A land-use modelling system commissioned by the Natural Hazards Commission Toka Tū Ake (NHC) has been developed to help councils and planners evaluate how zoning rules and infrastructure investment decisions could influence future flood risk.
The tool, designed by Market Economics’ Dr Robert Cardwell, runs virtual simulations to estimate how different policy approaches could change the location and type of urban development over time.
Cardwell noted that once land is zoned and built on, reversing those decisions is often impractical, making early risk assessment essential.
“Urban planning decisions are hard to reverse,” he said. “Once zoning rules are applied and infrastructure is built, the consequences last for decades. Our model helps avoid a situation where, 10 years after a development is approved, a major flood hits and people ask, "Why was this allowed in a floodplain?’”
Rather than predicting exactly where housing will be built, the model examines development drivers – such as accessibility, surrounding land uses, and population growth – to assess where high-risk construction might occur and what measures could reduce exposure.
According to current estimates, around 12% of New Zealand’s housing is located in areas prone to flooding, largely concentrated in urban centres in Auckland and Canterbury.
Despite this, housing continues to be developed in hazard zones, sometimes without sufficient mitigation.
In an Auckland-based test case, Cardwell modelled a scenario where floodplain areas were rezoned to a more restrictive category.
Over five decades, the model projected notable reductions in high-risk development, including fewer lifestyle blocks, standalone houses, and terraced housing projects.
Most of the displaced development shifted to neighbouring areas with lower flood risk.
Cardwell intends to expand the tool to include economic and transport modelling, enabling comparisons between the costs of repeated flood events and the benefits of alternative land-use strategies.
Study shows cyclone rainfall could increase
Separately, research from Earth Sciences New Zealand and the University of Waikato suggests that rainfall from tropical cyclones affecting New Zealand could intensify by up to 35% by 2100 if greenhouse gas emissions remain high.
The study simulated more than 1,800 years of cyclone activity under various climate change scenarios.
While the overall number of cyclones was not projected to rise, the frequency of stronger storms – Category 4 or above – was expected to increase.
Rainfall is forecast to show the most significant change, with wind speeds also strengthening but to a lesser extent.
The researchers attribute the rainfall increase to a warmer atmosphere’s capacity to hold more moisture, allowing storms to produce heavier downpours.
Historical events show potential losses
New Zealand typically experiences one or two ex-tropical cyclones a year, but severe events are infrequent.
Cyclone Gabrielle in 2023 and the Auckland Anniversary floods caused an estimated $14.5 billion in damage, of which insurers paid $3.8 billion in claims.
Advances in modelling resolution – from about 100 kilometres in older global models to roughly 12 kilometres in the latest regional simulations – are giving a more detailed picture of how storms could affect specific areas.
Global catastrophe losses remain elevated
The release of these findings coincides with a Willis analysis indicating that global insured losses from natural catastrophes in 2025 are likely to surpass $100 billion for the seventh straight year.
The largest single loss to date is the Los Angeles wildfire, with insured losses of more than $40 billion.
Article courtesy of insurancebusinessmag.com
