Storylines of the impacts in the Netherlands of alternative realizations of the Western Europe July 2021 floods

The 2021 summer flooding was an extremely rare event, driven by precipitation extremes that exceed Dutch design levels for flood protection in regions away from the main rivers and coastline. However, similar events in neighboring locations cannot be ruled out even in the near future. The implications of such extreme rainfall amounts will vary by region, subject to local topography, hydraulic flow patterns, water management, and societal exposure. We explore the geographic distribution of potential flood impacts induced by a similar event by constructing impact-oriented event storylines for different subregions in the Netherlands. The plausibility of the storylines is underlined by using physical evidence, proven impact-modelling concepts, and expert judgment successfully assessing the (sometimes unexpected) outcomes. The approach supports impact assessment for extraordinary events.

The presentation will illustrate the development of the storylines, and its uptake and interpretation by governing authorities responsible for water safety, civil protection and water management.