Sediment connectivity evolution in three deglaciating Alpine catchments since the Little Ice Age: A graph-based reconstruction

Climate-driven glacier retreat is reorganizing sediment cascades across Alpine catchments. However, what remains poorly quantified is how their structural connectivity—the spatial configuration of landforms and pathways along which sediment can be transferred—evolves over deglaciation timescales. We reconstruct structural connectivity evolution in three glaciated catchments of the European Alps (i.e. Grastal, Kaunertal, Martelltal) over ~150 years since the Little Ice Age, using graph-based analysis of sediment cascade networks in which landforms are nodes and sediment pathways directed edges. Graphs were derived from multitemporal geomorphological maps combining historical maps, terrestrial photographs, Structure-from-Motion multi-view stereo (SfM-MVS) photogrammetry, and Airborne Laser Scanning (ALS)–derived DEMs, extending reconstruction to the 1870s–1890s. Despite similar deglaciation forcing, the three catchments followed divergent trajectories, with sources, links, and barriers evolving along site-specific rather than common paths. Changes were non-linear and episodic: glacier recession produced threshold-like reorganizations at Kaunertal and Grastal near the turn of the millennium, once retreating glaciers crossed topologically significant boundaries. Barrier positioning, not abundance, controlled system-scale filtering: a single strategically located lake in Grastal intercepted more sediment pathways than 13 lakes in Martelltal. Event-based routing showed connectivity increased in Kaunertal but declined in the other two via different mechanisms, indicating that network restructuring can outweigh source expansion in setting potential sediment delivery.