Early warnings decision support systems are recognized as effective soft adaptation tools to prepare for the impacts of imminent flooding and minimize potential injuries and/or loss of life in flood-prone regions. This paper presents a case study of a pilot project that aimed to establish an impacts-based flood monitoring, early warnings, and decision support system for the Vaisigano River which flows through Apia, the capital of Samoa. This river is located in a characteristic short and steep catchment with rapid critical flood peak durations following periods of intense rainfall. The developed system integrates numerical weather prediction rainfall forecasts, real-time rainfall, river level and flow monitoring data, precomputed rainfall-runoff simulations, and flood inundation estimates of exposure levels and threat to human safety at buildings and on roads for different return period events. Information is ingested into a centralized real-time, web-based, flood decision support system portal that enables hydrometeorological officers to monitor, forecast and alert relevant emergency or humanitarian responders of imminent flooding with adequate lead time. This includes nowcasts and forecasts of estimated flood peak time, magnitude and likely impacts of inundation. The occurrence of three distinct extreme rainfall and flood events over the 2020/2021 tropical cyclone season provided a means to operationally test the system. In each case, the system proved adequate in alerting duty officers of imminent flooding in the Vaisigano catchment with up to 24 h warnings and response lead time. Gaps for improvement of system capabilities and performance are discussed, with recommendations for future work suggested.

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<p>The National Institute of Water and Atmospheric Research (NIWA) is mandated to research and develop tools to increase New Zealand’s resilience to environmental hazards, including floods. NIWA generates and delivers its bespoke past, present and future environmental information services via a platform called EcoConnect. Comprising forecast output from numerical models of meteorological, hydrological and hydrodynamical hazards and data from related observation platforms, EcoConnect specialises in the creation and delivery of information that increases awareness of a broad range of environmental conditions, and provides input for a variety of specialist decision-support tools, chief of which is a customisable user-interface called NIWA Forecast, that uses this information to mitigate environmental hazards and commercial risk.  EcoConnect operates 24 hours a day, 7 days a week and is fully supported by scientific and technical staff.</p><p>The EcoConnect workflow, which operates autonomously via the Cylc workflow meta-scheduler, begins with the data-assimilating New Zealand Limited Area Model (NZLAM) and New Zealand Convective-Scale Model (NZCSM) numerical weather prediction models.  These are based on the Met Office Unified Model, running with horizontal resolutions of 4.5km and 1.5km respectively over the full New Zealand, Tasman Sea and eastern Australia region (NZLAM) and just New Zealand and its coastal waters (NZCSM). These models provide input data for a hydrological river flow model, TopNet, based on the TopModel framework, that forecasts streamflow for just under 50,000 river reaches around New Zealand and a hierarchy of sea state and wave forecast models, based on the Wavewatch III model and locally called NZWAVE and NZTIDE. A coastal inundation model called RiCOM is also driven using data from the weather forecast models. Observation datasets provided within EcoConnect include satellite imagery, surface weather station data, river gauges and wave buoys. All of these data are created, collected, processed and archived by bespoke tasks in the EcoConnect workflow, all managed by Cylc. </p><p>Almost all users of forecast products have bespoke needs, such as operational decision-making, and hence it is important to be able to cater to specific client requirements. Through EcoConnect, fit-for-purpose warnings can be configured, based on a user’s operational requirements, for any of the data sources in EcoConnect. For example, if the forecasted wave, or streamflow discharge, at a specified location were to exceed a specific threshold, a client can be warned via customisable alerts within EcoConnect and thus react appropriately. A collection of standard products is generated within EcoConnect and tools within the primary user-interface are provided to interrogate the data and define custom “workspaces” that provide at-a-glance monitoring capabilities. </p><p>In this presentation, we will describe capabilities of the EcoConnect platform as they relate to hazard forecasting and warning. By means of a case study, we will show how EcoConnect was used to provide heads-up forecasting and decision-making support for an event that comprised weather, hydrological and wave hazards at the same time.  We will also highlight lessons learned and future development plans.</p>