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Uncertainty information in natural hazard forecasts is increasingly being communicated explicitly. This study was designed to determine whether different ways of communicating uncertainty graphically affects the decisions and interpretations of forecasts and if expertise was a factor in the decisions and interpretations from forecasts explicitly showing uncertainty. In a hypothetical decision‐making task regarding ice thickness and shipping, 138 experts and non‐experts received ice‐thickness forecasts in four different presentations expressing uncertainty: worded probability, spaghetti plot, fan plot and box plot. These forecasts contained no measures of central tendency. There was no consistent difference in decision or best‐guess forecast (deterministic ice thickness forecast based on the forecast representation) between the different forecast representations. However, participants interpreted different amounts of uncertainty across the different forecast representations. Experts made significantly more economically rational decisions than non‐experts, interpreted lower best‐guess forecasts and inferred significantly more uncertainty than non‐experts. These results suggest that care be taken in choosing how uncertainty is represented in forecasts, especially between expert and non‐expert audiences.

During volcanic eruptions, Volcanic Ash Advisory Centres issue ash advisories for aviation showing the forecasted outermost extent of the ash cloud. During the 2010 Icelandic volcano Eyjafjallajökull eruption, the Met Office produced supplementary forecasts of quantitative ash concentration, due to demand from airlines. Additionally, satellite retrievals of estimated volcanic ash concentration are now available. To test how these additional graphical representations of volcanic ash affect flight decisions, whether users infer uncertainty in graphical forecasts of volcanic ash, and how decisions are made when given conflicting forecasts, a survey was conducted of 25 delegates representing U.K. research and airline operations dealing with volcanic ash. Respondents were more risk seeking with safer flight paths and risk averse with riskier flight paths when given location and concentration forecasts compared to when given only the outermost extent of the ash. Respondents representing operations were more risk seeking than respondents representing research. Additionally, most respondents’ hand-drawn no-fly zones were larger than the areas of unsafe ash concentrations in the forecasts. This conservatism implies that respondents inferred uncertainty from the volcanic ash concentration forecasts. When given conflicting forecasts, respondents became more conservative than when given a single forecast. The respondents were also more risk seeking with high-risk flight paths and more risk averse with low-risk flight paths when given conflicting forecasts than when given a single forecast. The results show that concentration forecasts seem to reduce flight cancellations while maintaining safety. Open discussions with the respondents suggested that definitions of uncertainty may differ between research and operations.

ABSTRACT:In the last decade, the growth of local, site-specific weather forecasts delivered by mobile phone or website represents arguably the fastest change in forecast consumption since the beginning of television weather forecasts 60 years ago. In the present study, a street-interception survey of 274 members of the public a clear first preference for narrow weather forecasts above traditional broad weather forecasts is shown for the first time, with a clear bias towards this preference for users under 40 years. The impact of this change on the understanding of forecast probability and intensity information is explored. While the correct interpretation of the statement 'There is a 30% chance of rain tomorrow' is still low in the cohort, in common with previous studies, a clear impact of age and educational attainment on understanding is shown, with those under 40 and educated to degree level or above more likely to correctly interpret it. The interpretation of rainfall intensity descriptors ('light', 'moderate' and 'heavy') by the cohort is shown to be significantly different to official and expert assessment of the same descriptors and to have large variance amongst the cohort. However, despite these key uncertainties, members of the cohort generally seem to make appropriate decisions about rainfall forecasts. There is some evidence that the decisions made are different depending on the communication format used, and the cohort expressed a clear preference for tabular over graphical weather forecast presentation.