Flood risk data highlights our collective vulnerability

The release of the first national flood risk model by Earth Sciences last week marks a pivotal, if uncomfortable, moment of clarity for Aotearoa. For the first time, we have a nationally consistent picture of flood exposure, moving beyond the fragmented and disparate assessments held by individual councils.

The data paints a stark portrait of our collective vulnerability. About 750,000 people, 15 percent of the population, are already exposed to a 1-in-100-year flood event, and the value of buildings standing in harm’s way is a staggering $235 billion rising to $288 billion under a 3C warming scenario.

This is not merely an exercise in mapping; it is a national ledger of our past planning decisions. For decades, we have been making high-stakes adaptation choices in an information vacuum. That era is now over. The question is no longer whether we are at risk, but where and by how much.

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This dataset forces us to confront a legacy of poor land-use decisions. It also reveals a profound gap in climate justice. The maps visualise inequity as clearly as they show inundation. Some of the regions most exposed to severe flood risk are those least equipped to cope with it. The West Coast, for instance, has the highest proportion of its population at risk to exposure (34 percent), yet operates with a small ratepayer base and a lower-than-average median income.

This is the critical truth: some areas and the communities that live there are more vulnerable than others and less equipped to deal with it. As the researchers highlight, we risk falling into a maladaptation trap, where adaptation investment flows not to the places of greatest need, but to those of greatest capacity. Wealthier councils can commission detailed modelling and advocate for investment, while others – often those with the highest risk and lowest resources – are left behind.

The result is a systemic failure in governance. Those who can least afford to leave a flood-risk area are left vulnerable to harm. This is not a failure of data – we now have that – but a failure of decision-making that has allowed our urban development to proceed without a clear (or fair?) view of who bears the cost.

This new national model is not an endpoint. It is a diagnostic, and like any diagnostic, its real value lies in how it informs response. To design robust adaptation, we must acknowledge what the model does not show. Its limitations are clearly stated, and they must guide our next analytical steps.

The model covers inland pluvial (rainfall) and fluvial (river) flooding, and though it incorporates tide data at river mouths and accounts for key stop-bank defences, it still doesn’t include a comprehensive national assessment and management of coastal storm-surge and sea-level rise flooding – elements that remain under development within the proposed National Flood Map.

A viewer for coastal flooding has been available for several years now, providing 1% AEP storm surge data across the country. Users can apply sea level rise scenarios to see how inundation patterns change. However, this information isn’t integrated with other hazard datasets, making it difficult to assess combined impacts. We understand that ESNZ (Earth Sciences NZ) is working to bring this information together, including council data, through future updates.

This is particularly significant for an island nation where much of the population, infrastructure, and economic activity are concentrated along the coast. Until these risks are fully incorporated, a truly holistic national risk picture remains dangerously incomplete.

Moreover, the dataset distinguishes exposure, but not vulnerability. The data proficiently maps which assets are in harm’s way – $235b in buildings, 19 percent of the road network, and 40 percent of stormwater pipes – but it does not show what happens when those systems fail. What are the cascading social and economic impacts when roads, water, and housing are cut off? This is the critical distinction between a hazard inventory and a systemic risk assessment – and the latter must now be our goal.

Identifying these analytical gaps is not a criticism of the model but clarifies what next steps are required. Although this dataset is a foundation, we must now build on it by funding the next generation of analysis that integrates coastal hazards and cascading failures across infrastructure systems that our cities will face.

But let’s not think of the national risk model as a “doomsday map”. Rather, it is the essential enabling tool we have been missing. Its greatest immediate power lies in prevention. The data provides a robust, evidence-based mandate for local authorities to finally stop our very good but deeply perilous habit of developing on the lovely flat land next to rivers. This tool empowers planners and councils to make an objective justification for avoiding risky development proposals, thereby breaking the cycle of ad hoc development decisions that have entrenched exposure to flooding over decades.

However, the true opportunity is not in the map itself, but in how we use it. The researchers’ stated aim was to support “national policy development” and “prioritisation and investment planning”. The maps give us the ability to move beyond localised, reactive responses and ask the hard, strategic, national-scale questions we have so far avoided:

Which adaptation plans deliver the most cost-effective resilience outcomes?
How do we prioritise investment to achieve the best results for communities?
And, crucially, how can central government design a national adaptation framework that provides sustained financial and technical support to the low-income, high-risk regions that this data so clearly identifies?
This national flood model offers the diagnostic. The treatment must be a transformation in governance – one that ensures climate adaptation is not a luxury for well-resourced councils but a right for every community.

With the data now in hand, we no longer face a crisis of information, but a test of will. The next chapter of adaptation in Aotearoa will be written not by our maps, but by our choices: whether we use this knowledge to build a more resilient, prepared, and – above all – more equitable nation.