Regional flood hazard mapping for February 2023 Ex-Tropical Cyclone Gabrielle, New Zealand

Abstract. On February 13th to 14th 2023 ex-Tropical Cyclone Gabrielle (ETC Gabrielle) caused widespread flooding in Aotearoa New Zealand. The dataset presented is a collection of simulations representing the hydrodynamics response of 16 locations across the Hawke’s Bay and Tairāwhiti regional districts to ETC Gabrielle. Using gridded hourly rainfall derived from rainfall gauges, an end-to-end hydrodynamics modelling framework was applied to generate 16 inundation models with variable grid resolutions from 64 m to 4 m. The framework includes: (i) the identification of contributing river networks and catchments from an initial outline of the regions of interest, (ii) reconstruction of the DEM and surface roughness map, (iii) extraction of the rainfall, (iv) hydrological modelling in the upper catchments to estimate input river hydrographs, and (v) hydrodynamic modelling on the lower catchment. These models were calibrated and validated against hydrograph records (temporal accuracy), as well as post-event aerial imagery and in-situ high-water mark surveys (spatial accuracy) where available. With the increasing frequency of extreme weather events, this spatio-temporally detailed and methodologically consistent dataset offers valuable insights for researchers and stakeholders on the implications of large-scale flood events and will support efforts to enhance protective and preventive measures as well as post hoc analysis of direct and indirect impacts (e.g., building and infrastructure physical damage), while the model framework can be employed to simulate flood maps for future events. The dataset is available at https://doi.org/10.5281/zenodo.17986628 (Pelmard, 2025a) for the Tairāwhiti regional district and https://doi.org/10.5281/zenodo.18001575 (Pelmard, 2025b) for the Hawke’s Bay regional district.