Tower CEO Blair Turnbull, it’s a matter of understanding the impact of flood on homes and businesses, and sharing that with customers and communities to better shape and manage our collective futures.

“We are acutely aware of the climate risks faced by New Zealand. The launch of this model is aligned with Tower’s commitment to a sustainable future and being more open and transparent around insurance and risks associated with climate change,” Turnbull says.

And while the introduction of the model did mean that a relatively small number of Tower customers saw a slight increase in premium, close to 90% have actually had the flood-risk part of their premium reduced. 

A Kumeu resident surveys the damage during the region’s 2021 floods. (Photo: Fiona Goodall/Getty Images)

It’s a positive start, and one which should lead to fairer coverage and pricing across Aotearoa. The trouble with modelling flood risk at the moment, though, is that there’s not yet a single standard for how it gets calculated. “Everyone does it their own way,” acknowledges Iain White, professor of environmental planning at the University of Waikato, and an advisor to Tower Insurance.

“There are different definitions, thresholds and methodologies so we don’t have a great picture of the national flood risk because we do it slightly differently in different areas,” White says.

White’s part of a team, including scientists, councils, government and hapū, creating a national, open source flood risk map – using the same methods across all areas.  

His particular focus is on including predictions of how climate change will influence regional weather patterns, and how that links in to flood risk. A warming atmosphere makes extreme weather events – including heavy and sudden rainfalls that are a key ingredient to flooding – more likely, says White. 

It’s hard to predict which area is going to be hardest hit, he says. “Even if in some areas rainfall remains the same on an annual basis, it’s just going to be distributed differently. You might get drier periods and then bigger, wetter dumps.” It’s those sudden downpours that can overwhelm a river or stormwater system.

Climate modelling like the work done by Niwa is part of it. The other piece to the puzzle is understanding how the structures cities build impact flood risk – and how to lessen that risk through better building.

“What climate change means is that what water lands on – pipes, drains, landscapes – will have to deal with volumes they probably haven’t been designed for,” says White. 

With a greater need for more and denser housing, these kinds of flood risk models can tell councils and developers where to build more densely (low risk areas) and where to ease off. 

Areas that aren’t suitable for housing could be great multi-use areas, says White, that are recreational, habitats for wildlife and, importantly, can store rainwater. Water catchments (like these beautiful urban gardens or ponds) move water off concrete, out of drains and off roofs, slowing down water flows and water pooling. 

And minimising flooding risk isn’t just about where people build, it’s also about how

Ryan Paulik is a Hazards Analyst with Niwa. “We’re really starting to build a picture of where floodplains are. Once we have those flood maps we can actually start to look at what’s in those floodplains and what’s the damage and loss that’s likely to occur from a modelled flood scenario,” he says.

A rest area in Kaiapoi, Canterbury sits underwater during the Waimakariri river floods in mid-2021. (Photo: Kai Schwoerer/Getty Images)

Paulik has gone to the aftermath of six of New Zealand’s most recent floods, including the ones in Edgecumbe and Westport, to understand how buildings dealt with the floodwaters. He collects data on how buildings are damaged and then translates that into a model of how vulnerable particular building types are.  

In Edgecumbe, a large proportion of the homes were built in the ’70s and ’80s with chipboard flooring. When the homes got wet, that flooring would warp, meaning the damage was more severe than homes with different flooring types.

And in the case of the 2014 Christchurch floods, houses on concrete slabs were more vulnerable. “We visited some sites where there was an early 20th century villa on the front of the property and a newer building on a concrete slab sitting at the back. The old villa up on piles had no water through it and then the building at the back had half a metre,” he says.

These models that Paulik and others provide can be used in a number of ways. Councils could, for example, create guidelines around what materials new builds use or how they’re constructed. Or insurance companies could more easily factor building type into the cost of a premium.   

Both White and Paulik emphasise how important this kind of modelling work is given our changing climate – as White says, “Even if we can’t predict exactly how climate change will play out, we can make it so it’s less costly for future generations by thinking about design and risk.”

And with insurance companies like Tower actively trying to ensure their pricing and offering takes flood risk into proper account, the end result of getting that work right should ultimately be a system that’s better and fairer for all of New Zealand.

Keep going!
Kids navigate heavy flooding in Edgecumbe, 2004 (Photo: Michael Bradley / Getty Images; additional design by Tina Tiller)
Kids navigate heavy flooding in Edgecumbe, 2004 (Photo: Michael Bradley / Getty Images; additional design by Tina Tiller)

Tower InsuranceJanuary 13, 2022

High water, rising costs: a recent history of floods in New Zealand

Kids navigate heavy flooding in Edgecumbe, 2004 (Photo: Michael Bradley / Getty Images; additional design by Tina Tiller)
Kids navigate heavy flooding in Edgecumbe, 2004 (Photo: Michael Bradley / Getty Images; additional design by Tina Tiller)

Flooding has long impacted Aotearoa, but the recent past has seen more, bigger flood events than ever before. What’s changed? 

The rains came fast and hit hard. Downpours, brought on by ex-tropical cyclone Debbie, battered the Bay of Plenty region. 

It was more than the small town of Edgecumbe could bear. 

After days of straining against rising river waters, the concrete floodwall separating the Rangitāiki River from the town leaked and eventually burst, unleashing cascades of water. Edgecumbe became awash with flooding and debris. 

At around 8:30am on the morning of April 6, 2017 those living in the town were told to leave their homes to seek higher ground. Some never returned to those homes. 

Edgecumbe isn’t an isolated event. New Zealand’s history is riddled with severe floods – around 100 over the past 60 years, and nine in the past 14 months alone – which have washed through townships and displaced families and entire communities. 

With such a full history of floods, were there signs that they were going to happen? And how does climate change play into how predictable, and severe, future floods are going to be?


This content was created in partnership with Tower Insurance. To learn more about how flood risk works and to speak to an expert about your own property risk profile, get started by clicking here.


The timeline of events leading up to April 6 seem straightforward: heavy rain, swelling river, stopbank burst. But according to the late Sir Michael Cullen, who led a 2017 independent review of the flood, the situation was “complex”.

Floods are caused one of three main ways. Rain or snow melt can cause rivers to swell and overflow, also called a fluvial flood; rain can hammer concrete surfaces and overwhelm stormwater systems, known as pluvial flooding; or ocean waters can sweep up high onto land: coastal flooding. 

A flooded home in the aftermath of Edgecumbe’s 2004 floods. (Photo: Michael Bradley/Getty Images)

Three days before the Edgecumbe flood, MetService had issued a warning for heavy rain, culminating in predictions of 200 to 350mm of rain in less than two days. The other factor at play was that the previous month had been very wet as well, meaning soils were already soaked from high rainfall. 

Heavy rain and wet soil combined to cause both the Whakatāne and Rangitāiki rivers to swell, with the Rangitāiki about 20% more full than during the previous 2004 flood. 

The weather signs were there; how the region dealt with their consequences came down to its flood management plan.  

Edgecumbe’s main lines of defence were the nearby Matahina dam, which could store some of the floodwaters if water was drained out of Matahina lake; the Reid’s floodway, which would divert floodwaters away from the city; and its various floodwalls along the river, which should have held the floodwaters back.  

The 2017 report identified that Trustpower, which was in charge of operating the dam to lower lake levels ahead of heavy rain, was slow off the mark and communication between the local council and the organisation broke down at times. It’s unlikely though that changes would have prevented the floodwall from breaching, the report concluded.

The floodway was outdated and undergoing a years-long upgrade, including widening the floodway to accommodate more water. Design issues, landowner negotiations and dodgy modelling of its capabilities all contributed to delays in getting the floodway upgrade completed by 2014. If it had been, it’s likely there would have been less pressure on Edgecumbe’s last line of defence: its floodwalls.

Wedged between the town and the river sits the College Street floodwall, adorned with brightly-coloured paintings of fish and hillsides. The wall had already withstood earthquakes, previous floods and slumping of the river bank, creating cracks in its foundation and leaks in its face. 

Twenty minutes before it burst, residents noticed water seeping from the wall. That seep turned into a fountain up to a metre tall spurting from the concrete. One fountain turned into several. Finally, the wall cracked open “like two gates” unleashing water upon the town. 

After some 160 pages, the report concludes that the framework that manages flooding events, the 1970 Rangitāiki River Flood Scheme, is past its use-by date. It made several recommendations about how to beef up the scheme and infrastructure, including the floodwalls and floodway. 

Downpours in Kaeo, Northland led to heavy flooding in 2012. (Photo: Sandra Mu / Getty Images)

But not all floods can be traced back to something as dramatic as a concrete barrier failing. Northland’s 2020 flood saw rivers and streams swell but also water collecting on concrete surfaces and in low lying areas. 

After months of droughts, more than 200mm of rain fell on the region, causing slips that closed the main highways and water to pool and eventually inundate homes. 

Both floods would have emotional, legal and economic consequences. Years later, school children in Edgecumbe would cower under tables when it rained heavily. Other residents would speak about how traumatic and lonely the past few years have been. 

Homes were left uninhabitable, some caked in mud and debris; others were completely washed away or their foundations destroyed. Insurance claims for lost or damaged homes and belongings totaled in excess of $91 million in Edgecumbe and $37 million in Northland. 

Various factors contribute to a home’s flood risk. According to Tower Insurance, these can range from the number of floors to the building materials and flow of water. New technology developed with analysis from Risk Management Solutions and brought to New Zealand by Tower gives homeowners and insurers a much clearer picture of the individual flood risk of a property, says Tower CEO Blair Turnbull.

“The benefit of using the RMS model is that it is so detailed that neighbouring properties can have very different ratings, depending on the camber of their land, whether they have a flood wall, and other factors.”

New Zealand has been rated one of the worst countries in the world for natural disaster risk, and this modelling helps homeowners and potential owners to make the best decisions for themselves. Each customer is given a low, medium, high or very high rating for their flood risk, which also brings down insurance prices for those in lower-risk categories.

Tower Insurance CEO Blair Turnbull (Photo: supplied; additional design: Tina Tiller)

“Ninety per cent of Kiwis told us that access to flood risk data about a house they are looking to buy may change their thinking about the property in some way. We also know that only one in three Kiwis feel very confident that they have the right level of insurance for their current house to cover the risk of flooding by waterways and rainfall,” says Turnbull.

In the Edgecumbe and Northland floods, it was not just homes that were lost, but many farming businesses too. Farmers lost fences and animals, and had a huge cleanup job on their hands, all while trying to keep their animals free of diseases spread by dirty floodwater.

After each event, New Zealand’s scientists have issued a stark warning: be prepared because extreme floods are going to happen more often because of climate change.

The 2017 Edgecumbe report stated there’s “near-certainty that climate change is leading to more severe and more frequent extreme weather events of the sort that occurred in April [2017]”.

According to Iain White, professor of environmental planning at Te Whare Wānanga o Waikato, The University of Waikato, “those big, strong, short, sharp dumps of rain we get a lot of recently, we’re due to get more of them”. That’s because as the atmosphere warms, it can hold more moisture, which then falls to the earth in big dumps. 

It also means atmospheric rivers, large pools of concentrated moisture in the atmosphere, are more likely. Rising sea levels means coastal areas are more vulnerable to flooding. And warmer ocean temperatures are a great starting point for tropical cyclones or hurricanes, like the one that fueled the heavy rains near Edgecumbe. Climate change is set to make those storms more intense, the National Institute of Weather and Atmospheric Research (Niwa), Taihoro Nukurangi predicts. 

Scientists are already able to see how much climate change contributes to recent New Zealand flooding events. They create models of what a weather event would have been like if greenhouse gases weren’t higher, as they are today. For example, almost half the risk associated with the Northland floods could be pinned to climate change. 

It’s called attribution science and researcher Sam Dean says it has a big role outside of science. “Attribution has a really strong role in communicating with people the idea that climate change is the here and now. It’s not something for the distant future,” he told Stuff.

But it’s tricky. As Edgecumbe and Northland demonstrate, it’s an interplay between climate change, the weather it creates, built structures and people’s responses to circumstances and attitudes towards risk. 

“It’s quite uncertain,” says White. “One of the things we’re trying to do is bring knowledge together and understand more. So we get modellers working side by side with planners so that we can make better decisions now.” 

That side by side approach, White hopes, will save people heartache, homes and money in the long run.