Influence of solar forcing, climate variability and modes of low-frequency atmospheric variability on summer floods in Switzerland

Peña, J. C.; Schulte, L.; Badoux, A.; Barriendos, M.; Barrera-Escoda, A.

doi:https://doi.org/10.5194/hess-19-3807-2015

Volume 19, issue 9

Hydrol. Earth Syst. Sci., 19, 3807–3827, 2015
https://doi.org/10.5194/hess-19-3807-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Floods and their changes in historical times – a European...

Hydrol. Earth Syst. Sci., 19, 3807–3827, 2015
https://doi.org/10.5194/hess-19-3807-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Volume 19, issue 9

Research article 10 Sep 2015

Research article | 10 Sep 2015

Influence of solar forcing, climate variability and modes of low-frequency atmospheric variability on summer floods in Switzerland

J. C. Peña et al.

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Final revised paper (published on 10 Sep 2015)
Preprint (discussion started on 19 Dec 2014)

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Status: closed

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

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RC C6177: 'Interactive comment on "Influence of solar forcing, climate variability and atmospheric circulation patterns on summer floods in Switzerland" by J.C. Pena et al.', Anonymous Referee #1, 26 Jan 2015
- AC C6596: 'Response to Reviewer 1 and 2, modified figures 4, 5 and 9.', Lothar Schulte, 06 Mar 2015
RC C6427: 'Referee comments to the manuscript "Influence of solar forcing, climate variability and atmospheric circulation patterns on summer floods in Switzerland"', Anonymous Referee #2, 10 Feb 2015
- AC C6600: 'Response to reviewers 1 and 2, modified figures 4, 5 and 9', Lothar Schulte, 06 Mar 2015
AC C6840: 'Final replies to referee comments', Lothar Schulte, 28 Apr 2015
EC C6867: 'referees' comments', Andrea Kiss, 19 May 2015

Peer review completion

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

ED: Reconsider after major revisions (22 Mar 2015) by Andrea Kiss

1) In your paper you already referred to a number of studies related to the study area and the applied methodologies. As suggested by both reviewers, please, modify this rich overview into a targeted overview concerning the place of your present investigation in the already-existing scientific literature with take more emphasis on describing what is new and innovative in your present analysis compared to these previous investigations. Also consider the application of the important additional papers suggested by Referee No. 1, and compare your analysis and results to the afore-mentioned publications.
2) As mentioned by Referee No 1, the diversion of the research area in 5 administrative regions to some extent obstructs the interpretation; a more hydrology-based division and/or, as suggested by the reviewer, a division that distinguishes between the northern and southern slopes of the Alps would be better to apply in the analysis.
3) As mentioned by both reviewers, while investigating the correlation between floods occurrence and solar activity, please also take more into consideration the volcanic activity as an influencing factor. 6) Please, according to the advice of Referee No 2, remove the applied term "summer NAO" as the NAO is primarily a winter phenomenon, and consider the suggestion of Referee No 1 whether it would be better to apply and compare flood frequencies with the MAO values.
4) It would be useful to mention in your text whether your analysis was carried out assuming stationary or non-stationary conditions.
5) As suggested by Referee No. 2, please apply the term "teleconnection patterns" instead of the applied term of "atmospheric circulation patterns" for the discussed geospatial patterns.
6) Following the suggestion of Referee No. 2, consider the fact that Vb is the local appearance of a larger scale synoptic situation primarily coming from the Atlantic.

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AR by Lothar Schulte on behalf of the Authors (05 May 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (21 May 2015) by Andrea Kiss

RR by Anonymous Referee #2 (05 Jun 2015)

Suggestions for revision or reasons for rejection

Greetings to the authors,

The reviewer begins by thanking them for the additional effort in trying to improve the manuscript.

However, by analysing the revised version, it has emerged that the authors maintain the three fatal errors raised in the previous review:

1) Failure to explicitly mention the caveats of the reconstruction of atmospheric fields up to several centuries back in time from a simple statistical extrapolation from XX century data.

2) Attributing the most dominant principal component of the atmospheric pressure fields over summer to the North Atlantic Oscillation, which is plain wrong.

As noted in the first review:
"
What is then the problem with the "Summer NAO"?

In a nutshell: the first principal component of the geopotential height field at 500 hPa (Z500) only represents the NAO in Winter. In fact, that is the only season in which the NAO is the dominant circulation pattern. Over summer the NAO is definitely not dominant. Instead, other processes take over and it is their imprint, not of NAO, that is seen in the first principal component of the summer climatologies of Z500.

In detail: There is a fundamental problem in the identification of the large scale atmospheric driver North Atlantic Oscillation (NAO). The authors mention a positive anomaly (high-pressure) centre over the North Sea (between Scandinavia and the British Isles), and a negative anomaly (low-pressure) centre over the Mediterranean.
Actually, the centres of action of the NAO lie over the Atlantic, not over the North Sea or the Mediterranean sea. The high-pressure centre is the "Azorean High", over the North Atlantic area around the Azores archipelago, and the low-pressure centre is the "Icelandic Low", over the North Atlantic area around Iceland.
The high-pressure centre close to Scandinavia is known as the Scandinavian High and represented by the Scandinavian Oscillation (SCO) Index (you can read about it in the atmospheric physics literature of at the NOAA websites).

As noted before, when performing Principal Component Analysis for the extraction of EOF of the sea level pressure fields, the NAO pressure anomaly pattern will only be dominant during Winter (e.g. December to February). During Summer other patterns take over, e.g. the SCO. This is why the first EOF over summer is no longer NAO-related, rather having completely different centres of action. Calling that "Summer NAO" is thus plain wrong.

This being said, the solution to this problem is within the authors' reach: all what the authors need to do is to remove the ill-named Summer NAO or SNAO and reinterpret the summer patterns in the light of mechanisms that actually play a dominant role at that time.
"

Just because some ill-founded literature commits the "Summer NAO" mistake, there is no excuse to perpetuate such a senseless error after the problem has been raised in the first review. A benefit of doubt had been given to the authors in the first version, but by now the error should have been corrected. Without this correction, the paper is fatally flawed.

3) On calling EOF of the geopotential height field "atmospheric circulation patterns".

Circulation patterns are wind patterns, not pressure or geopotential anomalies.

The EOF of the geopotential height field are statistical variability patterns in atmospheric geopotential height fields relative to the climatological average taken into consideration for the PCA analysis, as noted in the first review. These patterns do indeed inform indirectly on circulation (wind) patterns but are not circulation patterns per se.
By insisting on presenting pressure anomaly patterns as circulation patterns, the authors are leading the readers into a misunderstanding.

These matters are well-known textbook knowledge in undergraduate atmospheric sciences.
Still, the reviewer acknowledges that these matters may not be obvious to researchers from other fields. This is why the review of the first version had been very constructive and pedagogic.

Addressing atmospheric science matters is more than welcome and enthusiastically encouraged. However, these matters must not be taken lightly. Either they must be properly worked on, or simply removed from the manuscript.

By seeing that the authors insist on the listed mistakes despite the kind recommendations for correction, the reviewer sees no other option than to reiterate the same matters and urge the authors to be open: this is the only way that lessons can be learnt and the good promise raised by this study actually come to fruition.

Aside from the previous notes, an additional major issue has arisen from the second version of the manuscript:

4) PCA of the flood matrix:
The rotation and inversion of factors leads, allegedly, to a visual diagnostic suggestive of the geographic location of the Swiss cantons.
4.1) It should be clarified under which grounds the transformation is made to the principal components, so that it will not be perceived as purely arbitrary by the readership.
4.2) The PCA is only optimal in normally distributed data. There is no statement on the flood datasets being normally distributed (by the way, they are clearly not). Therefore, the plain use of PCA the way it is done in the paper is questionable at best. Care must be exerted when applying such geostatistical techniques, for the patterns they yield have no physical meaning otherwise.
4.3) No dynamics can be inferred from Principal Component Analysis. Only statistics (e.g. statistical variability). The authors' mention of dynamics being inferred is thus completely flawed and misleading.

All things considered, the authors are strongly encouraged to revise the manuscript and address all of the raised matters. The manuscript may only be considered for publication if, and only if, the authors proceed with all the necessary corrections.

Good luck!

Referee Report: PDF

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ED: Publish as is (20 Aug 2015) by Andrea Kiss

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Influence of solar forcing, climate variability and modes of low-frequency atmospheric variability on summer floods in Switzerland

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