How different approaches to exposure and vulnerability inclusion affect Impact-based Forecasts and Warnings: Storm Eunice (2022) UK case study

The Met Office National Severe Weather Warning Service (NSWWS) has provided Impact-based Warnings to the public and local responders since 2011. These warnings aim to convey the likelihood of societal impacts resulting from adverse weather. The approach uses a warning impact matrix that categorises impact severity (very low, low, medium and high) and likelihood to assign a warning colour classification (yellow, amber and red). To assess impact severity effectively, consideration of the spatial and temporal variability of exposure and vulnerability is necessary. Different approaches are currently used to integrate this information in risk and impact-based warnings (e.g. Impact tables developed through engagement with the responder communities; expert judgement and engagement with local advisors; quantitative vulnerability and exposure indicators included within automated risk forecasting tools).

Using Storm Eunice as a case study, we explore how different methods of quantifying and integrating exposure and vulnerability could influence warning classification. Storm Eunice impacted the UK in February 2022 and led to the issuance of two rare, red wind warnings. Focusing on building damage, which is referred to as structural damage in the Met Office impact tables, and population affected, we review different approaches to warning generation using a: (1) hazard-only approach; (2) exposure-based approach; and (3) a risk-based approach (inclusive of vulnerability) and compare the possible warnings these different methods could produce. Using these results, we then reflect on the influence these differences have on warning recipients and the effect this might have on warning communication and actions taken.  We will leverage results from a recent Warning Value Chain Assessment of Storm Eunice to reflect on the uptake and responses to different warnings.