SCoMHA: a framework to analyse process-level sediment connectivity in multi-hazard events

Abstract A slope saturated from prolonged rainfall suddenly fails and connects to the channel; while high runoff mobilizes loose sediments into a debris flow, a landslide supplies more material that clogs channels and floods areas downstream—a hazard-chain in motion. Multi-hazard events in mountains often involve such complex process-dynamics that are tied together by sediment connectivity. Yet, this important conduit is rarely accounted for in hazard analysis. This study addresses that gap by developing a new framework that integrates sediment connectivity into multi-hazard analysis in mountain catchments. It adopts a data-agnostic structure that incorporates both qualitative and quantitative data through a fuzzy logic scheme. This is then used to calculate a sediment connectivity weight (SCW) for each process comprising a multi-hazard event. Applying it to eight Alpine events reveals how proficiently each underlying process shapes the propagation and distribution of a hazard cascade. Sediment-heavy flows and severe channel erosions received high-SCW scores, indicating strong functional connectivity and a dominant role in event dynamics. Conversely, depositional processes or those reaching beyond the source-catchment score low, indicating gradual termination of the cascade. It also captures abrupt transitions like overtopped structures turning from barriers to connectors and disconnected areas being suddenly reactivated. Such patterns affirm that sediment connectivity is a dynamic catchment property continuously interacting with hazard processes—highlighting the need for holistic assessments. The modular and flexible design of the framework enables wide applicability and integration of additional indicators or logic to effectively analyse complex multi-hazard dynamics.