Evaluating national population and built-environment exposure to fluvial and pluvial flooding

Consistent national assessments of flood hazard-exposure are required to meet Sendai Framework for Disaster Risk Reduction monitoring obligations, yet remain rare globally. This study applies a spatiotemporal model integrating 100-year annual recurrence interval hydrodynamic fluvial and pluvial flood hazard simulations with population and built-environment exposure datasets to enumerate New Zealand's national and subnational flood hazard-exposure under temperature warming increments and Shared Socioeconomic Pathway (SSP) global emission scenarios between 2020 and 2090. At baseline 0°C, 753,656 people (17.9%), 555,942 buildings (NZD 235.1 billion), and 26,832 km of roads are exposed nationally, with three-waters infrastructure exhibiting substantially higher proportional exposure than population and buildings. Under +3°C warming, population and building hazard-exposure is proportionally highest in West Coast, Nelson, and Canterbury regions, with Hawke's Bay observing the largest warming-driven increases in hazard-exposure between 0°C and 3°C. The narrow difference in hazard-exposure observed between low- and high-emissions SSP scenarios by 2090 suggests urban growth and development location, rather than emissions trajectory, could be the primary determinants of future flood hazard-exposure. This finding has direct implications for national disaster risk management policy, reinforcing the importance of land-use planning and flood scheme management for limiting New Zealand's future flood hazard-exposure.