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@INPROCEEDINGS{Graf:861110,
      author       = {Graf, Alexander and Klosterhalfen, Anne and Bernhofer,
                      Christian and Brümmer, Christian and Drüe, Clemens and
                      Gottschalk, Pia and Grünwald, Thomas and Heinemann,
                      Günther and Heinesch, Bernard and Klatt, Janina and
                      Konopka, Jan and De Ligne, Anne and Longdoz, Bernard and
                      Mauder, Matthias and Ney, Patrizia and Rabbel, Inken and
                      Rebmann, Corinna and Sachs, Torsten and Schmidt, Marius and
                      Schrader, Frederik and Vincke, Caroline and Völksch, Ingo
                      and Weber, Stephan and Wille, Christian and Vereecken,
                      Harry},
      title        = {{E}nergy partitioning and water use efficiency anomalies
                      2018 at {E}ddy-{C}ovariance sites across ecosystems},
      journal      = {Geophysical research abstracts},
      volume       = {21},
      issn         = {1029-7006},
      reportid     = {FZJ-2019-01675},
      pages        = {EGU2019-5834-4},
      year         = {2019},
      abstract     = {Droughts and heat waves deeply interact with the exchange
                      of energy and matter between land surface and atmosphere.
                      The conditions associated with a combined heat wave and
                      drought can have positive or negative effects on the
                      sensible heat flux (H), latent heat flux (LE), and net flux
                      of CO2 (NEE). In return, while each of these fluxes can
                      exert different local feedbacks on temperature, atmospheric
                      humidity and soil moisture, all of them result in bulk
                      heating of the troposphere (H and LE through direct local
                      and indirect non-local heat transfer, and NEE through
                      radiative forcing). H is positively affected by increased
                      solar irradiation, but can be supressed by advection of warm
                      air diminishing the gradient between surface and air
                      temperature. Potential LE is positively affected by
                      irradiation, temperature and water vapour pressure deficit,
                      but actual LE can be suppressed by stomatal closure of
                      plants and by reduced soil moisture from low rainfall and
                      high past LE. NEE is the result of plant photosynthesis
                      (GPP) and plant and soil respiration (R), both of which can
                      be enhanced by high temperatures or irradiation, and
                      suppressed by drought. Focusing on direct measurements
                      mostly by a network of Eddy-Covariance (EC) stations of the
                      ICOS (www.icosri.eu), TERENO (www.tereno.net) and other
                      networks, we hypothesize that the net effect of the 2018
                      event at a site, and thus its feedback on global warming,
                      depends on the balance between co-existing positive and
                      negative effects of the combined heat wave and drought on
                      the respective fluxes. Variables such as albedo, growing
                      degreedays (GDD), soil moisture and ecosystem-level water
                      use efficiency help to separate these co-existing positive
                      and negative effects from each other. Preliminary results
                      indicate different degrees of heterogeneity between sites
                      fordifferent variables. As expected, reduced precipitation
                      and soil moisture, as well as increased GDD, could be found
                      at almost all sites in the affected region. NEE was mostly
                      less negative, indicating a weaker sink or even a source
                      forCO2, as expected from past studies on earlier events. The
                      network density and number of site-years available now
                      confirms that this was true for all major ecosystem types -
                      forest, grassland and (rainfed) cropland, and resultedin
                      increased atmospheric CO2 concentrations. However, notable
                      exceptions occurred at elevated low mountain range sites and
                      during early stages of the event, supporting the hypothesis
                      of a balance between positive andnegative effects, where the
                      former may prevail at strongly energy-limited sites with a
                      usually large water surplus. H was mostly above-average,
                      indicating that local heat production contributed to the
                      event and was typically notsuppressed by warm air advection.
                      LE as well as inferred GPP and R reacted most
                      heterogeneously across sites, demonstrating the large
                      discrepancy between potentially high fluxes due to high
                      irradiation and temperature on theone hand, and suppression
                      by water shortage on the other hand. Despite the variability
                      in LE, its relation to NEE was such that ecosystem-level
                      water use was less efficient than usual at the majority of
                      sites through reduced CO2uptake.},
      month         = {Apr},
      date          = {2019-04-07},
      organization  = {EGU General Assembly, Vienna
                       (Austria), 7 Apr 2019 - 12 Apr 2019},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {255 - Terrestrial Systems: From Observation to Prediction
                      (POF3-255) / IDAS-GHG - Instrumental and Data-driven
                      Approaches to Source-Partitioning of Greenhouse Gas Fluxes:
                      Comparison, Combination, Advancement (BMBF-01LN1313A) /
                      TERENO - Terrestrial Environmental Observatories
                      (TERENO-2008) / DFG project 15232683 - TRR 32: Muster und
                      Strukturen in Boden-Pflanzen-Atmosphären-Systemen:
                      Erfassung, Modellierung und Datenassimilation (15232683)},
      pid          = {G:(DE-HGF)POF3-255 / G:(DE-Juel1)BMBF-01LN1313A /
                      G:(DE-HGF)TERENO-2008 / G:(GEPRIS)15232683},
      typ          = {PUB:(DE-HGF)16 / PUB:(DE-HGF)8},
      url          = {https://juser.fz-juelich.de/record/861110},
}