Importance of Two-way Communication with Users for Effective Utilization of Ensemble Flood Forecast Information

Abstract

Ensemble flood forecasts have a long lead time and provide probabilistic information. They are expected to be used for early hazard warnings. However, know-how for effective use of the information delivered from ensemble flood forecasts has not been established because ensemble flood forecasts have different characteristics from those of conventional deterministic flood forecasts. This study analyzed how communication between forecasters and users improved the operation of ensemble flood forecasting systems by surveying antecedent cases in overseas countries. Effective visualization of forecasting is an important process to deliver actionable information to users. We classified visualization techniques of ensemble flood forecasts into four categories and discussed the characteristics and expected usage of the respective visualization techniques. Results indicated that ideas for handling forecast uncertainties were included in visualization techniques to support users’ decision making by fully utilizing information taken from ensemble forecasts for issuing appropriate flood alerts. This can be done by converting a simulated discharge to an equivalent return period to avoid system bias issues or showing consistency of estimated risks with recent forecast results. Results also show that feedback from users collected through workshops can improve the operation of the flood forecasting systems. This user feedback helped to issue “very low likelihood but severe impact" alerts effectively and to reveal users’ capacity limitations because of an insufficient legal framework. We concluded that two-way communication between forecasters and users is necessary for effective flood forecast operation and for technical development.