Numerical Investigation of Sediment‐Yield Underestimation in Supply‐Limited Mountain Basins With Short Records

• Published in: Geophysical research letters 2022-04, Vol.49 (7), p.n/a
• Main Authors: Hirschberg, Jacob, McArdell, Brian W., Bennett, Georgina L., Molnar, Peter
• Format: Article
• Language: English
• Subjects: Catchment area; Climate change; Climatic extremes; Debris flow; debris flows; detrended fluctuation analysis; Downstream; environmental signals; Erosion rates; geomorphic record; Geomorphology; Interannual variability; Mathematical models; Mountains; Radiative forcing; Records; Sediment; Sediment discharge; Sediment yield; Sediments; stochastic modeling; Stochasticity; Storage; uncertainty; Uncertainty analysis; Weather; Weather effects
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL096440

Climate and sediment supply are critical for geomorphic systems. It is known that complex relations between such forcings and sediment mobilization may lead to dampened or erased environmental signals in sediment records. But it is unclear under which circumstances environmental signals are transmitted and measurable downstream. We used a numerical approach consisting of a sediment cascade model and a stochastic weather generator to quantify climate forcing effects under a range of sediment supply regimes in a debris‐flow catchment in the Swiss Alps (Illgraben). We show that sediment yields estimated from short records are highly uncertain both in terms of mean and interannual variability. Furthermore, sediment yields tend to be underestimated in supply‐limited systems, where also long‐term memory effects, driven by the history of sediment storage, are evident. Consequently, determining geomorphic system response from short records may be grossly inaccurate and should be extended with sediment supply detection and uncertainty analysis. Plain Language Summary Whether or not environmental signals, such as climate change or extreme events, are measurable in the sediment output of a basin is a timely question. Climate change affects processes related to sediment production and transport. However, because relations between these are complex, it is questionable if environmental signals are transmitted and measurable in the downstream sediment discharge. Here, we used a numerical approach for a geomorphic system; the Illgraben debris‐flow catchment in the Swiss Alps. We coupled a sediment cascade model and a stochastic weather generator to study the detectability of change in sediment yield under a range of conditions, such as different sampling durations and mean erosion rates. We show that sediment yields estimated from short records are highly uncertain and that the history of sediment supply and storage matters. These effects should be included in assessments of change in geomorphic systems. Key Points Long‐term sediment flux simulations (10k years) at hourly resolution are studied under stochastic climatic forcing Sediment yield estimates from short records (