Participatory Development of Storymaps to Illustrate the Spatiotemporal Dynamics and Impacts of Extreme Flood Events

Investments in flood protection are often made as a reaction to recent events. Flood risk communication and awareness creation might help to raise the motivation for preventive action in flood risk management, rather than implementing reactive measures after an event has occurred. In order to develop a way to convey scientific insight and data on flood risk, together with stakeholders, we are developing an interactive online tool to generate storymaps of local and national extreme flood events. To learn about the needs of every stakeholder, how flood risk information could be communicated and how practitioners can finally apply a resulting tool, we carried out an iterative co-development process. Stakeholders from local emergency intervention forces, insurance companies, cantonal and federal environment offices were interrogated in semi-structured interviews and workshops in an iterative process. The result is an online tool, which allows a user to construct storymaps of extreme flood events by varying several boundary conditions (e.g. duration of the precipitation event, initial conditions, etc.). These storymaps depict how a flood produced by physically plausible storylines of extreme precipitation events evolves and recedes.

With the development of storymaps, we connect physically plausible storylines with dynamical mapping. Both methods address the episodic memory and allow the user to connect new information to personal experiences or the collective memory, and hence create an emotional element. Storylines furthermore allow focusing on single possible realisations of an extreme event rather than an ensemble mean.

The storylines are constructed with the help of a comprehensive model chain: extreme precipitation events (return period >= 100 years) extracted from 8490 years of two merged hindcast archives of ECMWF – ENSext (1998-2017) and SEAS5 (1981-2017) – are used as scenarios to run a hydrological model for the main rivers and lakes in Switzerland. Subsequently, the results of the hydrologic simulations are fed into a hydrodynamic model coupled with an impact module to assess the flood impacts on buildings, roads, and critical facilities such as schools and retirement homes, including the number of affected people. The generated storymaps can be directly used in emergency intervention planning and training, because they provide dynamic information on possible flood impacts in contrast to static hazard maps, which are used for this purpose today. Furthermore, the tool might help to raise flood risk awareness among professionals as well as the interested public by visualizing and localizing physically consistent flood hazard information in an intuitive way.