Coupling Climate Conditions, Sediment Sources and Sediment Transport in an Alpine Basin

In a fluvial system, mountain basins control sediment export to the lowland rivers. Hence, analysis of erosion processes and sediment delivery patterns in mountain basins is a key factor for many applications such as land-use management, hazard assessment and infrastructure design. Several studies have investigated the alterations triggered by recent climatic change on the hydrological regime, while only a few works have explored the consequences on fluvial sediment dynamics. Here, we combined and analyzed the quasi-unique dataset of climatic conditions, landform response and sediment export produced, since 1986 in the Rio Cordon basin (5 km2, Eastern Italian Alps) to examine the sediment delivery processes occurring in the last 3 decades. The temperature, precipitation and fluvial sediment fluxes in the basin were analyzed using continuous measurement executed by a permanent monitoring station, while the evolution of sediment source areas was investigated using three sediment source inventories. The results showed that during the period 1986-1993 the sediment fluxes (339 Mg yr-1) reflected the stable trend of the climatic conditions. The period between the first and second source inventory (i.e. 1994-2006) was characterized by climatic fluctuations and by the occurrence of high magnitude floods. Nevertheless, a limited increase in the extent of sediment source areas was detected, suggesting that the increased sediment export (759 Mg yr-1) was mainly driven by in-channel sediment supply. Notwithstanding the marked climate warming and the increased precipitation, a weak source area evolution and a reduction in sediment export (237 Mg yr-1) were observed during the period 2007-2015. In particular, the higher rainfall did not result in an intensification of flood events, stressing the absence of hillslope-channel connectivity.