The paradoxical evolution of runoff in the pastoral Sahel: analysis of the hydrological changes over the Agoufou watershed (Mali) using the KINEROS-2 model

Gal, Laetitia; Grippa, Manuela; Hiernaux, Pierre; Pons, Léa; Kergoat, Laurent

doi:https://doi.org/10.5194/hess-21-4591-2017

Articles | Volume 21, issue 9

https://doi.org/10.5194/hess-21-4591-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-21-4591-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 21, issue 9

Research article

|

13 Sep 2017

Research article |

| 13 Sep 2017

The paradoxical evolution of runoff in the pastoral Sahel: analysis of the hydrological changes over the Agoufou watershed (Mali) using the KINEROS-2 model

Laetitia Gal, Manuela Grippa, Pierre Hiernaux, Léa Pons, and Laurent Kergoat

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Final revised paper (published on 13 Sep 2017)
Preprint (discussion started on 25 Nov 2016)

Interactive discussion

Status: closed

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

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RC1: 'Referee comments', Jean-Emmanuel PATUREL, 19 Dec 2016
- AC1: 'Response to hess-2016-623 RC#1', Laetitia Gal, 17 Feb 2017
RC2: 'Review: Gal et al.', Anonymous Referee #2, 20 Dec 2016
- AC2: 'Response to hess-2016-623 RC#2', Laetitia Gal, 17 Feb 2017
RC3: 'Interactive comment on “Modelling the paradoxical evolution of runoff in pastoral Sahel. The case of the Agoufou watershed, Mali”, by L. Gal et al.', Anonymous Referee #3, 20 Dec 2016
- AC3: 'Response to hess-2016-623 RC#3', Laetitia Gal, 17 Feb 2017
RC4: 'Comments on “Modeling the paradoxical evolution of runoff in pastoral Sahel. The case of the Agoufou watershed, Mali”', Anonymous Referee #4, 27 Dec 2016
- AC4: 'Response to hess-2016-623 RC#4', Laetitia Gal, 17 Feb 2017
RC5: 'Referee Comment', Anonymous Referee #5, 03 Jan 2017
- AC5: 'Response to hess-2016-623 RC#5', Laetitia Gal, 17 Feb 2017
EC1: 'Editor Comment', Murugesu Sivapalan, 03 Jan 2017
- AC6: 'Response to hess-2016-623 Editor', Laetitia Gal, 17 Feb 2017

Peer-review completion

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

ED: Reconsider after major revisions (further review by Editor and Referees) (06 Mar 2017) by Murugesu Sivapalan

AR by Anna Mirena Feist-Polner on behalf of the Authors (18 Apr 2017) Author's response Manuscript

ED: Reconsider after major revisions (further review by Editor and Referees) (02 May 2017) by Murugesu Sivapalan

ED: Referee Nomination & Report Request started (05 May 2017) by Murugesu Sivapalan

RR by Anonymous Referee #2 (29 May 2017)

Suggestions for revision or reasons for rejection

The manuscript was improved and it is more clear now. I am also quite satisfied with the author ‎response to my comments. There is however one point which I do not think was addressed ‎adequately and this is the assumption of rain cells covering the entire catchment. I have some ‎doubts about this. The authors provide comparison of rainfall distribution between different ‎location, but this is not relevant. Two locations can have a similar climatology in terms of rain ‎intensity distribution, but still at a given moment different rain intensity are measured. To support ‎the assumption that rain cells cover the entire catchment the authors should present the scatter of ‎observed rain intensity at the same time from two gauges (for example the one near the outlet ‎and the one within the catchment). ‎
The authors also refer to Gal’s thesis, but I could not read it since it is in French. Looking at the MSG ‎images presented in the thesis it is hard to tell what is the “cell” size since cloud top temperatures ‎are shown and how they are translated to rain rates is not clear from the images. There are rainfall ‎products at high resolution (~4 km, 30-min) that could be used to demonstrate this point in a ‎better way. Also, the authors refer t a possible variability of rainfall but the write in page 8 line 18: ‎‎“This variability is significantly smoothed out at the annual time step but still persists and ‎constitutes an uncertainty”. But runoff response is not at the annual scale but on the event scale, ‎and surely it is sensitive to rainfall variability. ‎
In my opinion, it is better not to claim for a uniform coverage if the authors are not sure about it. ‎Other studies have shown rain cells are often in the size of few tens of square km, so even if we ‎take the relevant third of the catchment, the location of the rain cell totally change the rain ‎intensity over this area. ‎
I think the way to go is to introduce somehow (in a random way or assuming a certain structure) ‎the intra-catchment rainfall variability into the simulations and show their conclusions are not very ‎sensitive to this variability. I assume the computed runoff for each event will be quite different if ‎some variability will be introduced comparing to the uniform rain assumption, but the final mean ‎volume for the two periods will still have a large difference and the main causes of this difference ‎will not change.‎
Minor comments: add “potential” before evaporation in page 3 line 37‎

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RR by Jean-Emmanuel Paturel (29 May 2017)

RR by Anonymous Referee #3 (11 Jun 2017)

ED: Publish subject to revisions (further review by Editor and Referees) (19 Jun 2017) by Murugesu Sivapalan

AR by Anna Mirena Feist-Polner on behalf of the Authors (01 Aug 2017) Author's response

ED: Publish subject to minor revisions (further review by Editor) (01 Aug 2017) by Murugesu Sivapalan

AR by Laetitia Gal on behalf of the Authors (01 Aug 2017) Author's response Manuscript

ED: Publish as is (04 Aug 2017) by Murugesu Sivapalan

Short summary

The intense, prolonged Sahel drought has caused a widespread increase in surface runoff and surface waters like lakes or rivers, against all expectations. Using long-term observations and the Kineros2 hydrological model, we show that the runoff coefficient of the Agoufou watershed increased from ~ 0 to 5.5 % in 1950–2011. We attribute this phenomenon to a change in vegetation and soil surface properties, in response to the drought, rather than land–use change or rainfall regime intensification.