Photo: Dave Allen
Flood maps of Aotearoa New Zealand produced by Earth Sciences NZ show how much land is exposed to rainfall flooding with a 1% annual exceedance probability. These are floods that have a 1% chance of happening in any year. Over a very long period of time they might occur once every 100 years on average, but as we know from recent experience, it is also possible for them to occur twice or more within just a few years. (Earth Sciences NZ is a Public Research Organisation formed In 2025 when NIWA joined with GNS Science.)
Floods are happening more frequently
If you think that severe flood damage has been happening more often in recent years than it used to, you are right. Our warming climate means that a storm bringing extremely heavy rain that falls within the 1% annual exceedance category may be greater in severity. A flood that fell within the 1% category a few years ago is likely to happen more often in coming decades.
Resilience of the built environment is one of the key research topics that BRANZ is focusing on at the moment. You can find details of specific research projects underway on the BRANZ website.
We have also published bulletins on the topic, including BU700 Natural hazard information for building sites and BU701 Building on sites subject to flooding and/or landslides.