Controls of outbursts of moraine-dammed lakes in the greater Himalayan region

Fischer, Melanie; Korup, Oliver; Veh, Georg; Walz, Ariane

doi:https://doi.org/10.5194/tc-15-4145-2021

Articles | Volume 15, issue 8

https://doi.org/10.5194/tc-15-4145-2021

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

https://doi.org/10.5194/tc-15-4145-2021

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

Articles | Volume 15, issue 8

Research article

|

30 Aug 2021

Research article |

| 30 Aug 2021

Controls of outbursts of moraine-dammed lakes in the greater Himalayan region

Melanie Fischer, Oliver Korup, Georg Veh, and Ariane Walz

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Final revised paper (published on 30 Aug 2021)
Preprint (discussion started on 16 Dec 2020)

Interactive discussion

Status: closed

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

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RC1: 'review to tc-2020-327', Adam Emmer, 13 Jan 2021
- AC1: 'Reply on RC1', Melanie Fischer, 16 Mar 2021
RC2: 'Review of the manuscript on Controls of outbursts of moraine-dammed lakes in the greater Himalayan region by M. Fischer et al.', Holger Frey, 20 Jan 2021
- AC2: 'Reply on RC2', Melanie Fischer, 16 Mar 2021

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (01 Apr 2021) by Tobias Bolch

AR by Melanie Fischer on behalf of the Authors (16 Apr 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (25 Apr 2021) by Tobias Bolch

RR by Adam Emmer (06 May 2021)

RR by Holger Frey (19 May 2021)

Suggestions for revision or reasons for rejection

The revised version of the manuscript is a clear improvement to the original version. The authors carefully prepared this revised version and complemented this with a detailed response letter, were they justify and explain their changes and arguments to the different comments raised. Namely they also invested considerable efforts in revising the figures and tables which definitely provide an added value now. In my view, this is now close to be acceptable, I only have a few, probably minor points that still need to by adjusted in my view.

My first general comment in the initial review was referring to the terminologies around hazard and susceptibility. Related adjustments in the new manuscript regarding this point are good and helpful, namely the consistent renaming of what was initially called “GLOF hazard parameters” or “diagnostics of GLOF potential” to now “predictors of GLOF susceptibility” is a clear improvement. The only point where I am not yet convinced is the statement in the conclusions (L481-482): “In any case, the widely adapted notion that (rapid) lake growth may be a predictor of impending outburst remains poorly supported by our model results”. In my view lake growth is not mainly considered as an outburst predictor in these assessments (i.e. a proxy for a high outburst susceptibility), but rather as a predictor of increased downstream hazard potential due to increased potential flood volume and thus hazard magnitude. I might be wrong, but since this statement is also used in the abstract, I would ask the authors to more clearly elaborate from the cited publications about these assessment schemes, if any why lake area changes are really considered as predictors of lake outburst susceptibility (rather than indicators of increased potential flood intensities downstream). This could be done, for instance, around L122 where it now says “and many studies have emphasised the role of growing lakes on GLOF susceptibility (Bolch et al., 2011; Prakash and Nagarajan, 2017; Rounce et al., 2016)”.

The second aspect where I am not yet 100% convinced is the point on using catchment area instead of lake area. The authors provide convincing arguments in their response letter and include this also in the revised manuscript (catchment area representing the potential of intense rainfall runoff and snow melt, as well as being invariant at the investigated time scales). But then I wonder why catchment area has not been used in all the models instead of lake area. Or why is this aspect more important for the glacier-mass balance model and the monsoonality model, an less for the elevation dependent and the forecasting model? In my view, a few more words on that would be needed, probably in the paragraph ending on L130.

Then also the reasoning of selecting “lake-area change” as a predictor (Table 2) as well as the response to my detailed comment #4 (lake depth, not area is determining the hydrostatic pressure on the dam) do not convince me yet. Most glacial lakes, once they have a certain size, mainly increase their area (and thus volume) but not their depth while the grow further. It is true that there are depth and volume estimation rules based on lake area, but the uncertainties of these approaches are huge, and they are based on empirical relationships (of static conditions) and do not involve any dynamic considerations, not any physical processes. If I think of any larger moraine dammed lake in the Himalayas that is growing due to glacier retreat at its upstream end (and thus increasing its area and volume), I would not expect a significant increase of lake depth. L119-121 and the reasoning in Table 2 should be reconsidered in my view.

Finally two more details on Table 1:
In the new Table 1, the predictors “glacial lake area” “lake-area change” should be moved from “lake characteristics and dynamics” to the “potential triggering mechanisms” group in my view. As the authors mention in the text and the response, lake area (increase) is a proxy for (increased) probability of the lake being impacted by an upstream mass movement.
Further, I think it is very unfortunate no reference is given for the “summer precipitation” predictor (last line in Table 1). Not that I could make a good suggestion, but having no reference here contradicts the study description (L72-73) “[…]we tested how well some of the more widely adopted predictors of GLOF susceptibility and hazard fare in a multi-level logistic regression […]”. Either some reference(s) should be added to this last line in Tab. 1, or a statement on the summer precipitation predictor should be made around this statement in the introduction.

The first three points require at least a few minimal adjustments in the manuscript. The details regarding Table 1 might also be explained and justified in a response if the authors prefer not to consider this in the manuscript.

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ED: Publish subject to minor revisions (review by editor) (01 Jun 2021) by Tobias Bolch

AR by Melanie Fischer on behalf of the Authors (10 Jun 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (22 Jun 2021) by Tobias Bolch

Dear authors,

Thank you again for thoroughly considering the comments. I am happy to accept the manuscript once the few minor comments below are addressed.

L. 36/37: Provide a reference for the statement.
L 48ff: You may also cite King et al. (2019) here as they specifically show that lake-terminating glaciers have higher mass loss in comparison to land terminating ones which has important implications for this study.
L. 89: Please add the correct citation for the RGI 6.0 (RGI Consortium, 2017. Randolph Glacier Inventory (RGI) – A dataset of global glacier outlines: version 6.0, Technical Report., Boulder, Colorado, USA.)
L. 90f and Fig. 1, Fig. 10: Please provide more details about the subdivision. It would be good to have consistency amongst the publications to allow comparisons. Did you use existing accepted subdivisions (e.g. as defined by Bolch et al. (2019) for the Hindukush-Himalayan Assessment report) or defined you own? The Nyainqentanglha region does not include the Eastern Nyainqentanglha. Adjust the name.
L. 122f: There are more publications addressing the changes of the glacial lake in the Himalaya and beyond, e.g. Wang et al. (2020) or Chen et al. (2021). Do the they come to similar findings than the study by Nie et al. (2017)?
L163: Provide the information about how you extracted the moraine-dammed lakes.
L. 410: You may want to consider that lake-terminating lakes have more negative mass balances and higher retreat rates than land terminating ones (King et al. 2019). Hence, the lakes are also growing faster.

Please do not hesitate in case you have any questions.

Best regards,

Tobias Bolch – Editor TC

References:
Bolch, T. et al. 2019. Status and change of the cryosphere in the extended Hindu Kush Himalaya region. In: Wester, P., Mishra, A., Mukherji, A. and Shrestha, A.B. (eds), The Hindu Kush Himalaya Assessment: Mountains, Climate Change, Sustainability and People. Springer International Publishing, Cham. 209–255.
King, O. et al. 2019. Glacial lakes exacerbate Himalayan glacier mass loss. Scientific Reports, 9 (1), 18145. doi: 10.1038/s41598-019-53733-x
Nie, Y. et al. 2017. A regional-scale assessment of Himalayan glacial lake changes using satellite observations from 1990 to 2015. Remote Sensing of Environment, 189, 1–13. doi: 10.1016/j.rse.2016.11.008
RGI Consortium, 2017. Randolph Glacier Inventory (RGI) – A dataset of global glacier outlines: version 6.0, Technical Report., Boulder, Colorado, USA.)
Wang, X. et al. 2020. Glacial lake inventory of high-mountain Asia in 1990 and 2018 derived from Landsat images. Earth System Science Data, 12 (3), 2169–2182. doi: 10.5194/essd-12-2169-2020
Chen, F. 2021. Annual 30m dataset for glacial lakes in High Mountain Asia from 2008 to 2017. Earth System Science Data, 13 (2), 741–766. doi: 10.5194/essd-13-741-2021

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AR by Melanie Fischer on behalf of the Authors (28 Jun 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (06 Jul 2021) by Tobias Bolch

AR by Melanie Fischer on behalf of the Authors (13 Jul 2021)

Short summary

Glacial lake outburst floods (GLOFs) in the greater Himalayan region threaten local communities and infrastructure. We assess this hazard objectively using fully data-driven models. We find that lake and catchment area, as well as regional glacier-mass balance, credibly raised the susceptibility of a glacial lake in our study area to produce a sudden outburst. However, our models hardly support the widely held notion that rapid lake growth increases GLOF susceptibility.