Flooding - both inland and coastal - is already one of New Zealand's most costly natural hazards, and the costs are rising. New research by Earth Sciences New Zealand, commissioned by the New Zealand Infrastructure Commission, Te Waihanga, examines how climate change could affect future flood damage to infrastructure and private buildings, helping inform long-term investment decisions.
This research builds on the Commission’s earlier Invest or Insure? report, which explored when infrastructure owners should reduce, transfer or accept natural hazard risk. Understanding the likely size of future losses is an essential first step in deciding which response is appropriate. The research uses average annual loss (AAL) to estimate the expected annual cost of flooding, providing a consistent basis for comparing risk across hazards, sectors and regions.
How scenario modelling can help us prepare for an uncertain future
Building on a previous phase, this research aims to explore three questions:
1. How do flooding losses vary between regions?
2. How are flooding losses expected to change over time in response to climate change?
3. How large are flooding losses to private buildings, which gives a sense of the need for flood protection?
Regional variation: As seen in the figure below, some regions are expected to face significantly more infrastructure losses than others, relative to the size of their networks. That means a localised approach to adaptation may be required.
Change over time: Infrastructure losses for coastal flooding are expected to nearly double over the next 50 years. Inland flooding losses are expected to increase by 50%, with much of those increases felt in the next 20 years. Total flood losses to private buildings are lower than total flood losses to infrastructure but are similarly expected to climb 50% over the next 50 years.
Resilience investment benchmark: The loss estimates provide a useful benchmark against which to compare the cost of risk reduction options, including new infrastructure, greater insurance, or strategies to avoid the risk, such as managed retreat. Where the cost of an option is lower than AAL, it likely represents value for money.
Building resilience into managing assets
Perhaps the report's most important insight is that resilience should not be treated as a separate planning exercise. Infrastructure owners will invest significantly in renewals as ageing assets reach the end of their lives. In many cases, natural hazard risk can be addressed alongside this routine asset management investment.
Better information to make better decisions
Better information about future flood risk helps infrastructure owners, council planners and local communities make more informed decisions today, strengthening resilience while making the best use of limited funding.
Learn more: https://tewaihanga.govt.nz/our-work/research-insights/when-waters-rise-research
