Interaction between climatic conditions, water- and sediment-fluxes in an alpine basin: Long-term monthly and seasonal analysis

Abstract

Mountain basins are sites where complex interactions among climatic, geological, geomorphic, and ecological conditions can unfold. These interplays can be reflected in the erosion processes, and in the water and sediment fluxes released along the stream network, which can be highly variable in time and space. To investigate the relationships between temperature, precipitation, runoff, and sediment fluxes at monthly and seasonal scales in an Alpine basin, this work analyzed a long-term (January 1987–September 2018) field dataset produced in the Rio Cordon basin (eastern Italian Alps). The monthly variability revealed that higher precipitation occurred in summer (i.e., June–August). However, the runoff peaked in May generated by the snowmelt process. The total sediment load exhibited two peaks in May and September, somewhat reflecting the pattern of the monthly peak of water discharge. The monthly correlation analysis proved that temperature and precipitation weakly influenced the variables investigated, while the peak of water discharge was a good predictor of sediment fluxes observed. At the seasonal scale, temperature influenced snowmelt and summer dynamics, while precipitation showed the highest correlations in autumn. The hysteresis patterns obtained by the relationships between the averaged peak of water discharge and sediment loads (suspended load and bedload) highlighted the succession of high transport efficiency months and months characterized by supply-limited conditions. Such dynamics appeared strongly influenced by a single month, i.e., September 1994, when a large and infrequent flood affected the study basin. September 1994 resulted in a breakpoint in the mass curve built by relating cumulated runoff and cumulated total load, inducing a change in the long-term trend observed until then. Specifically, about 8 years of intensified sediment load were noted, a period during which the Rio Cordon experienced frequent streamed reworking and release of fine material. These findings demonstrated how alpine basins can respond to large and infrequent events, which can be expected more frequently due to climate change, providing important insights into areas such as soil erosion control, river basin management and hazard assessment.