Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes

Sprenger, M.; Volkmann, T. H. M.; Blume, T.; Weiler, M.

doi:https://doi.org/10.5194/hess-19-2617-2015

Articles | Volume 19, issue 6

https://doi.org/10.5194/hess-19-2617-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-19-2617-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 19, issue 6

Research article

|

03 Jun 2015

Research article |

| 03 Jun 2015

Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes

M. Sprenger, T. H. M. Volkmann, T. Blume, and M. Weiler

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Final revised paper (published on 03 Jun 2015)
Preprint (discussion started on 10 Oct 2014)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC C5098: 'reviewer comments', Christine Stumpp, 16 Nov 2014
- AC C5277: 'Response by the authors to the comments of C. Stumpp', Matthias Sprenger, 24 Nov 2014
RC C5671: 'hess-2014-405', Anonymous Referee #2, 14 Dec 2014
- AC C5812: 'Response by the authors to the comments of Anonymous Referee#2', Matthias Sprenger, 26 Dec 2014

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (21 Dec 2014) by Mauro Giudici

AR by Matthias Sprenger on behalf of the Authors (02 Mar 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (08 Mar 2015) by Mauro Giudici

RR by Anonymous Referee #2 (22 Mar 2015)

Suggestions for revision or reasons for rejection

Besides a few minor suggestions, I have only one remaining concern about the paper and that is the sensitivity analysis that is presented. I am not sure whether the approach that the authors use is meaningful since I think that it rather reflects the efficiency of the optimization algorithm to find the optimum. Whether the obtained distribution of parameter sets can be used to conclude something about the parameter sensitivity and the model prediction uncertainty is not clear to me.

Detailed comments:
Ln 47: Still I think ‘transforming‘ is not the right word choice here. It means to change in composition or structure. Water does not change in structure when it is transferred from the soil to the groundwater or to the vegetation. I would propose ‘redistributing’ or ‘transferring’.
Ln 47: ground water --> groundwater
Ln 79: ‘… serving as variables in objective functions for water flow and transport parameter optimization’
ln 127: replace ‘diffusivity’ by ‘dispersion length’ or ‘dispersivity’. You do not fit the dispersion coefficient but the dispersion length.
ln 145 and ln 148: Is a ‘parameter representation’ equivalent to a ‘system’s model’?
ln 248: where the ranges for optimal transpiration dependent on the transpiration rate?
Ln 312: I suppose a zero gradient in isotope concentration was used as an upper boundary when the flow was directed out of the domain (soil evaporation) and a third type boundary condition with specified isotope flux concentration when flow was directed into the domain (precipitation and throughfall).
Ln 351: Shouldn’t it be: … was constrained… instead of … was not constrained… ?
Ln 366: I am not convinced that the sensitivity analysis makes sense. By taking all parameter combinations with a KGE that is not more than 0.05 different from the best KGE and taking then the 10-90 % range of this population, the result that is obtained depends strongly on the efficiency of the search algorithm to find the optimum rather than on the sensitivity of the parameters. The SCE-UA does not preserve the posterior parameter distribution but favors the selection of more optimal parameter sets. Why not taking all parameter combinations with a given KGE deviation (or range of deviations) from the optimum? Then the sensitivity would not depend on how many parameter combinations are close to the KGE optimum, which in the SCE-UA depends on the efficiency with which the optimum can be found.

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RR by Christine Stumpp (31 Mar 2015)

ED: Publish subject to minor revisions (Editor review) (12 Apr 2015) by Mauro Giudici

AR by Matthias Sprenger on behalf of the Authors (22 Apr 2015) Author's response Manuscript

ED: Publish as is (10 May 2015) by Mauro Giudici

AR by Matthias Sprenger on behalf of the Authors (12 May 2015)

Short summary

We present a novel approach that includes information about the pore water stable isotopic composition in inverse model approaches to estimate soil hydraulic parameters. Different approaches are presented and their adequacy regarding the model efficiency, realism and parameter identifiability are discussed. The advantages of the new approach are shown by an application of the inverse estimated parameters to infer the water balance and the transit time for three different study sites.