Impact-Based Forecasting and Warning

Ensemble and deterministic flow forecasts provide information to support routine operations and issuing early warnings in a range of applications, including floods, droughts and pollution incidents. However, to be operationally useful, forecasts need to be presented in terms which are meaningful to the end user and delivered in time to take effective action. Warning dissemination techniques include radio, television, social media, websites, sirens, smartphone apps and cell broadcasting. Decision-making tools which are used as part of this process include thresholds, decision support systems and risk-based techniques, using probabilistic forecasts. This chapter describes the background to these approaches and provides examples for a range of flood warning, reservoir and other applications. Examples include early warning dissemination systems from the USA and Bangladesh.