A national flood awareness system for ungauged catchments in complex topography: The case of development, communication and evaluation in New Zealand

Effectively forecasting and communicating flood hazards at national or continental scales is critical to reducing impacts of flooding. Yet, it remains a challenge due the predominance ungauged catchments in often complex steep terrain. We present development, communication, evaluation awareness system, Aotearoa (New Zealand) Flood Awareness System, AFAS. Forecasts are produced with an uncalibrated, semi-distributed hydrological model, driven by high-resolution convective-scale atmospheric model statistical perturbations rainfall, soil moisture baseflow generate 50-member ensemble. implement relative flow exceedance threshold framework evaluate hourly forecasts across six categories from below normal extremely high. Forecast performance categorically assessed against observations, for 2.5-year reforecast, 272 sites nationwide, up 48 h ahead. Overall, AFAS produces skilful streamflow topography, even operational delays ingesting observations. explore novel approach river forecast communication using daily videos. suggest rethinking large-scale balancing depth breadth (pointwise absolute flows versus distributed flows), raise collective before during natural disasters. appears be first system producing public-friendly videos communicate their topographical context. Future development will benefit federated regional agencies, including sharing real-time weather tools expertise.