An Impacts-Based Flood Decision Support System for a Tropical Pacific Island Catchment with Short Warnings Lead Time

Abstract

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.

A Proposed Method for Calculating the Rainfall Threshold Based on the Multi-Method to Provide Heavy Rain Disaster Impact Information

“…Ref. [13] presented a case study on a pilot project that aimed to establish impact-based flood monitoring and an early warning and decision support system for the Vaisigano River, which flows through Apia, the capital of Samoa. Ref.…”

Flash Floods: Forecasting, Monitoring and Mitigation Strategies

“…The regionalization method can be also applied in the process-based modeling of flash floods. Williams et al [10] applied a rainfall regionalization method to construct flash flood hyetographs with several return periods using the flash flood shape of the historical event that occurred in the Tlalnepantla River basin, Mexico. A semi-distributed model in HEC-HMS was used to obtain the outflow hydrograph and hydrodynamic model in Iber, and Hec-Ras 2D to simulate free surface flow was used for a hydrological-hydrodynamic two-dimensional analysis.…”