Evaluation of root water uptake in the ISBA-A-gs land surface model using agricultural yield statistics over France

Canal, N.; Calvet, J.-C.; Decharme, B.; Carrer, D.; Lafont, S.; Pigeon, G.

doi:https://doi.org/10.5194/hess-18-4979-2014

Articles | Volume 18, issue 12

https://doi.org/10.5194/hess-18-4979-2014

© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-18-4979-2014

© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 18, issue 12

Research article

|

10 Dec 2014

Research article |

| 10 Dec 2014

Evaluation of root water uptake in the ISBA-A-gs land surface model using agricultural yield statistics over France

N. Canal, J.-C. Calvet, B. Decharme, D. Carrer, S. Lafont, and G. Pigeon

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Final revised paper (published on 10 Dec 2014)
Supplement to the final revised paper
Preprint (discussion started on 23 May 2014)

Interactive discussion

Status: closed

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

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- Supplement

RC C1974: 'Comments to authors', Anonymous Referee #1, 22 Jun 2014
- AC C2766: 'Response to Referee #1', Jean-Christophe Calvet, 28 Jul 2014
RC C2068: 'Unclear message', Anonymous Referee #2, 27 Jun 2014
- AC C2772: 'Response to Referee #2', Jean-Christophe Calvet, 28 Jul 2014
EC C2164: 'start interacting', Nunzio Romano, 01 Jul 2014
- AC C2783: 'Response to the Editor', Jean-Christophe Calvet, 28 Jul 2014
RC C3106: 'General comments', Anonymous Referee #3, 15 Aug 2014
- AC C3876: 'Response to Referee #3', Jean-Christophe Calvet, 18 Sep 2014

Peer-review completion

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

ED: Reconsider after major revisions (19 Aug 2014) by Nunzio Romano

AR by Jean-Christophe Calvet on behalf of the Authors (30 Sep 2014) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Oct 2014) by Nunzio Romano

RR by Anonymous Referee #2 (24 Oct 2014)

Suggestions for revision or reasons for rejection

The authors have made an effort to change the manuscript and take into account the reviewers comments. Some of my comments were addressed, but others were either not understood or not taken as importantly. I believe the following things still need to be addressed in the manuscript:

(1) I requested a discussion of the fact that the model in Equation 5 is known to limit transpiration too early. I believe the authors have not caught on this comment enough. In their response they comment on the fact that this issue is not so relevant for them since they work with water content not water potential. They did however look into the recommended reference and cited additional research. I agree with the citations, but there is more. I want to make my point again, and I have attached a Figure to illustrate it. I am using Eq 1 and 5, with rooting depth = 1.6m and R_e=0.97 (just for illustration-this can be repeated with any parameters to obtain the same pattern). Now I changed water availability as shown in the attached figure (in the blue case the upper soil is drier than the bottom and black the other way around). Fs(i) is plotted on the right hand side and while the Fs of black sums up to almost 1, blue only sums up to 0.55. There is some compensation, but very little. Now the main question is: How is Ft calculated (Eq. 6). In many models it is simply: Ft = To * Fs, with To the potential Transpiration. If this is the case in the ISBA model (needs to be stated, there is only qualitative information), transpiration is severely limited in the blue case although a great deal of water is still available at depth. This is the problem stated in Feddes et al (2001) and needs to be discussed. Plants are able to transfer water uptake to compensate water stress in the top layers, and this model can not adequately account for it. This fact probably explains part of why this model performs rather poorly.

I would like to emphasize also that the problem is not with the Jackson model (This power decrease or root length density is likely valid), but with the fact how it is implemented with the model to obtain water stress and stomatal closure. The discussion currently addresses the Jackson model (Eq.1), when it should address Eq. 5-6, and state that other options may have more success.

(2) I am really worried about the fact that there was apparently no separation between a calibration and validation period. If I understand correctly, the presented model quality matrices were obtained for the calibration run (The model was optimized to maximize the correlation coefficient between AGRESTE GY and modeled Bag. The same data are used to assess the model quality.). This does however not reflect the quality of the model, which can be confirmed in an independent run with data not used during the calibration, since calibration of a complex model may lead to interaction with other parameters and may not represent the real process any more. At the minimum this fact should be stated in the discussion, maybe using Refsgaard (1997) as a starting point (although it is from a different discipline) and work citing this.

(3) Minor point: Please change Eq. 2-3, use mathematical expression rather than prose and nomenclature to express what is meant. This will really improve deciphering what is done. If I understand correctly, than Eq. 2 is SWI_top = sum_{i=0}^{i=k}(…), where k is the index of the deepest layer considered as “top”. SWI(d_L,i) could become SWI_i to keep things simpler. I also think that FS(i) in Eq3 would better be FS_i .

References:

Feddes, R. A., Hoff, H., Bruen, M., Dawson, T., De Rosnay, P., Dirmeyer, O., Jackson, R. B., Kabat, P., Kleidon, A., Lilly, A. and Pitman, A. J.: Modeling root water uptake in hydrological and climate models, Bulletin Of The American Meteorological Society, 82(12), 2797–2809, 2001.

Refsgaard, J.C. Parameterisation, calibration and validation of distributed hydrological models, Journal of Hydrology, 198(1-4)69-97, 1997.

Referee Report: PDF

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RR by Anonymous Referee #3 (24 Oct 2014)

ED: Publish subject to minor revisions (Editor review) (28 Oct 2014) by Nunzio Romano

AR by Jean-Christophe Calvet on behalf of the Authors (02 Nov 2014) Author's response Manuscript

ED: Publish as is (12 Nov 2014) by Nunzio Romano

AR by Jean-Christophe Calvet on behalf of the Authors (12 Nov 2014)

Short summary

Regional French agricultural yield statistics are used to benchmark root water uptake representations in the ISBA-A-gs model. Key model parameters governing the inter-annual variability of the simulated biomass are retrieved. A complex multi-layer soil hydrology model does not outperform a simple bulk root-zone reservoir approach. This could be explained by missing processes/information in the model such as hydraulic redistribution and detailed soil properties.