A flood storyline tool to train first responders and civil protection forces

The Swiss first responders and civil protection agencies work with scenarios to train and prepare for high-impact weather events. These scenarios have traditionally been focusing on events with moderate severity (return periods of 30 to 100 years). After the flood event in the Ahr catchment in summer 2021 a need for more extreme and worst-case scenarios has been recognized.   The online-tool flood dynamics (https://flooddynamics.floodrisk.ch/) addresses these needs.

We have used the UNSEEN method, i.e. re-forecast archives from S2S ensemble predictions,  to identify nine scenarios (storylines) of very extreme precipitation accumulations over 3 to 5 days in Switzerland that serve as meteorological input for the tool. The precipitation storylines are processed through a chain of hydrological and hydraulic models to identify flooded areas. The flooded areas are then intersected with exposure data (buildings, roads, residents, critical infrastructure such as hospitals) to illustrate and quantify the impacts of the flooding. Impacts are quantified i) in monetary damages on buildings, ii) as number of affected persons, workplaces, hospitals, nursing homes, and schools, and iii) as the locations and length of impassable roadsections. 

A novel aspect of the tool is that it provides physically plausible, temporally evolving flood storylines. The evolution of the flooded areas is illustrated at an hourly time-resolution. Because this information includes both flooded buildings and flooded and hence impassable roads, first responders can for example see how access to critical infrastructure such as hospitals or to their own headquarters is interrupted during the events. The detailed visualizations in the form of maps and time evolutions available in the tool provide information far beyond classical training scenarios. The tool furthermore provides a regional overview on the (timing of) flood impacts over large parts of Switzerland. This large-scale perspective is relevant to prepare emergency organisations for extreme events, when many river sections are affected at the same time.