Value added by hazard impact modelling within the warning value chain for three impactful surface water flooding events in 2022

The warning value chain is a concept whereby the process of producing a warning is represented by a chain of sources of expertise (components), connected by bridges that convey bidirectional information exchanges. An associated warning value chain questionnaire – produced by the WMO’s High Impact Weather (HIWeather) Warning Value Chain Flagship Project – has been used to carry out a warning value chain assessment for three surface water flooding (SWF) events in the UK. These events occurred during the summer and autumn of 2022 and involved localised convection leading to predominantly minor SWF impacts. Forecast confidence was very low for all events resulting in some short-lead time and responsive warnings. This talk will briefly describe these events before focusing on the value added to the warnings by the Surface Water Flooding Hazard Impact Model (SWFHIM). SWFHIM is an operational forecasting tool used by the Flood Forecasting Centre (a partnership between the Met Office and Environment Agency) to objectively assess the likelihood of SWF impacts across England and Wales, which ultimately feeds into the decision-making process for issuing warnings. The SWFHIM adds value to the weather and hazard outputs by deriving probabilities of impacts using a range of post-processing and forecast presentation methods. However, results from the warning value chain questionnaire helped to identify improvements that may enhance future warnings. For example, SWFHIM forecast presentation changes may improve the pull-through and interpretation of information. Also, recent enhancements to the configuration of the driving convective-scale ensemble are not yet being fully utilized by the hazard-impact modelling. These points and more will be discussed in this talk.