Rhine flood stories: Spatio-temporal analysis of historic and projected flood genesis in the Rhine River basin

The genesis of floods in large river basins often is complex. Streamflow originating from precipitation and snowmelt and different tributaries can superimpose and cause high water levels, threatening cities and communities along the riverbanks. For better understanding the mechanisms (origin and composition) of flood events in large and complex basins, we capture and share the story behind major historic and projected streamflow peaks in the Rhine River basin. Our analysis is based on hydrological simulations with the mesoscale Hydrological Model forced with both meteorological observations and an ensemble of climate projections. The spatio-temporal analysis of the flood events includes the assessment and mapping of antecedent liquid precipitation, snow cover changes, generated and routed runoff, areal extents of events, and the above-average runoff from major sub-basins up to 10 days before a streamflow peak. We introduce and assess the analytical setup by presenting the flood genesis of the two well-known Rhine floods that occurred in January 1995 and May 1999. We share our extensive collection of event-based Rhine River flood genesis, which can be used in- and outside the scientific community to explore the complexity and diversity of historic and projected flood genesis in the Rhine basin. An interactive web-based viewer provides easy access to all major historic and projected streamflow peaks at four locations along the Rhine. The comparison of peak flow genesis depending on different warming levels elucidates the role of changes in snow cover and precipitation characteristics in the (pre-)Alps for flood hazards along the entire channel of the Rhine. Furthermore, our results suggest a positive correlation between flood magnitudes and areal extents of an event. Further hydro-climatological research is required to improve the understanding of the climatic impact on the Rhine and beyond.