Nationwide Application of a Rapid Tsunami Inundation Model to New Zealand: Assessing Infrastructure and Land Exposure

Abstract. This study presents a comprehensive nationwide tsunami inundation assessment of New Zealand. It utilises wave amplitude data from a recent probabilistic tsunami hazard assessment (covering seven return periods at the 50th and 84th percentiles) and a computationally efficient tsunami inundation model. This modelling approach enhances the inundation accuracy of previous inundation exposure assessments, which have been limited by inconsistent and simplified inundation techniques. This study produces comprehensive nationwide inundation maps for 14 return periods along the entire New Zealand coastline. These inundation maps have been integrated with land cover and infrastructure asset data to assess New Zealand's potential exposure and identify the most vulnerable locations. The findings reveal that while commonly studied cities like Christchurch, Gisborne, and Napier are indeed highly vulnerable, significant exposure is also evident in many provincial areas such as the Buller, Westland and Thames-Coromandel Districts. In the Thames-Coromandel District, over 13,400 buildings are exposed to inundation at the 500-year return period tsunami amplitudes, representing 26.8 % of the buildings in the district. Considering the land classification, the 'Low Vegetation' land cover group is the most exposed in every region, while determining the exposure of the 'Built-Up Area' is a good indicator of overall asset exposure for a region. The inundation model’s efficiency, simplicity, and accuracy make it well-suited for international application, particularly in regions with similar topographic, land use, and hazard data. This versatility, combined with its speed, supports its application in further large-scale probabilistic hazard assessments and smaller, targeted scenario modelling, as well as in uncertainty analyses across diverse geographic and hazard contexts.