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@ARTICLE{Waldowski:1007405,
      author       = {Waldowski, Bastian and Sánchez-León, Emilio and Cirpka,
                      Olaf A. and Brandhorst, Natascha and Hendricks Franssen,
                      Harrie-Jan and Neuweiler, Insa},
      title        = {{E}stimating {G}roundwater {R}echarge in {F}ully
                      {I}ntegrated pde ‐{B}ased {H}ydrological {M}odels},
      journal      = {Water resources research},
      volume       = {59},
      number       = {3},
      issn         = {0043-1397},
      address      = {[New York]},
      publisher    = {Wiley},
      reportid     = {FZJ-2023-02061},
      pages        = {e2022WR032430},
      year         = {2023},
      abstract     = {Groundwater recharge is the main forcing of regional
                      groundwater flow. In traditional
                      partial‐differential‐equation (pde)‐based models that
                      treat aquifers as separate compartments, groundwater
                      recharge needs to be defined as a boundary condition or it
                      is a coupling condition to other compartments. Integrated
                      models that treat the vadose and phreatic zones as a
                      continuum allow for a more sophisticated calculation of
                      subsurface fluxes, as feedbacks between both zones are
                      captured. However, they do not contain an explicit
                      groundwater‐recharge term so it needs to be estimated by
                      post‐processing. Groundwater recharge consists of changes
                      in groundwater storage and of the flux crossing the water
                      table, which can be calculated based on hydraulic gradients.
                      We introduce a method to evaluate the change of groundwater
                      storage by a time‐cumulative water balance over the depth
                      section of water table fluctuations, avoiding the use of a
                      specific yield. We demonstrate the approach first by a
                      simple 1‐D vertical model that does not allow for lateral
                      outflow and illustrates the ambiguity of computing
                      groundwater recharge by different methods. We then apply the
                      approach to a 3‐D model with a complex topography and
                      subsurface structure. The latter example shows that
                      groundwater recharge is highly variable in space and time
                      with notable differences between regional and local
                      estimates. Local heterogeneity of topography or subsurface
                      properties results in complex redistribution patterns of
                      groundwater. In fully integrated models, river‐groundwater
                      exchange flow may severely bias the estimate of groundwater
                      recharge. We, therefore, advise masking out groundwater
                      recharge at river locations.},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {2173 - Agro-biogeosystems: controls, feedbacks and impact
                      (POF4-217)},
      pid          = {G:(DE-HGF)POF4-2173},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000952884600001},
      doi          = {10.1029/2022WR032430},
      url          = {https://juser.fz-juelich.de/record/1007405},
}