Articles | Volume 20, issue 12
Hydrol. Earth Syst. Sci., 20, 5015–5033, 2016
Hydrol. Earth Syst. Sci., 20, 5015–5033, 2016

Research article 19 Dec 2016

Research article | 19 Dec 2016

The importance of snowmelt spatiotemporal variability for isotope-based hydrograph separation in a high-elevation catchment

Jan Schmieder1, Florian Hanzer1, Thomas Marke1, Jakob Garvelmann2, Michael Warscher2, Harald Kunstmann2, and Ulrich Strasser1 Jan Schmieder et al.
  • 1Institute of Geography, University of Innsbruck, 6020 Innsbruck, Austria
  • 2Institute of Meteorology and Climate Research – Atmospheric Environmental Research, Karlsruhe Institute of Technology, 82467 Garmisch-Partenkirchen, Germany

Abstract. Seasonal snow cover is an important temporary water storage in high-elevation regions. Especially in remote areas, the available data are often insufficient to accurately quantify snowmelt contributions to streamflow. The limited knowledge about the spatiotemporal variability of the snowmelt isotopic composition, as well as pronounced spatial variation in snowmelt rates, leads to high uncertainties in applying the isotope-based hydrograph separation method. The stable isotopic signatures of snowmelt water samples collected during two spring 2014 snowmelt events at a north- and a south-facing slope were volume weighted with snowmelt rates derived from a distributed physics-based snow model in order to transfer the measured plot-scale isotopic composition of snowmelt to the catchment scale. The observed δ18O values and modeled snowmelt rates showed distinct inter- and intra-event variations, as well as marked differences between north- and south-facing slopes. Accounting for these differences, two-component isotopic hydrograph separation revealed snowmelt contributions to streamflow of 35 ± 3 and 75 ± 14 % for the early and peak melt season, respectively. These values differed from those determined by formerly used weighting methods (e.g., using observed plot-scale melt rates) or considering either the north- or south-facing slope by up to 5 and 15 %, respectively.

Short summary
We present novel research on the spatiotemporal variability of snowmelt isotopic content in a high-elevation catchment with complex terrain to improve the isotope-based hydrograph separation method. A modelling approach was used to weight the plot-scale snowmelt isotopic content with melt rates for the north- and south-facing slope. The investigations showed that it is important to sample at least north- and south-facing slopes, because of distinct isotopic differences between both slopes.