Identifying run-off contributions during melt-induced run-off events in a glacierized alpine catchment

We analysed contributions to run-off using hourly stream water samples from seven individual melt-induced run-off events (plus one rainfall event) during 2011, 2012 and 2013 in two nested glacierized catchments in the Eastern Italian Alps. Electrical conductivity and stable isotopes of water were used for mixing analysis and two-component and three-component hydrograph separation. High-elevation snowmelt, glacier melt and autumn groundwater were identified as major end-members. Discharge and tracers in the stream followed the diurnal variations of air temperature but markedly reacted to rainfall inputs. Hysteresis patterns between discharge and electrical conductivity during the melt-induced run-off events revealed contrasting loop directions at the two monitored stream sections. Snowmelt contribution to run-off was highest in June and July (up to 33%), whereas the maximum contribution of glacier melt was reached in August (up to 65%). The maximum groundwater and rainfall contributions were 62% and 11%, respectively. Run-off events were generally characterized by decreasing snowmelt and increasing glacier melt fractions from the beginning to the end of the summer 2012, while run-off events in 2013 showed less variable snowmelt and lower glacier melt contributions than in 2012. The results provided essential insights into the complex dynamics of melt-induced run-off events and may be of further use in the context of water resource management in alpine catchments.