Can sediment connectivity improve our understanding of multi-hazard events? A process-based perspective with SCIMA

Mountain catchments host tightly coupled erosion, transport, deposition, and feedback processes that often interact during multi-hazard events. Yet, these interactions are rarely analysed through sediment connectivity, despite it acting as a key vector linking hillslopes, channels, and downstream processes across space and time. This limits our ability to understand how event-driven sediment transfer governs hazard propagation in mountain landscapes.

We present SCIMA (Sediment Connectivity Indexed Multi-hazard Assessment), a process-based framework that embeds functional sediment connectivity into multi-hazard analysis. SCIMA dissects an event into process-level segments according to its spatio-temporal evolution and quantifies each segment’s contribution to sediment mobilisation, transfer, and deposition. Connectivity is expressed as a sediment connectivity weight (SCW) derived via a fuzzy-logic scheme that integrates heterogeneous information typical of mountain settings, including qualitative process interpretation (event reports and expert judgement) and quantitative geomorphic indicators (Melton ruggedness number and drainage density). This design is deliberately data-agnostic and modular, enabling transferability and extension with additional indicators where available.

We apply SCIMA to eight Alpine multi-hazard events in Austria and Switzerland involving combinations of mass movements, debris flows, channel erosion, and flooding. Results show that connectivity is highly variable within events and peaks during phases of intense sediment mobilisation and channel erosion, particularly where steep topography and direct process–process interactions dominate. Connectivity declines during depositional phases and in out-of-catchment segments, marking effective termination of the sediment cascade. Mitigation structures emerge as dynamic elements that can switch from buffering to amplifying connectivity when overtopped or failing. Overall, SCIMA demonstrates that sediment connectivity is an event-driven, dynamic property controlling erosion–transport feedbacks and multi-hazard evolution in mountain landscapes.