A multi-hazard framework integrating flood and landslide early warning systems: Application to the Tordera river basin (Catalonia, Spain)

Compounding and cascading effects of rainfall-induced floods and landslides pose significant challenges and existing research has predominantly focused on individual hazards and the multi-hazard aspect has been understudied. To bridge the gap, the current study develops a multi-hazard approach by building upon validated flood and landslide hazard assessment methods. The first steps in our approach involve determining the flood hazard in the river network and landslide warnings. With the landslide warnings denoting the initiation areas of the landslides, the warnings are combined with a morphological index to determine the potential sediment amount generated in subbasins and their connectivity to the drainage network. Finally, the multi-hazard aspect in the river network is obtained by integrating sediment transport and flood hazards. The results indicate the regions that have amplified hazards due to the combined effect of floods and sediment transport. An initial version of the proposed framework was tested in the Tordera River basin, with a focus on the Gloria storm that occurred in January 2020. This storm caused widespread floods and landslides across Catalonia (NE Spain), resulting in substantial damage. Choosing this area allowed us to see how well the framework works in understanding multi-hazard aspects. The results highlight the areas with the highest occurrence of landslides and also the regions in the drainage network where significant changes occurred due to floods and sediment transport. The identified areas match with regions where noticeable alterations were observed during the Gloria storm. The preliminary results showcase the capability of the framework to effectively capture the amplified hazard, providing valuable insights into the compounding and cascading effects of rainfall-induced floods and landslides.