Freeze‐Thaw Effects on Daily Sediment Transport in an Alpine River

Abstract Ongoing climate change and cryospheric degradation are intensifying sediment transport in cold mountain regions, leading to elevated sediment loads that adversely impact downstream areas. However, the influence of freeze‐thaw processes on daily catchment‐scale sediment transport in glaciated basins remains poorly understood. Here, we estimate the effect of freeze‐thaw processes on daily suspended sediment concentrations (SSC) in the Vent‐Rofental basin, Austria. Using Bayesian change‐point hierarchical regression, we assess the influence of streamflow, frozen ground extent (FGE), and diurnal freeze‐thaw cycles (FTCs) across three distinct freeze‐thaw states: thawing spring, thawed summer, and freezing autumn. While streamflow is the dominant driver of sediment transport, its effect is modulated by freeze‐thaw conditions and an interaction with temperature. FGE was found to reduce daily SSC, attributed to a reduction in the sediment contributing area. A discernible shift in suspended sediment dynamics is observed as the catchment transitions from frozen to thawed, marked by a change‐point when nearly all (97%) of the catchment is thawed. The thawed summer state exhibited the highest SSC due to elevated glacier melt. While the effect of diurnal FTCs on catchment‐scale fluvial sediment dynamics is ambiguous, a credible temperature‐adjusted effect in the thawing spring state may indicate enhanced sediment transport by amplifying snowmelt erosion. This study suggests that as glaciers retreat, snowmelt‐ and freeze‐thaw‐driven erosion, in addition to erosive rainfall, will become increasingly influential in determining sediment fluxes.