Operational forecast uncertainty assessment for better information to stakeholders and crisis managers

¹ DREAL Centre-Val de Loire, Loire – Cher – Indre Flood Forecasting Centre, 45 064 Orléans cedex 2, France
² MEDDE, Service central d’Hydrométéorologie et d’Appui à la Prévision des Inondations, 31 057 Toulouse cedex 1, France
³ IFSTTAR, Geotechnics Environment and Risks department, 44 344 Bouguenais cedex 1, France
⁴ Météo-France, CNRM-GAME, 31 057 Toulouse cedex 1, France

^a Corresponding author: lionel.berthet@developpement-durable.gouv.fr

Abstract

Flood forecasting uncertainty is crucial information for decision makers. However, deterministic only forecasts have been communicated in France until now, like in many other countries. The French Flood Forecast Centres (FFCs) recently set up a new service which aims at publishing quantitative forecasts along with their associated uncertainty. Two surveys (one of the greater audience and identified end-users, another of FFCs worldwide) were conducted to design it. The forecasters' toolbox was then supplemented with two new tools. The first one provides automatic forecasting uncertainty estimations calibrated on past forecasting error series. The second one allows the forecasters to incorporate their own expertise to adjust the automatically calculated uncertainty estimation. The evaluation of the forecast uncertainty estimations issued in real time in 2014 suggests that even if these assessments are perfectible, they are already informative and useful for end-users. The first feedbacks from forecasters and crisis managers also show that if the assessment of probabilistic forecasts remains a technical challenge, their use is foremost a human challenge. This move is a paradigm change for both forecasters and decision makers. Therefore, they have to be accompanied in order to achieve this deep shift in their professional practice.