Decadal-scale changes in sediment export from an Alpine proglacial area linked to an increasing frequency of rainfall extremes: evidence for an emerging sediment-export regime shift?

Climate change is strongly affecting sediment dynamics in the highly sensitive proglacial areas of high-mountain environments, as accelerated glacier melt and permafrost degradation expose new surfaces to erosion, while changing precipitation patterns influence erosion rates and sediment transport. Quantifying these changes is crucial for assessing geomorphological evolution, anticipating natural hazards, and evaluating the responses of both proglacial and downstream ecosystems. However, this task remains challenging as sediment yields from these landscapes are governed by complex interactions among moraine activity, glacial erosion, paraglacial adjustment, and channel morphology, with ongoing climate change further modulating the timing and magnitude of these processes.

This study aims to quantify temporal changes in sediment fluxes in the Sulden proglacial area in South Tyrol, Eastern Italian Alps, from 2005 to 2025, and to assess the role of climate variability in driving these changes. We used high-resolution digital elevation models (DEMs) from 2005, 2017, 2021, 2023, and 2025 to compute multi-temporal DEMs of Difference (DoDs) and derive mean annual sediment fluxes for each interval. Unequal interval lengths can bias flux estimates because short-lived peaks associated with extreme precipitation events may be averaged out over long periods. To address this, we calculated mean annual sediment flux over cumulative intervals starting in 2005 (2005-2017, 2005-2021, 2005-2023, and 2005-2025), providing a framework to evaluate whether, and to what extent, recent changes in precipitation patterns influence longer-term mean flux estimates. 

Our results show that mean sediment fluxes, referenced to 2005, have increased sharply and nonlinearly over time, spanning more than one order of magnitude by 2025 and revealing a clear acceleration relative to the 2005-2017 baseline. Comparison of the non-overlapping intervals 2005-2017 and 2017-2025 further emphasizes this shift, with mean fluxes during 2017-2025 approximately 40 times higher than during 2005-2017, indicating a fundamental increase in sediment export efficiency rather than short-term variability around a stable long-term mean. Interestingly, periods with similar amounts of erosion reveal contrasting amounts of deposition along low-slope fluvial pathways within the proglacial system, illustrating how functional connectivity controls sediment storage and ultimately sediment export. Precipitation records indicate an increase in the frequency of high-magnitude rainfall events after 2017, including more frequent exceedances of daily extremes and events approaching or exceeding a 10-year return period.

Together, these findings suggest that the increasing frequency of extreme precipitation events is a key driver of enhanced sediment yields in proglacial environments, with important implications for sediment-related hazards and associated management costs.