Aotearoa is surrounded by oceans, lakes dot both islands and rivers twist through the land – it's no wonder flooding is our most frequent natural disaster.
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 flood prone areas 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, the flow of water – and how built structures can either amplify or mitigate flood risks.
If you look at any regional council website in New Zealand, you'll find numbers for the likelihood that a flood of a particular size will happen.
Flood modellers can work out the likelihood by mapping out areas that have previously flooded 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 a property's flood risk, which not only predicts how big or powerful a flood may be, but also how vulnerable the home is. Therefore an area could be high risk, even for a small river splash-over, if, say, low-lying houses have been built right up to the river.
Recently Tower launched a model giving Kiwis a low, medium, high or very high risk rating for their home based on both the risk of a flood happening and the cost of repairing or replacing a damaged home.
CEO Blair Turnbull says it's not only a matter of understanding the impact of floods on homes but sharing the information with Kiwis so we can better shape and manage our collective futures.
"We are acutely aware of the climate risks faced by New Zealand," he says. "The launch of this model is aligned with Tower's commitment to a sustainable future and this means being open and transparent around insurance and risks associated with climate change."
Turnbull says while the introduction of the model meant a relatively small number of Tower customers saw a slight increase in premium, close to 90 per cent have seen the flood-risk portion of their premium reduced.
It's a positive start and while it should lead to fairer coverage and pricing across Aotearoa, the trouble with modelling flood risk is there's not yet a single standard for how it gets calculated.
"Everyone does it their own way," says Iain White, professor of environmental planning at Te Whare Wānanga o Waikato, the University of Waikato. "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 is part of a team, including scientists, councils, government and hapu, 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 to flood risk.
He says climate modelling like the work being done by NIWA (National Institute of Water and Atmospheric Research) is part of it but the other piece to the puzzle is understanding how the structures cities build impact flood risk – and how to lessen this 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," White says.
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.
Minimising flooding risk isn't just about where people build, it's also about how.
This content was created in partnership with Tower Insurance. To learn more about your property's flood risk rating, get started by clicking here.