Preparing for the unprecedented

In an era of climate change, extremes relative to the historical record are expected to occur more frequently. In 2021, several weather disasters occurred in which conditions surpassed recorded extremes. These included floods and associated impacts in the USA, Europe, China and Indonesia, heat waves and wildfires in southern Europe and northwestern North America, and winter weather in Spain and the southern USA. Analysis of the performance of warning systems in these disasters by the WWRP HIWeather project shows that in most, but not all, cases there was adequate forewarning of the nature and magnitude of the event, but that lack of preparedness and/or communication failures led to loss of life in particular vulnerable groups.  Using information gathered for the HIWeather value chain database, I will present an overview of key aspects of each event – the weather and its impact, the forecasts, the warnings, and the responses. In the flood cases, a common feature was that limitations in the spatial resolution of the forecasts limited the ability of hydrological prediction systems to translate the rainfall forecast into a realistic flood forecast. In the case of the winter weather and heat waves, a lack of preparedness at both official levels and in the at-risk population led to failures of response. A comparative analysis of warning performance shows that communication failures were often distributed along the warning chain. Drawing on material from our recently published book, Towards the Perfect Weather Warning, I will draw some conclusions about critical components that are necessary for a successful warning system.