Change detection of bare-ice albedo in the Swiss Alps

Naegeli, Kathrin; Huss, Matthias; Hoelzle, Martin

doi:https://doi.org/10.5194/tc-13-397-2019

Articles | Volume 13, issue 1

https://doi.org/10.5194/tc-13-397-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/tc-13-397-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 13, issue 1

Research article

|

01 Feb 2019

Research article |

| 01 Feb 2019

Change detection of bare-ice albedo in the Swiss Alps

Kathrin Naegeli, Matthias Huss, and Martin Hoelzle

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Final revised paper (published on 01 Feb 2019)
Supplement to the final revised paper
Preprint (discussion started on 29 Jan 2018)

Interactive discussion

Status: closed

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

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- Supplement

SC1: 'citation', Thomas Goelles, 13 Feb 2018
- AC3: 'Response to short comment', Kathrin Naegeli, 17 Apr 2018
RC1: 'Review of Naegeli et al.', Anonymous Referee #1, 26 Feb 2018
- AC1: 'Response to anonymous referee #1', Kathrin Naegeli, 17 Apr 2018
RC2: 'Review of Naegeli et al.', Anonymous Referee #2, 01 Mar 2018
- AC2: 'Response to anonymous referee #2', Kathrin Naegeli, 17 Apr 2018

Peer-review completion

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

AR by Kathrin Naegeli on behalf of the Authors (29 Aug 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (14 Sep 2018) by Marie Dumont

RR by Anonymous Referee #2 (28 Sep 2018)

Suggestions for revision or reasons for rejection

Dear Editor,

I thank the authors for considering my comments and submitting a revised version of their manuscript. Importantly, the authors considered my main concern about their conclusion by refining their glacier mask to exclude from the analysis some obvious areas of glaciers that did not qualify as bare-ice, namely medial moraines and areas where tributaries separated from the main glacier. I also appreciate that the authors tidied up the numerous oversights in dates of the images being used. It will certainly facilitate the consideration of this work in the future.

Despite this modification, I however regret I do not find in this revision a large enough improvement to address fully my overarching concerns. Despite this adjustment in the methodology and revised results, I still find that the areas of significant change in albedo remain largely indicative of step-change in surface conditions, change in flow and possibly compounded with imperfect co-registration that I find confusingly presented as a regional subtle decrease in bare-ice albedo. I don’t think that the pattern of significant trends presented in Figure 5 and 6 when scrutinized with the corresponding images in the context of glacier flow and demise, fully and unambiguously support the conclusions being drawn or the way there are presented. Figure 7 although restrictive in space remains revealing of the obvious departure between what appears discussed as a general trend and what pattern of change the analysis truly reveals. To some extent, I find the authors attach a lot of importance to the overall negative trend without fully discarding that the trend may be an effect of the relative share of bare-ice becoming largely debris-covered in a context of glacier recession, and despite some amendments to the glacier mask. Although this phenomenon is mentioned, I don’t think its full effect on the general conclusion is fairly represented. To some extent, the pattern of significant changes should equally invite to discuss areas of positive trend, which are however ignored. Since no trend is detected overall, the question of where and how much the albedo has risen to compensate the decrease in ablation areas could also be expected. This revision therefore does not fundamentally change my perception of a disconnect between the overall conclusions and what I believe can be interpreted from the results. The fact that the title remains a provocative question is also, to me, revealing of an analysis that is finally not truly conclusive as I suggested in my earlier comments.

The fact that the study to assess change at the scale of each glacier considers variable bare-ice area that depend on the size of the remaining accumulation area for each year remains problematic. The albedo of ice is not equal everywhere and one could argue that albedo of bare ice would tend to decrease towards the terminus. In this study, the weight of such effect is unequal through each year and to me remain a methodological issue that the author did not address in a way that I find suitable.

Another example of obvious issues I can see is found in the map of albedo of Findelengletscher for 2016 in Figure 3. The potential effects of cloud misclassification remains visible close to the terminus. In this regard, I find that my earlier comment about the cloud masking approach is not convincingly addressed.

I also stand by my earlier comment that the claim of albedo products being of “very high accuracy” and the reference of average deviation being less than 0.001 misrepresentative or ambiguous despite the author’s response. I note that the authors stressed and introduced sources of uncertainties far more that in the earlier version. While addressing some of my specific comments, I don’t find that this brought much of the expected modulation to their conclusion.

In view of all the above, I therefore recommend that this manuscript be rejected for publication in The Cryosphere.

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RR by Anonymous Referee #1 (02 Oct 2018)

ED: Reconsider after major revisions (08 Oct 2018) by Marie Dumont

AR by Kathrin Naegeli on behalf of the Authors (14 Nov 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (20 Nov 2018) by Marie Dumont

RR by Anonymous Referee #1 (28 Dec 2018)

ED: Publish as is (07 Jan 2019) by Marie Dumont

AR by Kathrin Naegeli on behalf of the Authors (17 Jan 2019)

Short summary

The paper investigates the temporal changes of bare-ice glacier surface albedo in the Swiss Alps between 1999 and 2016 from a regional to local scale using satellite data. Significant negative trends were found in the lowermost elevations and margins of the ablation zones. Although significant changes of glacier ice albedo are only present over a limited area, we emphasize that albedo feedback will considerably enhance the rate of glacier mass loss in the Swiss Alps in the near future.