Impact of climate change on hydrological conditions in a tropical West African catchment using an ensemble of climate simulations

Yira, Yacouba; Diekkrüger, Bernd; Steup, Gero; Bossa, Aymar Yaovi

doi:https://doi.org/10.5194/hess-21-2143-2017

Articles | Volume 21, issue 4

https://doi.org/10.5194/hess-21-2143-2017

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

https://doi.org/10.5194/hess-21-2143-2017

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

Articles | Volume 21, issue 4

Research article

|

20 Apr 2017

Research article |

| 20 Apr 2017

Impact of climate change on hydrological conditions in a tropical West African catchment using an ensemble of climate simulations

Yacouba Yira, Bernd Diekkrüger, Gero Steup, and Aymar Yaovi Bossa

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Final revised paper (published on 20 Apr 2017)
Supplement to the final revised paper
Preprint (discussion started on 07 Sep 2016)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Comments', Anonymous Referee #1, 26 Sep 2016
- AC1: 'Answers to referee #1', Yacouba YIRA, 03 Nov 2016
RC2: 'Reviewer 2 Comments', Anonymous Referee #2, 05 Dec 2016
- AC2: 'Answers to Referee #2', Yacouba YIRA, 27 Dec 2016

Peer-review completion

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

ED: Reconsider after major revisions (further review by Editor and Referees) (10 Jan 2017) by Erwin Zehe

Dear Dr. Yira,

I had a close look at your manuscript, the reviewer comments and your very much appropriate responses. In line with the reviewers I see that the study may potentially become an interesting contribution to HESS. However, in the present form the manuscript is with respect to the presentation quality and the degree of scientific innovation not up to the standards required for a publication as a research paper, it has much more of a cutting edge case study (which is another manuscript type that may be published in HESS). Both reviewers point out that the main innovative aspect of your study is the small size of the target catchment and raised major points that should be addressed in the revised manuscript. Particularly the issue of scale in-compatibility of the data you used for bias correction raised by reviewer II needs to be taken seriously. Additionally, I found your manuscript not self-contained; neither the bias correction nor the setup of WASIM ETH is sufficiently explained. Last not least I miss a) a critical evaluation of the bias correction of precipitation within a split sampling and a b) critical evaluation of the goodness of fit criteria you used to evaluate WASIM given the strong seasonality in rainfall runoff in this area.

A) Bias correction is in fact a calibration of the modelled precipitation to observations. Any calibration needs to be evaluated in a split sampling! This can be easily achieved by using the first 10 years of your observation period for calibration and the second 10 year for verification of the bias corrected precipitation. This way you may obtain the transferability of the scheme to another decade. This is crucial test to justify the stationarity assumption of the bias correction scheme under changing conditions.

B) It is well known that the Nash is not an appropriate GOF criterion in case of strongly seasonal rainfall runoff regimes, because the annual cycle in precipitation input introduces already quite some skill into a discharge simulation. The real null model is not the average discharge but the average annual cycle of daily discharge.

Additionally those points the revised manuscript should address the following technical points.
- WASIM is not a proper keyword, it is a model name
- Please use a precise language e.g. in line 75 you speak “of water flow in catchments,” which flows do you mean?
- Explain which version of WASIM was used TOP-Model version or the Richards version, provide details on the estimated parameters
- Please stick to the manuscript guidelines with respect to presentation of variables and equations

Best wishes,

Erwin Zehe

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AR by Yacouba Yira on behalf of the Authors (15 Feb 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (16 Feb 2017) by Erwin Zehe

RR by Anonymous Referee #1 (23 Feb 2017)

RR by Anonymous Referee #2 (20 Mar 2017)

Suggestions for revision or reasons for rejection

Reviewer 2
Yira et al.: Impact of climate change on water resources in a tropical West African catchment using an ensemble of climate simulations

The authors included the my comments in an appropriate manner and significantly improved the manuscript. Nevertheless, I request to revise the following (minor) points.

1.) Referring to point 2 of the Reviewer 2 comments concerning the different scales of climate models (50x50 km2) and the Danu catchment size (200km2):
Autors reply:“Only considering climate variables of the nearest RCM grid point to the Dano catchment would be meaningless since the nominal resolution of RCMs does not correspond to the effective resolution (..).”
This was exactly the point I was refering to with this comment.

Authors reply: “Therefore, we had to consider a larger RCM domain to represent the simulated climate within the Dano catchment (20 nodes domain was applied). (...) To overcome these issues we adoped the “one node at a time approach” and the 20 nodes were used”. and article p. 8, L. 130ff: “ Due to the discrepancy between the RCM-GCM data resolution and the hydrological modelling domain the data of eache node were seperatly used as climate input for the hydrological simulation model. Therefore, for each period (..) 20 simulations corresponding to the 20 nodes are performed per RCM-GCM (... and) then calculated as arithmetic mean.”
I totally agree with your reply. Actually, I see this “one node at a time approach” as the main methodical innovation of this study. This appoach enables the use of climate model input for very small scale catchments which are smaller than the size of one climate model grid cell and, hence, an approximately climate impact analyses for very small scale catchments. I recommend to highlight this more clearly in the study.

Refering to that:
P 19, L 467: “The approach appears suitable to display the ,results of climate change impact on catchment hydrology.” -> I recommend to highlight: ...on catchment hydrology of small scale catchments!

2.) The study focuses mainly on the analysis of climate model simulations with a hydrological focus and uses an hydrological model to simulate river discharge on a small scale. I think, the titel does not capture the content of the study as it refers to “water resources”, which include other hydrological aspects than precipitation, evapo(transpi)ration and river discharge. Here I rater suggest to use the term “hydrological conditions” (or similar).

3.) This comment is also roughly related to point 2.
p19, L. 465ff: “The ecological concept (..) in this study proved to fully capture climate change impact on the catchment hydrology as both discharge change signal, precipitation and (..) evapotranspiration change signal are consistently displayed by the E-P plot. (...) it further brings insights about the catchment environmental conditions (..).”
To my view, the study only focuses on hydro-climatical conditions and river discharge at the outlet station. It does not “fully capture climate change impacts on the catchment hydrology”, which includes also other aspects like interception, infiltation, subsurface runoff and groundwater flow. Also the new “insights about catchment environmental conditions”, instead of hydro-climatic conditions, are not clearly discernible to me.

4.) I suggest to include in the manuscript the author’s reply on the short calibration period and that it was shown by Yira et al. 2016 that both calibration and validation period reflect the rainfall pattern for a longer period.

5.) I further suggest to revise the section P. 18, L. 432ff:

P. 18, L. 432: “All the climate models that projects a precipitation increase result in an ETa increase.”
This is not surprisingly as all climate model simulations project/include an increase in temperature.

ff: “This indicates that the catchment ecosystem (as defined as the vegetation within the catchment and provided by the land use and land cover map of the catchment) is able to optimize the use of water and energy available in the environment, thus reducing unused water with temperature increase.
I do not understand this sentence, especially not the term “unused water” in this context.

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ED: Publish subject to minor revisions (further review by Editor) (22 Mar 2017) by Erwin Zehe

AR by Yacouba Yira on behalf of the Authors (25 Mar 2017) Author's response Manuscript

ED: Publish as is (28 Mar 2017) by Erwin Zehe

AR by Yacouba Yira on behalf of the Authors (28 Mar 2017)

Short summary

The current study aims to investigate the future climate change impacts on the hydrology of the Dano catchment in Burkina Faso, thus contributing to the management of water resources in the region. Temperature and bias corrected precipitation data from an ensemble of six RCMs–GCMs were used as input for the Water flow and balance Simulation Model to simulate water balance components. The results indicate potential increase and decrease in future discharge in the catchment.