‘Teflon Basin’ or Not? A High-Elevation Catchment Transit Time Modeling Approach

oleh: Jan Schmieder, Stefan Seeger, Markus Weiler, Ulrich Strasser

Format: Article
Diterbitkan: MDPI AG 2019-10-01

Deskripsi

We determined the streamflow transit time and the subsurface water storage volume in the glacierized high-elevation catchment of the Rofenache (Oetztal Alps, Austria) with the lumped parameter transit time model TRANSEP. Therefore we enhanced the surface energy-balance model ESCIMO to simulate the ice melt, snowmelt and rain input to the catchment and associated &#948;<sup>18</sup>O values for 100 m elevation bands. We then optimized TRANSEP with streamflow volume and &#948;<sup>18</sup>O for a four-year period with input data from the modified version of ESCIMO at a daily resolution. The median of the 100 best TRANSEP runs revealed a catchment mean transit time of 9.5 years and a mobile storage of 13,846 mm. The interquartile ranges of the best 100 runs were large for both, the mean transit time (8.2&#8722;10.5 years) and the mobile storage (11,975&#8722;15,382 mm). The young water fraction estimated with the sinusoidal amplitude ratio of input and output &#948;<sup>18</sup>O values and delayed input of snow and ice melt was 47%. Our results indicate that streamflow is dominated by the release of water younger than 56 days. However, tracers also revealed a large water volume in the subsurface with a long transit time resulting to a strongly delayed exchange with streamflow and hence also to a certain portion of relatively old water: The median of the best 100 TRANSEP runs for streamflow fraction older than five years is 28%.