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@ARTICLE{Stockinger:866434,
      author       = {Stockinger, Michael Paul and Bogena, Heye and Lücke,
                      Andreas and Stumpp, Christine and Vereecken, Harry},
      title        = {{T}ime variability and uncertainty in the fraction of young
                      water in a small headwater catchment},
      journal      = {Hydrology and earth system sciences},
      volume       = {23},
      number       = {10},
      issn         = {1607-7938},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2019-05575},
      pages        = {4333 - 4347},
      year         = {2019},
      abstract     = {The time precipitation needs to travel through a catchment
                      to its outlet is an important descriptor of a catchment's
                      susceptibility to pollutant contamination, nutrient loss,
                      and hydrological functioning. The fast component of total
                      water flow can be estimated by the fraction of young water
                      (Fyw), which is the percentage of streamflow younger than 3
                      months. Fyw is calculated by comparing the amplitudes of
                      sine waves fitted to seasonal precipitation and streamflow
                      tracer signals. This is usually done for the complete tracer
                      time series available, neglecting annual differences in the
                      amplitudes of longer time series. Considering inter-annual
                      amplitude differences, we employed a moving time window of 1
                      year in weekly time steps over a 4.5-year δ18O tracer time
                      series to calculate 189 Fyw estimates and their uncertainty.
                      They were then tested against the following null hypotheses:
                      (1) at least $90 \%$ of Fyw results do not deviate more
                      than ±0.04 $(4 \%)$ from the mean of all Fyw results,
                      indicating long-term invariance. Larger deviations would
                      indicate changes in the relative contribution of different
                      flow paths; (2) for any 4-week window, Fyw does not change
                      more than ±0.04, indicating short-term invariance. Larger
                      deviations would indicate a high sensitivity of Fyw to a
                      1-week to 4-week shift in the start of a 1-year sampling
                      campaign; (3) the Fyw results of 1-year sampling campaigns
                      started in a given calendar month do not change more than
                      ±0.04, indicating seasonal invariance. In our study, all
                      three null hypotheses were rejected. Thus, the Fyw results
                      were time-variable, showed variability in the chosen
                      sampling time, and had no pronounced seasonality. We
                      furthermore found evidence that the 2015 European heat wave
                      and including two winters into a 1-year sampling campaign
                      increased the uncertainty of Fyw. Based on an increase in
                      Fyw uncertainty when the mean adjusted R2 was below 0.2, we
                      recommend further investigations into the dependence of Fyw
                      and its uncertainty to goodness-of-fit measures.
                      Furthermore, while investigated individual meteorological
                      factors did not sufficiently explain variations of Fyw, the
                      runoff coefficient showed a moderate negative correlation of
                      r=−0.50 with Fyw. The results of this study suggest that
                      care must be taken when comparing Fyw of catchments that
                      were based on different calculation periods and that the
                      influence of extreme events and snow must be considered.},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {255 - Terrestrial Systems: From Observation to Prediction
                      (POF3-255)},
      pid          = {G:(DE-HGF)POF3-255},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000492837100003},
      doi          = {10.5194/hess-23-4333-2019},
      url          = {https://juser.fz-juelich.de/record/866434},
}