|The authors have done a careful job to address the scientific issues that were raised in the first review. They have split the calculations between the northern and southern glacier, which behaved very differently, and they have analysed another KH-9 DEM which adds critical data in the accumulation area, making the mass balance calculations much more robust. They have also added four supplementary figures which give useful documentation for the most interested readers.|
However, I see two remaining issues before before publication:
1) The additional KH-9 DEM led to the discovery of a (potential) tributary surge. This is not sufficiently discussed and justified, and it raises concerns regarding the reliability of the overall mass balance which is highly dependent on zonal extrapolation. See my specific comments at L353 and L424 for details and suggestions.
2) Language. There are still numerous English errors and many sentences are unnecessarily complicated and logically wrong. This is disappointing for a second revision, and the authors cannot have put much effort into the proofreading. Naively, I started to make detailed edits/comments to bring it up to a minimum level, but really, this was a waste of time for me on something that should have been the authors’ job. Please take this more seriously in future submissions.
If these two issues and my comments below are sufficiently followed up, then I will recommend the paper for publication without another round of review.
L47: decreased → decades (?)
L49-50: Specify what kind of “shrinkage” you mean: area, volume or mass?
L51: What kind of “increase” are you talking about? The percentage numbers seem to actually indicate a slight decrease in shrinkage.
L108: What does the formula give for average precipitation then? No need to mention the formula unless you use it to something.
L101: It’s good that you provide coordinates, but how far away are they in km?
L115: Delete “the”
L122: Put the verbs earlier in the sentence.
L125: What does “finished-B” mean? Write out SRTM in full.
L131: Delet either “parts of” or “entirely”
L134-135: This doesn’t make sense unless you explain why.
L138: Write out HRG at least.
P186: Missing punctuation after sentence.
L190: Dependent on to → On the basis of
L191: was set to
L200: Remove space
L201: only SIG?
L205: with → as
L205: Uncertainty of what? Averaged velocities or local ones? If the latter, the uncertainty estimates seem too good.
L233-237: This is a long and unclear sentence that needs to be reformulated.
L242: It is not clear where the 20 m value comes from.
L247-261: It is unclear whether these estimated penetration depths are used to correct the SRTM DEM or if they are just used to estimate the uncertainty. If the former, then this paragraph belongs in the previous section. If the latter, then why?
L253: mean elevation difference within 100 m altitude zones
L255: Delete: according to each altitude zone (100 m)
L256: was discrepancy with → disagrees with the estimated
L259: Need a reference for that.
L272: insert comma
L273: GPS points
L276: How is the uncertainty estimated? As the mean absolute difference?
L277: Glacier melt can also be an elevation change. Simplify by removing sentence and adding “…, including glacier elevation changes between 2006 and 2009” to the previous one.
L280-286: I immediately understood the formula, but needed to read the text 5 times before I got the point. Always use terms like “glacier-wide” or area-averaged” elevation change when you talk about spatially averaged elevation changes. Please rewrite.
L287: the mean
L288: This answers my question at L247, but it should have come earlier. It is also unclear how the correction was done. Did you apply averaged values or the actual fields in Fig. S4? And since all penetration estimates are questionable - what would be the impact on the mass balance results if the entire correction was removed? It would be good to discuss that in a few sentences somewhere.
L293: But table 5 has rates (dh/dt)!? I don’t understand.
L294: If there is a lack of altitude zones, then there is no continuous glacier. Do you mean lack OF DATA in altitude zones?
L295-299: Firstly, it is very hard to understand what you have actually done, and secondly, I don’t see any justification for using (min+max)/2 in unmeasured areas. Why not just merge these altitude zones with the lower ones that have data, or simply set them to zero?
L299: dh/dt is an elevation rate, not a lowering rate (otherwise, the signs get wrong)
L304: Uncertainty was dealt with in the last section. I would switch the two sections and move this formula there (maybe removing the need for eq. 2). Regarding Eq. 3: How can you combine elevation uncertainties (unit m) with a density uncertainty (kg m-3)?
L318: This must be related to the deceleration of the tributaries then. The text doesn’t make any connection between the two pieces of information.
P335: Please don’t switch terms between mass loss and mass budget from one sentence to another when it involves opposite signs.
L337: An elevation is not thinning. It’s the thickness that thins. Delete “elevation”.
L337: Higher than what?
L340: Maybe. But in which way?
L341: Awkward wording: “analysis elevation differences measured”
L349: I would rather say ~0 considering the uncertainties.
L352: Very hard to spot the number 2 in Fig. 4a, and there is no explanation in the caption to point it out.
L352: It’s the velocity that was faster, not your measurement. Delete “measured”.
L353: Is it robust to interpret this as a surge? If the velocities were higher in 2002/03, one would rather expect thinning than thickening. You must be assuming a decelerating flow which would indeed cause thickening. But is it then a surge or a tributary stagnation? These things need to be discussed and clarified before claiming a surge. And what about zone 1? Doesn’t that look more like a fading surge considering the velocity fields?
L359: This is not an assumption, it’s clear.
L360: Any clue when the surge happened? Satellite imagery, literature, locals etc.
L362: What is a.s.l?
L362: Move “below 4300 m a.s.l.” to the entry that says a.s.l.
L366: To me it looks like slight thinning throughout.
L369: Again I don’t see a clear boundary at 4800 m a.s.l.. Very confusing.
L398: → the lower parts
L402: Be more specific, e.g. “…margin and enhances glacier mass loss”
L404: Refer to Supplementary Fig. 2
L405: “make up the short samples” → “fill data voids”
L406: See comment on L295. This just makes the paper unnecessarily complicated.
L407: Delete “weight of samples”, it just makes it harder to understand.
L408: effect → affect
L408: → “the area-averaged results (it adds <0.02 m a-1 of uncertainty)
L408: Remove figure reference.
L409: Very abrupt transition to other error sources. Rewrite and start with something like “Another source of uncertainty is the variable timing of the imagery…”
L419: decreasing → decreased. You don’t know if the mass loss was decreasing during 1999-2009! (you measure an average trend, not a change in trend)
L420: showed → show
L423: More interesting – do they show decreased mass loss in 1999-2007 like your results?
L424: “in disagreement” or “in contrast”? Important difference. The first suggest that one of the series is in error, the second suggest different glacier conditions.
L429: Did you do this analysis? It certainly cannot be seen from the figure in Gardner et al. 2013.
L431: Delete “obtained characteristics with a”
L433: How do you know it happened after 1990? From the Landsat image?
L437: Okay, but strange order of explanation wrt. L360 and L433. This review information fits better in Section 2 as an introduction to the study sites.
L441: Are you suddenly jumping from NIG to SIG?
L442: If you think this as a surge, then I have several requests for the paper: Fig. 5a should be expanded up the flow-line of the tributary to demonstrate the dh/dt characteristics before (1974-1999) and during/after the surge (1999-2007). This would hopefully give a much stronger support for your claim. Secondly, it raises the question whether the mass gain in this zone introduces a bias in the overall SIG mass balance since the likely thinning in the upstream areas is not captured and since the surge thickening gets extrapolated to unmeasured areas in the same altitude zones of the other tributaries. Can this explain why the 1999-2007 period is less negative than 1974-1999? You need to account for this or demonstrate that it does not impact the mass balance significantly.
L444: Before or during?
L445: Delete. It’s obvious and how a surge is defined.
L450: delete “was shown”
L453: Which way did the relationship go? Decreasing ablation with increasing thickness, I assume.
L458: You already said this in the previous sentence. No reason to repeat.
L461-466: Some basic statistics would be highly appreciated. Are the trends significant?
L482: Despite? A surge is a redistribution of mass, not a change in overall mass.
L490: distal → lower
L491: Delete “elevation”
L492: Commas after quicker and Merzbacher
Table 2: “With glacier free” → “glacier-free terrain” or “outside glaciers”. The two right columns give elevation values I believe, but it doesn’t say. Could be moved to supplement.
Table 3: “with GPS points to” → “between GPS points and”. Could also be moved to supplement.
Table 5: Area-average → area-averaged. I would put the rows in order of the periods as with the columns in Table 4. Also, SIG appears first in Table 4 and last in Table 5. Please find a consistent orders for all tables and figures.
Fig. 4: Make region 2 more visible in 4a, like done in Fig. 3.
Fig. 5: Expand 5a up along the flowline of the surging tributary. Include the years in the legend as for the other figures.
Fig. 6: Two things don’t seem right here: 1) 1999-1974 and 2007-1999 should add up to 2007-1999 except from altitude zones with very different data coverage. 2) There appears to be a clearly increased thinning below point b for SIG in 1999-2007. This seems to agree with Fig. 4a-b, but not Fig. 5a. How can that be?
Fig. S1: It is misleading that both high elevations and areas without SRTM have a white color. Several high-altitude white areas do have SRTM data id one considers Fig. 4.
Fig. S2: Nice figure, but I don’t understand the last sentence of the caption. Is it needed?
Fig. S3: VS → vs.
Fig. S4: Nice figure that almost deserves to be in the main manuscript. At least the debris-covered extent would be helpful for the discussion.
Fig. S5: of → between