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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/hess-2020-317
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2020-317
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  30 Jul 2020

30 Jul 2020

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A revised version of this preprint is currently under review for the journal HESS.

Intercomparison of freshwater fluxes over ocean and investigations into water budget closure

Marloes Gutenstein1, Karsten Fennig1, Marc Schröder1, Tim Trent2, Stephan Bakan3, J. Brent Roberts4, and Franklin R. Robertson4 Marloes Gutenstein et al.
  • 1Deutscher Wetterdienst, Offenbach, Germany
  • 2University of Leicester, Leicester, United Kingdom
  • 3Max Planck Institute for Meteorology, Hamburg, Germany
  • 4NASA Marshall Space Flight Center, Huntsville, AL, USA

Abstract. The development of algorithms for the retrieval of water cycle components from satellite data, such as total column water vapor content (TCWV), precipitation (P), latent heat flux, and evaporation (E) has seen much progress in the past three decades. In the present study, we compare six recent satellite-based retrieval algorithms and ERA5 (the European Centre for Medium-Range Weather Forecasts' fifth reanalysis) freshwater flux (E–P) data regarding global and regional, seasonal and inter-annual variation to assess the degree of correspondence among them. The compared data sets are recent, freely available and documented climate data records (CDRs), developed with a focus on stability and homogeneity of the time series, as opposed to instantaneous accuracy.

One main finding of our study is the agreement of global ocean means of all E–P data sets within the uncertainty ranges of satellite-based data. Regionally, however, significant differences are found among the satellite data and with ERA5. Regression analyses of regional monthly means of E, P, and E–P against the statistical median of the satellite data ensemble (SEM) show that, despite substantial differences in global E patterns, deviations among E–P data are dominated by differences in P throughout the globe. E–P differences among data sets are spatially inhomogeneous.

We observe that for ERA5 long-term global E–P is very close to 0 mm/day and that there is good agreement between land and ocean mean E–P, vertically integrated moisture divergence (VIMD), and global TCWV tendency. The fact that E and P are balanced globally provides an opportunity to investigate the consistency between E and P data sets. Over ocean, P (nearly) balances with E if the net transport of water vapor from ocean to land (over-ocean VIMD, i.e., ∇Qocean) is taken into account. Correlation of Eocean − ∇Qocean with Pocean yields R2 = 0.86 for ERA5, but smaller R2 are found for satellite data sets.

Climatological global yearly totals of water cycle components (E, P, E–P, and net transport from ocean to land and vice versa) calculated from the data sets used in this study are in agreement with previous studies, with ERA5 E and P are occupying the upper part of the range. Over ocean, both the spread among satellite-based E and the difference between two satellite-based P data sets are greater than E–P and these remain the largest sources of uncertainty within the observed global water budget.

We conclude that for a better understanding of the global water budget, the quality of E and P data sets themselves and their associated uncertainties need to be further investigated.

Marloes Gutenstein et al.

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Marloes Gutenstein et al.

Marloes Gutenstein et al.

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Short summary
The net exchange of water between surface and atmosphere is mainly determined by the freshwater flux: the difference between evaporation (E) and precipitation (P), or E–P. Although there is consensus among modelers that with a warming climate E–P will increase, evidence from satellite data is still not conclusive, mainly due to sensor calibration issues. We here investigate the degree of correspondence among six recent satellite-based climate data records and ERA5 reanalysis E–P data.
The net exchange of water between surface and atmosphere is mainly determined by the freshwater...
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