the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Nov 2023
Brief Communication: Recent estimates of glacier mass loss for western North America from laser altimetry
Alex Gardner
Caitlyn Forentine
Andrew Fountain
Abstract. Glaciers in Western North American outside of Alaska are often overlooked in global studies, because their potential to contribute to changes in sea level is small. Nonetheless, these glaciers represent important sources of freshwater, especially during times of drought. Differencing recent ICESat-2 data from a digital elevation model derived from a combination of synthetic aperture radar data (TerraSAR-X/TanDEM-X), we find that over the period 2013–2021, glaciers in western North America lost mass at a rate of -12.3 ± 3.5 Gt yr-1. This rate is comparable to the rate of mass loss (-11.7 ± 1.0 Gt yr-1) for the period 2018–2022 calculated through trend analysis using ICESat-2 and Global Ecosystems Dynamics Investigation (GEDI) data.
- Preprint
(3494 KB) - Metadata XML
-
Supplement
(136 KB) - BibTeX
- EndNote
Brian Menounos et al.
Status: open (until 25 Dec 2023)
-
RC1: 'Review of egusphere-2023-2408', Erik Mannerfelt, 15 Nov 2023
reply
The authors present a new regional geodetic glacier mass balance estimate for western North America using well established methods to a study area and rationale that ensures its novelty. They argue the use of the analysis well; similar studies have already been performed but their source of data (ASTER) will not be available for many more years. Therefore, we need a new source for monitoring regional mass balance, and the authors present the solution well.
Generally, the text is concise and well-written. My comments are only textual edits, and I therefore recommend this paper for acceptance after correcting them. Some comments on the figures could either be typos, misunderstandings by me, or actual issues with the plots. Therefore, I chose "minor revisions" instead of "technical corrections" as I presume that gives some more time to fix these (potential) issues.
General comments:
The tense is slightly inconsistent in the text. At L41, “we use”; first person present. At L55, “we reprojected”; first person past. L63: “was buffered”; third person past. Please look over the text and pick one for consistency.
The two figures are generally very informative! They can be improved to make them even better in terms of labeling, and the second figure has an unclear distinction between two black lines. I elaborate on this in my specific comments below.
Is there a good reason for the data will not be made available online? The per-RGI values and rates would certainly be useful in other studies! I wholeheartedly recommend making the data available through e.g. Zenodo, and preferably the code too. I will however leave it up to the editor whether my recommendation should be enforced or not.
Line-specific comments:
L33: “Recent studies” imply multiple studies, but only one is referred to. If there’s only one, I suggest rephrasing the sentence. For example, “but the glaciers of western North America have so far been excluded from global laser altimetry assessments (Jakob and Gourmelen, 2023).”
L33-34: Why was western North America excluded by the cited paper? It is previously mentioned in the text and also mentioned in Jakob and Gourmelen (2023), but the sentence is missing a word or two, as it right now looks like an arbitrary decision by the authors of the cited paper. Honestly, their own rationale is a bit arbitrary (“[…] particularly challenging to capture with radar altimetry, including […] USA […]”; challenging how?). If another sentence is added to this manuscript, I think it would read better. Perhaps you can speculate that they excluded it from a cost-benefit perspective (it’s “challenging”, but again, why?, and it does not contribute that much to global sea level rise), as the US would not improve their results much. Or there is a good reason why they did it, but you think you can do better?
L40: I first misread the 88 degree N/S statement to be the inclination of the orbit. If you added “in latitudes” before “between” I think it would read better.
L44: Same comment as L40: I recommend specifying “latitudes between 51.6° N/S”.
L55: Which UTM zone and which coordinate system? There are many other coordinate systems with UTM zones. You can add a parenthesis for it “(WGS84 UTM Zone XX N)”.
L58: Replace the comma of “[m], rates of […]” with an “and”.
L60: Surges may occur that exceed +20 m/a at their termini! Please add a sentence explaining that you assume this to improve the total uncertainty using this filter, in spite of maybe accidentally filtering out extreme true values on surges at individual glaciers. Or if you qualitatively checked extreme areas and found that the filter was okay, please add this instead.
L63: This is the first time the abbreviation RGI is used. Please explain it here or add the abbreviation to L36 where Randolph Glacier Inventory is spelled out.
L64-65: Please elaborate on how you can certainly consider the surrounding terrain stable. For example, if the bedrock is generally stable and most (all?) glaciers are surrounded by bare rock. What about vegetation and lakes? Is ICESat-2 and GEDI all robust to that? If you qualitatively saw that lakes and vegetation don’t seem to be an issue, that would be okay for me to state too.
L65: Are the RGI or GLIMS ids the same as well? If not, it would require some work to use your data in the future.
L70: Add “c.f.” to the Enderlin reference if you actually inspected this yourself too.
L80: Again, I would argue that 150 m from a median anomaly is realistic in extreme cases on surges. Please argue for why this is (hopefully) not relevant. If you feel like this has been argued enough for in my L60 comment, I welcome you to ignore this one. Basically, if you at some point establish that surges will be a source of uncertainty (or are they rare enough?) and you exclude their consideration, none of this would be a problem to me.
L83: Please rephrase “This did not disrupt the representation of glacier hypsometry” as the reader does not know how you know this. For example, starting with “We did not find a considerable disruption […] due to these criteria”
L88-94: I’ve never seen this approach before to include uncertainties in time. I like it! It does sound computationally expensive for large regions, however. Do you have a computation time statistic to support or discourage using the same method on equally large or larger regions?
L96: I would personally stay consistent with the use of “uncertainty” instead of “error”, as we have no idea what the real value is, and the word error can thus be misleading.
L103: “we limit our analysis” reads more like the methods section. If you don’t want to move the sentence, I suggest changing it to “we limit the presentation of our analysis” or something like it to be more in line with a results section.
L112-113: A word or two is missing here: “[…] recent period), glaciers lost”. For example, if the sentence started with “Figure 2 shows that when using only […]”, the problem would be fixed. Alternatively, consider splitting the sentence in two.
L114: “elsewhere” sounds vague. Consider changing it to “the supplementary material”.
L114: A word is missing or the tense is wrong. “the effect of a small sample size” or “the effect of small sample sizes” would read better.
Discussion and conclusion: Please add a sentence (perhaps in the very end), that your results are consistent in both magnitude and uncertainty to previous estimates using instruments (i.e. ASTER) that will soon be unavailable. Your approach therefore “secures” our need for continued up-to-date information in the future.
Figure 1 caption: “Data are aggregated […]” will make the second sentence read better.
Figure 1 caption: To be consistent with the text, with Figure 2, and with most other publications, I would suggest switching the years to “2013-2022” instead of “2022-2013” (and with all similar occurrences).
Figure 1: The forward slash (e.g. “ICESat-2/COP-30”) reads a bit like there’s division going on. I presume that this is because of the hyphens in the product names, but I would suggest trying out an en-dash or the word “to” for clarity.
Figure 2 caption: Why is this 2013-2021 while Fig. 1 is 2023-2022? If there is a good explanation and this is not a typo, please elaborate in the caption to make it easier for the reader.
Figure 2: Please change the legend labels to be more readable and consistent with the text and Figure 1. “Copdem30” → “COP-30”, “rgi_glaciers” → “RGI glaciers”.
Figure 2: It looks to me like the “rgi_glaciers” and “IS2 shots” lines are offset horizontally by, say, half a bin. Is this an error? If not, please disregard this comment.
Figure 2: The elevation change and “rgi_glaciers” lines are very similar. I would recommend changing one of these lines’ color to make the legend and the plot easier to understand.
Citation: https://doi.org/10.5194/egusphere-2023-2408-RC1
Brian Menounos et al.
Brian Menounos et al.
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 92 | 44 | 5 | 141 | 8 | 2 | 1 |
- HTML: 92
- PDF: 44
- XML: 5
- Total: 141
- Supplement: 8
- BibTeX: 2
- EndNote: 1
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1