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@ARTICLE{Huang:875091,
      author       = {Huang, Yafei and Hendricks-Franssen, Harrie-Jan and Herbst,
                      Michael and Hirschi, Martin and Michel, Dominik and
                      Seneviratne, Sonia I. and Teuling, Adriaan J. and Vogt,
                      Roland and Detlef, Schumacher and Pütz, Thomas and
                      Vereecken, Harry},
      title        = {{E}valuation of different methods for gap filling of
                      long‐term actual evapotranspiration time series measured
                      by lysimeters},
      journal      = {Vadose zone journal},
      volume       = {19},
      number       = {1},
      issn         = {1539-1663},
      address      = {Alexandria, Va.},
      publisher    = {GeoScienceWorld},
      reportid     = {FZJ-2020-01798},
      pages        = {1-15},
      year         = {2020},
      abstract     = {Terrestrial evapotranspiration (ET) is the second largest
                      water flux in the global water cycle. It can be measured
                      with different techniques; weighable lysimeters can provide
                      very accurate measurements, and some very long‐term time
                      series exist. However, these lysimeter time series are
                      affected by data gaps that must be filled to estimate actual
                      ET totals and long‐term trends. In this paper, we explore
                      four different gap‐filling methods: the potential
                      ET‐method, the ratio method, the FAO‐based water balance
                      method, and HYDRUS modeling. These gap‐filling methods
                      were evaluated for three time series of actual ET measured
                      by lysimeters and meteorological data of three European
                      sites. Separate evaluations were made for the five driest
                      and five wettest April–October periods to investigate
                      whether the performance of the gap‐filling methods was
                      affected by hydrological conditions. Series of random gaps
                      were artificially created for the three time series,
                      including gaps of four different lengths. Actual ET was
                      estimated for these gaps with the gap‐filling methods,
                      which were evaluated based on RMSE and mean bias error. The
                      results show that the ratio method outperformed other
                      methods for gap filling of lysimeter data for Basel
                      (Switzerland), whereas the HYDRUS method outperformed other
                      methods for Rheindahlen (Germany). For Rietholzbach
                      (Switzerland), the different methods performed very
                      similarly, except that the FAO method gives slightly larger
                      RMSEs. The gap‐filling methods do not perform very
                      differently for dry and wet conditions. The ratio method is
                      recommended for filling smaller gaps, and the HYDRUS method
                      is recommended for longer gaps of 30 d.},
      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:000618773300020},
      doi          = {10.1002/vzj2.20020},
      url          = {https://juser.fz-juelich.de/record/875091},
}