This paper is substantially improved from the previous version. I concerned about too much complicated data screening process in the previous manuscript, but now the methodology is simplified and presented in a more understandable way. Uncertainties in the results are very carefully analyzed, which enabled quantitative discussion on the three main research questions, acceleration in glacier thinning, spatial patterns and influence of debris cover, and the impact of the 2015 earthquake. The results are described in detail with carefully prepared plots and tables. The discussion and conclusion are useful not only for researchers on Himalayan glaciers, but also those who uses same techniques for glacier surface elevation change.
I understand that the authors tried to describe the work very carefully. However, in my opinion, it contains too much detail. For example, ALOS PRISM image is listed and described as satellite data used in this study, but actually they did not use it in the analysis and explain why they were excluded. Detailed and frequent descriptions on the uncertainty often get into the way of understanding of more important subject. It is tough to read and try to understand every detail, which are not necessary to catch the main points of the paper. I also think the text is lengthy in general. The manuscript will be improved by using simpler and more straightforward expression. I also find several paragraphs are not in a right position. For example, starting Result section with the impact of 2015 earthquake is odd, because it forms the third main research question and occurred at the end of the study period.
Below, I list my comments and suggestions for consideration by the authors to improve the paper before publication.
page 1 Abstract:
>> Abstract is too long. Please focus on the main points.
page 3, line 29 – page 4, line 6:
>> This paragraph should be merged to the next paragraph. Instead, here you can describe more about the advantages and problems of satellite derived DEMs and mass change measurements by DEM differentiation. This is because substantial portion of the text, figures and tables are dedicated to uncertainty estimation.
page 5, line 27:
>> Please consider to exclude ALOS PRISM from the text because it is not used for the analysis.
page 6, line 24: dGPS
>> Please make sure that the term "differential GPS" is correctly used. It is something different from static or kinematic survey with two receivers.
page 7, line 2: 17 GCPs
>> 17 GCPs off the glaciers?
page 11, line 22: 850 kg m-3
>> Do you use this density in the ablation area and debris covered regions?
page 12, line 28: an automated flow accumulation process
>> What is this?
page 14, line 2: using a window size of 128 down to 32 pixels,
>> What do you mean? "between 128 and 32 pixels"?
page 14, line 16-21: To calculate the deposited volumes ….
>> Do you mean that "Volume change due to the earthquake by subtracting mean thinning rate between Oct 2006 and Feb 2015 from the volume loss between April 2014 and April 2015."?
4.1. Impacts of the April 2015 earthquake:
>> It is odd to have this subsection in the beginning of this section. It is better described at the end of Results section as 4.5, because it addresses the third main research question (page 4, 12-14) and it occurred at the end of the observation period.
page 15, line 4: Field visits
>> Field visits to which glacier?
page 15, 8-19:
>> I do not understand why October 2015 DEM was used for the 2006-2015 ensemble but May 2015 DEM was not considered. DEMs in May and October 2015 are both influenced by the avalanche by the same amount of 1.31 m. The deposition in October is less than that in May. This is just because it spent one ablation season, and it does not mean the October 2015 DEM is less influenced by the avalanche. I suggest the author to exclude all the DEMs after the earthquake to compute the 2006-2015 ensemble.
page 15, line 30 – page 16 line 6: The error bounds….
>> This is an example that too much detailed description on the uncertainty gets into the understanding of more important points. Please consider to move this kind of details to supplementary information if necessary.
page 16, line 8: At Shalbachum Glacier the error bounds are overlapping but the estimated probability that 1974-2006 thinning rates are higher than 2006-2015 volume loss rates is less than 10%.
>> "At Shalbachum Glacier the error bounds are overlapping but the estimated probability of thinning acceleration is more than 90%."
page 16, line 13: The estimated probability that at one of these glaciers mean thinning rates changed by less than ± 0.15 m a-1 between the two periods is higher than 90%.
>> "Mean thinning rates of these glaciers changed by less than \pm 0.15 m a-1 between the two periods (90% confidence)."
page 16, line 17-20: "The ensemble uncertainty is ± 0.43 m a-1, which …"
>> Please consider to omit these sentences because they are not essential to draw your main conclusions.
page 16, page 29: An increase in identified mean volume loss rates…
>> An increase in volume loss rates …
page 16, line 31 - page 17, line 2: For Ghanna tongue the identified changes in thinning rates are not significant given the uncertainties, …
>> "Changes in thinning rates are not significant for Ghanna tongue, but five out of six members of the 2006-2015 decreased as compared to the previous period. "
page 17, line 11-13: Here, the 2006-2015 ensemble mean value (-0.50 ± 0.20 m a-1) indicates more than three times lower thinning rates than at Lirung tongue.
>> " Here, the 2006-2015 ensemble mean value (-0.50 ± 0.20 m a-1) is 30% of the thinning rate at Lirung tongue."
page 17, line 25-28: Our analysis thus shows that elevation change estimates are in most cases not significantly different if we assume different thresholds for outlier definition or if we consider the uncertainty in our ELA estimate.
>> "Our analysis thus shows that elevation change estimates are in most cases not significantly influenced by outlier definition and ELA estimate."
page 17, line 28-30: Significant sensitivity values …
>> Please rewrite. e.g. "Erroneous patterns in the accumulation areas (> 1 sigma) cause significant influence on the results."
page 18, line 10: This pattern of decreasing thinning rates contrasts…
>> "This pattern constrasts…"
page 18, line 12-13: "… the comparability of 1974-2006 12 thinning rates with the 2006-2015 ensemble is limited."
>> What do you mean? "thinning patterns in 1974-2006 and 2006-2015 are different"?
page 18, line 23: To compare the thinning patterns of debris-covered glaciers to the thinning patterns of debris-free glaciers, …
>> "To compare the thinning patterns of debris-covered and debris-free glaciers, …"
page 18, line 25-26: Yala Glacier experiences more rapid thinning over almost its entire elevation range in recent periods.
>> " Yala Glacier experiences more rapid thinning in recent periods over almost its entire elevation range."
page 19, line 5-11:
>> Please consider to rewrite this paragraph.
page 19, line 8-9: "the difference between thinning near the terminus and maximum thinning"
>> It is not clear what is meant by "difference".
page 19, line 10: "but"
>> I do not understand why these two clauses are connected by "but".
page 20, line 18 – page 21, line 27:
>> Please consider to move these paragraphs to Discussion section. You describe more than "Results".
page 21, line 19: Lirung tongue also shows an opposite behavior, except for the lowest elevation band.
>> It is not clear what is meant by "opposite behavior".
page 21, line 25: "not stagnating"
>> Please consider to reword it.
page 21, line 27: …we observe stagnant conditions with velocities below 2.5 m a-1.
>> "… we observe velocity below 2.5 m a-1."
page 22, line 16-19: "Accelerated thinning …"
>> It is difficult to understand this sentence.
page 23, line 18-20: "However, given the usually very slow dynamical response of debris-covered glaciers to changes in the local temperature (Banerjee and Shankar, 2013),"
>> I do not understand why this can be a reason why "slowdown of the compressive flow regime is not the primary factor".
page 23, line 30: loose
>> lose?
page 24, line 6-7: "It can thus be assumed that they become less abundant with decreasing flow."
>> Are you sure that this is true on debris covered glaciers in general?
page 24, line 21: 5.1.1 Post-earthquake avalanche impacts
>> I suggest the author to move this subsection to the last in Discussion.
page 26, line 32: 2011), " our results indeed point to a difference in current volume loss of debris-free and debris-covered glaciers."
>> It is not clear what you mean.
Table 4 caption: " … due to avalanches triggered by the Nepal earthquake on 25 April 2015."
>> It is not accurate to attribute all the changes to the earthquake because they include the effects of mass balance and ice flow for a certain amount. What about writing as "… after the earhquake on 25 April 2015"?
Figure 2:
>> I suggest the author to move this plot to supplementary information. This is too much detail to show in the main text.
Figure 3:
>> Please explain in the caption what do the color bars represent.
Figure 13: "Off-glacier velocities are shown in transparent color."
>> I do not think this information is necessary on the plot. |
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