Impact of Flood Mapping on NZ’s Urban and Regional Planning

Flooding is New Zealand’s most common and costly natural disaster. A study from Earth Sciences, commissioned by the Infrastructure Commission, indicates that flooding will cost the country nearly half a billion NZ dollars by 2025.

This total includes expenses for private buildings (NZ$190.8 million), water infrastructure (NZ$68.4 million), local roads (NZ$46.9 million), and central roads (NZ$25.3 million).

The cost would rise by 45% to about NZ$682 million a year by 2075 under a medium greenhouse gas emissions scenario; by 50% to NZ$707.2 million under a “high” emissions scenario; and by 53% to NZ$721.3 million under a “very high” scenario.

Flood hazard and risk maps typically guide land use planning decisions in New Zealand; specifically, they examine the impacts of flooding in a particular area. Because of flood maps’ crucial role in land use planning, their scale – the level of detail and geographic coverage can also alter or dictate what land use decisions and risk management decisions a council or any governing authority makes.

The study, “The Role of the Spatial Scale in Flood Hazard and Risk Mapping for Informing Land-Use Planning: Insights From Aotearoa New Zealand”, published in the Journal of Flood Risk Management in June 2026 examines how flood hazard and risk maps are used to guide land-use planning decisions specifically examining the effects of spatial scale on these decisions amid the escalating flood-related damages which is compounded by climate change impacts and ongoing urban development in the country.

Integrating fit-for-purpose, updated flood hazard and risk maps is one of the challenges faced in land-use planning. This refers to appropriately scaled maps that are more applicable for informing land-use decisions. The study aims to address this gap by analysing empirical and documentary data on Aotearoa New Zealand to provide insights that support better urban flood risk management.

The study differentiates between the two types of flood maps – flood hazard maps and flood risk maps- which typically inform land-use planning. Flood hazard maps are engineering maps that show where flooding can happen and how severe it will be. They measure factors such as water depth, speed, and location.

Flood risk maps, by contrast, combine hazard information with the potential consequences or harm a flood will cause to people, the economy, culture, and the environment. The degree of harm or impacts also depends on the vulnerability of the inundated areas – the people, structures, and infrastructure that are present in the flooded areas.

Globally, the focus has been on flood hazard maps, which are used for land-use planning decisions and policies, rather than flood risk maps. This is mainly because flood risk maps are more expensive to produce.

The study uses New Zealand as a case study to show how different spatial scales of flood mapping can inform land-use planning decisions, given the country’s experience and heightened flood risks. Recent studies show that at least 675,500 people reside in flood hazard areas across New Zealand and over 400,000 buildings – with an estimated replacement value of NZD$134 billion are exposed to flooding.

The paper is structured as follows. It first reviews the different types of flood hazard and risk maps and how they are used in land-use planning, with a focus on spatial scale. It then presents results from document and empirical data analysis, highlighting key differences in mapping scales and their implications for land-use planning. Finally, the paper concludes that a fit-for-purpose flood hazard and risk analysis is needed, designed and implemented at the appropriate spatial scale.

Drawing on empirical data and document analysis, the study findings showed that most flood mapping in New Zealand focused on the meso (regional) and micro (local and site/property) spatial scales and that there was inconsistency in land-use planning decisions due to a lack of national guidance and directives on how to use flood hazard and risk information.

The author notes that the paper offers theoretical and practical insights on improved integration between land-use planning and flood risk management through the lens of the scale of flood hazard and risk mapping and its relationship with geographic and policy scales.

It helps land-use planning systems incorporate flood hazard and risk assessment across spatial scales in a more consistent and standardised way. In particular, the paper stresses the importance of using fit-for-purpose flood hazard and risk maps (at micro and meso scales) to inform spatial and strategic planning decisions at local and regional levels.

Learn more about the study: The Role of the Spatial Scale in Flood Hazard and Risk Mapping for Informing Land-Use Planning: Insights From Aotearoa New Zealand.