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Proceedings of the International Association of Hydrological Sciences An open-access publication for refereed proceedings in hydrology
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Volume 374
Proc. IAHS, 374, 53–62, 2016
https://doi.org/10.5194/piahs-374-53-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Proc. IAHS, 374, 53–62, 2016
https://doi.org/10.5194/piahs-374-53-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

  17 Oct 2016

17 Oct 2016

Impact of climate forcing uncertainty and human water use on global and continental water balance components

Hannes Müller Schmied1,2, Linda Adam1, Stephanie Eisner3, Gabriel Fink3, Martina Flörke3, Hyungjun Kim4, Taikan Oki4, Felix Theodor Portmann1, Robert Reinecke1, Claudia Riedel1, Qi Song1, Jing Zhang1, and Petra Döll1 Hannes Müller Schmied et al.
  • 1Institute of Physical Geography, Goethe University Frankfurt, Frankfurt, Germany
  • 2Senckenberg Biodiversity and Climate Research Centre (BiK-F), Frankfurt, Germany
  • 3Center for Environmental Systems Research (CESR), University of Kassel, Kassel, Germany
  • 4Institute of Industrial Science, The University of Tokyo, Tokyo, Japan

Abstract. The assessment of water balance components using global hydrological models is subject to climate forcing uncertainty as well as to an increasing intensity of human water use within the 20th century. The uncertainty of five state-of-the-art climate forcings and the resulting range of cell runoff that is simulated by the global hydrological model WaterGAP is presented. On the global land surface, about 62 % of precipitation evapotranspires, whereas 38 % discharges into oceans and inland sinks. During 1971–2000, evapotranspiration due to human water use amounted to almost 1 % of precipitation, while this anthropogenic water flow increased by a factor of approximately 5 between 1901 and 2010. Deviation of estimated global discharge from the ensemble mean due to climate forcing uncertainty is approximately 4 %. Precipitation uncertainty is the most important reason for the uncertainty of discharge and evapotranspiration, followed by shortwave downward radiation. At continental levels, deviations of water balance components due to uncertain climate forcing are higher, with the highest discharge deviations occurring for river discharge in Africa (−6 to 11 % from the ensemble mean). Uncertain climate forcings also affect the estimation of irrigation water use and thus the estimated human impact of river discharge. The uncertainty range of global irrigation water consumption amounts to approximately 50 % of the global sum of water consumption in the other water use sector.

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We analyzed simulated water balance components on global and continental scale as impacted by the uncertainty of climate forcing datasets. On average, around 62 % of precipitation on global land area evapotranspires and 38 % is discharge to oceans and inland sinks. Human water use increased during the 20th century by a factor of 5. Uncertainty of precipitation variable has most impact on model results, followed by shortwave downward radiation. Model calibration reduces this uncertainty.
We analyzed simulated water balance components on global and continental scale as impacted by...
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