Tracking sediment cascade evolution in Alpine catchments since the Little Ice Age: A graph-based approach integrating historical and modern data sources

Climate-driven glacier retreat is fundamentally restructuring sediment transfer systems in Alpine catchments, yet quantifying these changes over timescales relevant to global warming remains challenging. Established approaches to sediment connectivity assessment, such as DEM-based connectivity indices or sediment flux measurements, face limitations when applied across centennial timescales due to inconsistent data quality and sparse temporal or spatial coverage.

We present a graph-theoretic framework for analyzing structural sediment connectivity evolution across three glaciated catchments in the Central European Alps (Grastal, Kaunertal, Martelltal) over approximately 150 years since the Little Ice Age maximum. Our approach derives sediment cascade graphs from multitemporal geomorphological maps, using landforms as fundamental spatial units. The key methodological challenge lies in enabling meaningful comparisons across study sites of different sizes and configurations, and across time periods characterized by heterogeneous source data.

To achieve temporal depth, we integrate diverse data sources: historical topographic maps (1870s–1930s), georeferenced terrestrial photographs, aerial imagery processed with Structure-from-Motion photogrammetry (1940s–1990s), and recent ALS-derived products. Graph creation follows a semi-automatic workflow combining GIS-based flow routing with manual sediment source identification from DEMs of Difference and orthoimagery. We specifically address hydrological sediment connectivity, focusing on fluvial transport processes that dominate sediment export from glaciated systems.

We develop and apply graph metrics designed to be robust against variations in network size and data quality, enabling direct comparison of structural properties across catchments and time periods. These metrics characterize pathway architecture, the topological positioning of barrier landforms (lakes, braidplains, alluvial fans), and potential functional sediment connectivity under event-scale forcing through a simplified routing model.

Results indicate that the three catchments exhibit distinct evolutionary trajectories, with network structural changes and barrier formation capable of substantially modulating the response to deglaciation. The approach demonstrates that graph-based representations can be consistently derived from heterogeneous historical sources, offering a transferable methodology for investigating how sediment cascade structure mediates landscape response to climate forcing across decadal to centennial timescales.