Preprints
https://doi.org/10.5194/egusphere-2022-616
https://doi.org/10.5194/egusphere-2022-616
29 Aug 2022
 | 29 Aug 2022

Reconstructing five decades of sediment export from two glaciated high-alpine catchments in Tyrol, Austria, using nonparametric regression

Lena Katharina Schmidt, Till Francke, Peter Martin Grosse, Christoph Mayer, and Axel Bronstert

Abstract. To date, knowledge on the effects of decadal-scale changes in climatic forcing on sediment export from glaciated high alpine areas is still limited. This is primarily due to the extreme scarcity of sufficiently long records of suspended sediment concentrations (SSC), which precludes robust explorations of longer-term developments. Aggravatingly, insights are not necessarily transferable from one catchment to another, as sediment export can heavily depend on local preconditions (such as geology or connectivity). However, gaining a better understanding of past sediment export is an essential step towards estimating future changes, which will affect downstream hydropower production, flood hazard, water quality and aquatic habitats.

Here we test the feasibility of reconstructing decadal-scale sediment export from short-term records of SSC and long time series of the most important hydro-climatic predictors, discharge, precipitation and air temperature (QPT). Specifically, we test Quantile Regression Forest (QRF), a non-parametric, multivariate approach based on Random Forests. We train independent models for the two nested and partially glaciated catchments Vent (98 km2) and Vernagt (11.4 km2) in the Upper Ötztal in Tyrol, Austria (1891 to 3772 m a.s.l.), to gain a comprehensive overview of sediment dynamics. In Vent, daily QPT records are available since 1967, alongside 15 years of SSC measurements. At gauge Vernagt, QPT records started in 1975 in hourly resolution, which allows comparing model performances in hourly and daily resolution (Validation A). Challengingly, only four years of SSC measurements exits at gauge Vernagt, yet consisting of two 2-year datasets, that are almost 20 years apart, which provides an excellent opportunity for validating the model’s ability to reconstruct past sediment dynamics (Validation B).

As a second objective, we aim to assess changes in sediment export by analyzing the reconstructed time series for trends (using Mann-Kendall test and Sen’s slope estimator) and step-like changes (using two complementary change point detection methods, the widely used Pettitt’s test and a Bayesian approach implemented in the R package ‘mcp’).

Our findings demonstrate that QRF performs well in reconstructing past daily sediment export (Nash-Sutcliffe efficiency of 0.73) as well as the derived annual sediment yields (Validation B), despite the small training dataset. Further, our analyses indicate that the loss of model skill in daily as compared to hourly resolution is small (Validation A). We find significant positive trends in the reconstructed annual suspended sediment yields at both gauges, with distinct step-like increases around 1981. This coincides with a crucial point in glacier melt dynamics: we find co-occurring change points in annual and summer mass balances of the two largest glaciers in the Vent catchment. This is also reflected in a coinciding step-like increase in discharge at both gauges as well as a considerable increase in the accumulation area ratio of the Vernagtferner glacier. We identify exceptionally high July temperatures in 1982 and 1983 as a likely cause, as July is the most crucial month with respect to firn and ice melt. In contrast, we did not find coinciding change points in precipitation.

This study demonstrates that the presented QRF approach is a promising tool with the ability to deepen our understanding of the response of high-alpine areas to decadal climate change. This in turn will aid estimating future changes and preparing management or adaptation strategies.

Journal article(s) based on this preprint

11 May 2023
Reconstructing five decades of sediment export from two glacierized high-alpine catchments in Tyrol, Austria, using nonparametric regression
Lena Katharina Schmidt, Till Francke, Peter Martin Grosse, Christoph Mayer, and Axel Bronstert
Hydrol. Earth Syst. Sci., 27, 1841–1863, https://doi.org/10.5194/hess-27-1841-2023,https://doi.org/10.5194/hess-27-1841-2023, 2023
Short summary

Lena Katharina Schmidt et al.

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-616', Anonymous Referee #1, 04 Oct 2022
    • AC1: 'Reply on RC1', Lena Katharina Schmidt, 14 Dec 2022
  • RC2: 'Comment on egusphere-2022-616', Anonymous Referee #2, 18 Nov 2022
    • AC2: 'Reply on RC2', Lena Katharina Schmidt, 14 Dec 2022
  • RC3: 'Comment on egusphere-2022-616', Anonymous Referee #3, 21 Nov 2022
    • AC3: 'Reply on RC3', Lena Katharina Schmidt, 14 Dec 2022

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-616', Anonymous Referee #1, 04 Oct 2022
    • AC1: 'Reply on RC1', Lena Katharina Schmidt, 14 Dec 2022
  • RC2: 'Comment on egusphere-2022-616', Anonymous Referee #2, 18 Nov 2022
    • AC2: 'Reply on RC2', Lena Katharina Schmidt, 14 Dec 2022
  • RC3: 'Comment on egusphere-2022-616', Anonymous Referee #3, 21 Nov 2022
    • AC3: 'Reply on RC3', Lena Katharina Schmidt, 14 Dec 2022

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
ED: Reconsider after major revisions (further review by editor and referees) (28 Dec 2022) by Roberto Greco
AR by Lena Katharina Schmidt on behalf of the Authors (08 Feb 2023)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (08 Feb 2023) by Roberto Greco
RR by Dongfeng Li (18 Feb 2023)
RR by Anonymous Referee #1 (12 Mar 2023)
RR by Anna Costa (31 Mar 2023)
ED: Publish as is (12 Apr 2023) by Roberto Greco
AR by Lena Katharina Schmidt on behalf of the Authors (19 Apr 2023)

Journal article(s) based on this preprint

11 May 2023
Reconstructing five decades of sediment export from two glacierized high-alpine catchments in Tyrol, Austria, using nonparametric regression
Lena Katharina Schmidt, Till Francke, Peter Martin Grosse, Christoph Mayer, and Axel Bronstert
Hydrol. Earth Syst. Sci., 27, 1841–1863, https://doi.org/10.5194/hess-27-1841-2023,https://doi.org/10.5194/hess-27-1841-2023, 2023
Short summary

Lena Katharina Schmidt et al.

Model code and software

A Quantile Regression Forests approach for sedigraph-reconstruction and sediment yield calculation Lena Katharina Schmidt, Peter Martin Grosse, Till Francke http://doi.org/10.23728/b2share.109960a9fb42427b9d0a85b998b9d18c

Lena Katharina Schmidt et al.

Viewed

Total article views: 497 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
344 137 16 497 5 4
  • HTML: 344
  • PDF: 137
  • XML: 16
  • Total: 497
  • BibTeX: 5
  • EndNote: 4
Views and downloads (calculated since 29 Aug 2022)
Cumulative views and downloads (calculated since 29 Aug 2022)

Viewed (geographical distribution)

Total article views: 475 (including HTML, PDF, and XML) Thereof 475 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 11 May 2023
Download

The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Short summary
We present a suitable method to reconstruct sediment export from decadal records of hydro-climatic predictors (discharge, precipitation, temperature) and shorter suspended sediment measurements. This allows to fill the knowledge gap on how sediment export from glaciated high alpine areas has responded to climate change. We find positive trends in sediment export from the two investigated nested catchments, with step-like increases around 1981 which are linked to crucial changes in glacier melt.