The uncertainty of flood frequency analyses in  hydrodynamic model simulations

Zhou, Xudong; Ma, Wenchao; Echizenya, Wataru; Yamazaki, Dai

doi:https://doi.org/10.5194/nhess-21-1071-2021

Articles | Volume 21, issue 3

https://doi.org/10.5194/nhess-21-1071-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/nhess-21-1071-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 3

Research article

|

23 Mar 2021

Research article |

| 23 Mar 2021

The uncertainty of flood frequency analyses in hydrodynamic model simulations

Xudong Zhou, Wenchao Ma, Wataru Echizenya, and Dai Yamazaki

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Final revised paper (published on 23 Mar 2021)
Supplement to the final revised paper
Preprint (discussion started on 26 Aug 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of Zhou et al., "Uncertainty in flood frequency analysis of hydrodynamic model simulations"', Anonymous Referee #1, 03 Sep 2020
- AC1: 'Replies to Referee #1', Xudong Zhou, 17 Nov 2020
RC2: 'Review of "Uncertainty in flood frequency analysis of hydrodynamic model simulations"', Anonymous Referee #2, 14 Sep 2020
- AC2: 'Replies to Referee #2', Xudong Zhou, 17 Nov 2020

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (25 Nov 2020) by Heidi Kreibich

AR by Xudong Zhou on behalf of the Authors (19 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (19 Jan 2021) by Heidi Kreibich

RR by Anonymous Referee #2 (21 Jan 2021)

RR by Anonymous Referee #1 (26 Jan 2021)

Suggestions for revision or reasons for rejection

The authors are to be commended for the improvements to their manuscript and the interesting results they present. A number of issues still remain outstanding, however, which require addressing before publication is to be considered:

1. Language remains an issue in this manuscript. I appreciate the efforts of the authors, but the language as a whole remains difficult to follow and poor translation has led to some questionable commentary in some places. The copyeditors of the journal will be able to help with some of the more cosmetic errors, but the substantive meaning of what has been said needs to be checked by the authors. In particular, I'm not sure diagnostic/prognostic variables is a useful descriptor, and in the abstract it states that runoff is 80% of total uncertainties -- please make clear this is the total of considered uncertainties, given an analysis of very large uncertainties (e.g. terrain data errors, river bathymetry) is not considered.

2. I still do not think the section on the AIC analysis provides useful conclusions in understanding model skill. The floods being simulated are extrapolations from these distributions, and the degree to which they fit 35 years of data does not illustrate how useful they are for extrapolation. If I am wrong about this, then please add further discussion explaining why this is a relevant test of the model, as I am presently unconvinced.

3. Some interpretations of the results and comparison with the literature do appear quite tokenistic, rather than contributing to a rich discussion. E.g. P18 L3-13 loosely says routing is and is not important. P18 L14-24 is a little rushed in its review of these papers and it is not clear how this relates to the study in question. P11 L5-10 suggests the spatial patterns are not consistent with Schellekens et al., but I disagree. Although the proportion of the contribution to the uncertainty by runoff forcing is fairly consistent in space (Fig 4e), the magnitude of the uncertainty (Fig 4c; the relevant figure for the point being made about Schellekens' conclusion) is larger in mountainous and arid regions.

4. Section 3.3 is still a fairly long-winded way of saying that runoff is most important. I would suggest condensing 3.3.1 and 3.3.2 without using so much text, as the conclusion is quite simple -- consider what the reader truly needs to know. A GRDC gauge is mentioned, but then no analysis is done using this, which is confusing. Section 3.3.3 is interesting, but the authors should be much more explicit about the uncertainties in the exposure data they are using: how accurate is 1km resolution population data? If you analysed sensitivities with the 90m flood model with higher resolution population data, I expect conclusions would be very different. There is lots of literature on the accuracy of these global population datasets and the impact of resolution that should be discussed.

5. Some figures require improvement. The x axes on Figs 6+7 make no sense. Fig 5 is too small also (where is the yellow cross?).

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ED: Publish subject to minor revisions (review by editor) (27 Jan 2021) by Heidi Kreibich

AR by Xudong Zhou on behalf of the Authors (08 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (13 Feb 2021) by Heidi Kreibich

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Short summary

This article assesses different uncertainties in the analysis of flood risk and found the runoff generated before the river routing is the primary uncertainty source. This calls for attention to be focused on selecting an appropriate runoff for the flood analysis. The uncertainties are reflected in the flood water depth, inundation area and the exposure of the population and economy to the floods.