Linking heavy rainfall to suspended sediment fluxes in a deglaciating Alpine catchment

Abstract. Sediment transport in high-Alpine environments is undergoing a fundamental shift as glaciers retreat and heavy precipitation events become more frequent. Understanding how these changes influence suspended sediment yields (SSY) is critical for predicting future sediment dynamics, water quality, and geomorphic evolution in mountain catchments. This study investigates the role of heavy precipitation in driving suspended sediment export in the rapidly deglaciating, nested Alpine catchments of Tumpen-Ötztal and Vent-Rofental in Austria. We examine how precipitation and rainfall intensity, frequency, and duration influence suspended sediment yields and concentrations. Using a 21-year dataset of hourly 1 km gridded precipitation and a multi-scale detection approach, we identify heavy precipitation events and analyse their characteristics and contribution to sediment transport. Events are classified based on their temporal characteristics, distinguishing between sub-daily and long-duration heavy precipitation events, and spatial scale, distinguishing between catchment-wide and localised heavy precipitation. We also evaluate the influence of precipitation uncertainties. Our findings show a significant increase in the frequency of heavy precipitation events and their contribution to annual SSY. Sub-daily events, primarily convective summer storms, generate disproportionately high sediment fluxes due to their localised and intense rainfall. Sediment transport during long-duration events responds more strongly to increases in event rainfall intensity and totals. Despite an increasing trend in heavy-precipitation-driven sediment fluxes, annual SSY remains stable in Tumpen-Ötztal but declines in Vent-Rofental, suggesting that heavy-precipitation-driven transport may partially offset, but not fully replace, glacier-driven sediment supply. As climate projections indicate a continued rise in heavy precipitation, particularly at sub-daily scales, Alpine catchments may develop increasingly flashier sediment regimes in the future. However, long-term reductions in glacier-driven sediment supply will likely lead to overall declining annual sediment yields. These findings highlight the need for continued monitoring and study of changing precipitation dynamics, sediment transport, and paraglacial landscape evolution in high-Alpine environments.