Communicating Ensemble Forecasts to Non-Experts: Reflection on a European Experience

Have you ever wondered how to effectively communicate the nature of ensemble forecasting? Are ensemble forecast products really used in practice and for real-life decision making? How are ensembles perceived by endusers and non-experts?

Ensemble driven decision making in areas such as wind-energy, shipping, forest-fires and hydrology is often advertised as the latest state-of-the-art technique. These applications are often situated in between the designer of EPS systems (thus are end-users of EPS) and their own stakeholders, which often include experts in different disciplines and non-experts. In this seminar we will concentrate on the experience of one particular enduser: operational flood forecasters.

Drawing on interviews and other research with operational flood forecasters from across Europe, this paper highlights a number of challenges to communicating and using ensemble flood forecasts operationally. We show how operational flood forecasters understand the skill, operational limitations, and informational value of EPS products in a variety of different and sometimes contradictory ways. Despite the efforts of forecasting agencies to design effective ways to communicate EPS forecasts to non-experts, operational flood forecasters were often skeptical about their ability to understand or use them appropriately. We argue that better training and closer contacts between operational flood forecasters and EPS system designers can help ensure the uncertainty represented by EPS forecasts is represented in ways that are most appropriate and meaningful for their intended consumers. But we also highlight some fundamental political and institutional challenges to using ensembles, such as differing attitudes to false alarms and to responsibility and blame in the event of blown or mistaken forecasts.

The scientific uncertainties about whether or not a flood will occur comprise only part of the wider 'decision' uncertainties faced by those charged with flood protection, who must also consider questions about how warnings they issue will subsequently be interpreted. By making those first order scientific uncertainties more explicit, ensemble forecasts can sometimes complicate, rather than clarify, the second order decision uncertainties they are supposed to inform.