The Glaciers of the Dolomites: last 40 years of melting

Securo, Andrea; Del Gobbo, Costanza; Baccolo, Giovanni; Barbante, Carlo; Citterio, Michele; De Blasi, Fabrizio; Marcer, Marco; Valt, Mauro; Colucci, Renato R.

doi:https://doi.org/10.5194/egusphere-2024-1357

Preprints

https://doi.org/10.5194/egusphere-2024-1357

Preprints

18 Jun 2024

| 18 Jun 2024

The Glaciers of the Dolomites: last 40 years of melting

Andrea Securo, Costanza Del Gobbo, Giovanni Baccolo, Carlo Barbante, Michele Citterio, Fabrizio De Blasi, Marco Marcer, Mauro Valt, and Renato R. Colucci

Abstract. Small Alpine glaciers located below the regional equilibrium line altitude are experiencing considerable ice losses and are expected to fragment into smaller glacial bodies and eventually disappear. Monitoring such glaciers through remote sensing is often challenging because of the incompatibility between their size and the spatial resolution of satellites. The Italian Dolomites (S-E Alps) are a region clearly illustrating such challenges and where no long-term glacier mass balance data are available. This renowned Alpine sector hosted tens of glaciers up until a few decades ago, with now only twelve remaining. This study presents a multi-decadal (1980s–2023) estimation of surface elevation change and geodetic mass balance of the current mountain glaciers present in the area. Calculations are based on geodetic data: high resolution and accuracy is obtained with unmanned aerial vehicle (UAV) Structure from Motion (SfM) and airborne Light Detection and Ranging (LiDAR), from 2010 to 2023. SfM on historical aerial imagery is used for previous decades. We found an average cumulative surface elevation change of -28.7 m from 1980s to 2023, 33 % of which between 2010–2023. The average mass balance rate for the whole period is -0.64 ± 0.05 m w.e. yr^-1, varies significantly between sites, and is negative with a smaller amplitude than the Alpine reference glaciers mass balance. Regionally, 66 % of the entire volume loss is related to the Marmolada Glacier alone. Mass losses are accompanied by areal reductions evidencing that the Dolomites are rapidly losing their glaciers. This study aims to address the existing lack of multi-decadal data for the Dolomites by providing a quantitative account of the current state of these small glacial bodies.

Received: 07 May 2024 – Discussion started: 18 Jun 2024

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Journal article(s) based on this preprint

24 Mar 2025

The glaciers of the Dolomites: the last 40 years of melting

Andrea Securo, Costanza Del Gobbo, Giovanni Baccolo, Carlo Barbante, Michele Citterio, Fabrizio De Blasi, Marco Marcer, Mauro Valt, and Renato R. Colucci

The Cryosphere, 19, 1335–1352, https://doi.org/10.5194/tc-19-1335-2025,https://doi.org/10.5194/tc-19-1335-2025, 2025

Short summary

Andrea Securo, Costanza Del Gobbo, Giovanni Baccolo, Carlo Barbante, Michele Citterio, Fabrizio De Blasi, Marco Marcer, Mauro Valt, and Renato R. Colucci

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-1357', Anonymous Referee #1, 19 Jul 2024

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1357/egusphere-2024-1357-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2024-1357-RC1
- AC1: 'Reply on RC1', Andrea Securo, 27 Aug 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1357/egusphere-2024-1357-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-1357-AC1
RC2:
'Comment on egusphere-2024-1357', Anonymous Referee #2, 31 Jul 2024

Review of ‘The Glaciers of the Dolomites: last 40 years of melting’
By Securo, Andrea and others.
Securo and authors present a multi-decadal estimation of surface elevation change for small glaciers in the Dolomites, Italian Alps. Their geodetic data used in this study consists of aerial photographs, uncrewed aerial vehicles (uavs) and LiDAR data. This data and their analysis indicate high rates of glacier mass loss with the Marmolada Glacier accounting for about ⅔ of the region’s volume loss.
Overall, I found this manuscript to be generally well written with methods partially described. The presented data generally supports the conclusions made by the authors. However, like many papers, some clarification of the methods is needed, the English can be substantially improved and manuscript could be shortened. Below, I outline my major points about the paper and follow these with technical comments.
MAJOR POINTS:
1. Methodology and error analysis needs further description - Given that the authors are using multiple geodetic datasets to calculate volume (and mass) change, the methods section should clearly lay out how the actual uncertainties are propagated to yield the total error budget and final uncertainties. If I understand it correctly, the authors obtained point clouds from all datasets, align these and then use M3C2 for the error analysis. There has been some discussion about the robustness of M3C2 as it assumes planar surfaces and could estimate significance of detectable change (e.g. https://doi.org/10.1016/j.isprsjprs.2021.06.011). I would like to see, for example, how the uncertainty over stable terrain changes due to slope. These are small glaciers in rugged terrain so their slopes will be steep. Also, are there assumptions made for missing data? How is this error source treated?
2. Manuscript needs to be shortened/tightened - I found the ‘Introduction and Previous glaciological research’ sections to be long and would strongly advocate for merging the ‘Previous glaciological section’ with the Intro so that the total length of both sections is about ½ of what it currently is. Also, I think some of the tables could be moved to a supplement as most people rarely need to read each line of these tables (they are, however, useful to have if a reader needs them).
3. Comparison to previous work - The authors do a commendable job compiling datasets for these small glaciers, but they should explicitly show how their results compare to those, for example, of Hugonent and others (2021). The authors can download data for each of their glaciers (since each glacier has an RGI number this should not be a difficult task). How do their estimates and uncertainties compare to Hugonnet? This is an important test of the reliability of Hugonnet for small glaciers in this region (I would posit that perhaps the present study has better estimates for these small glaciers but I simply don’t know). It would be good to examine this in some detail.
4. Manuscript should be shortened. I found the length of the discussion section to be somewhat unbalanced with the length of the results section (the former is longer than the latter). I would recommend shortening the discussion section to balance in light of statements that can be backed up with results shown in the results section. Some of the figures/materials in the discussion seem, to me, to be more results and less discussion.
5. Terminology needs clarification - I would recommend that the authors consult the glossary for the standard definitions used in glacier mass balance (https://wgms.ch/downloads/Cogley_etal_2011.pdf) . There are multiple appearances of mass balance when the authors are referring to ‘geodetic balance’.

TECHNICAL COMMENTS:
Abstract:
‘Use lowercase ‘Alpine’ unless it starts a sentence.

Pg 1, Line 3: This sentence isn’t technically correct in light of Worldview or Pleiades (very high resolution)
Pg 1, line 11: ‘between used for two items, among for more than two’. Also use of ‘amplitude’ is vague
Pg1, line 13: replace ‘areal reductions’ with ‘area loss’
Pg1, lines 13-15 - This sentence is out of place and likely not needed
P1, line 18: ‘with greatest emphasis on regions of the world’ - unclear what authors are referring to here.
Pg 2, lines 25-33 - Authors could easily jettison this section to shorten first two sections that need to be put on a diet.
Pg 2, line 50 (and throughout) - ‘unmanned’ is an outdated term these days. Typical use is ‘uncrewed aerial vehicle’
pg.3 , line 63. Unclear what authors mean with ‘active’ - deformation, ice flow?
Section 2 - Shorten this section
Figure 1. The figure could use a little bit of work. The inset (upper left) needs at least some lat/lon coordinates for a reader not certain where the Dolomites are. I was initially confused with the color of the glaciers and the colors of the geodetic datasets (numbers). Maybe change the color of glaciers to avoid confusion? (a) - replace ‘position’ with ‘location’
Pg. 6, lines 115-118. Were these photos not available as photogrammetric scans? Also, it’s too bad that the internal orientation (if available) information isn’t used as that might help reduce overall error budget.
Pg, 6, lines 115-126. I had a hard time understanding how GCPs were collected and how they were used. This section should be revised to make it clear exactly what was completed and for which datasets.
Pg. 8, lines 153-154. I’m surprised that there were only small areas of voids. Was hypsometric interpolation attempted?
Pg 11, lines 210. Area change. How were areas of the glaciers digitized? Any uncertainty in area change? Unless I missed it, planimetric mapping is not described in methods.
Pg. 11, lines 219: Unclear what ‘topographic bounding’ is. Surrounded by rugged terrain?
Pg. 11, lines 228-229: Uncertainties needed for these estimates.
Pg. 13 lines 215: Terminology needs to be changed to include term ‘geodetic’
Figures 3, 4 - Generally well drafted, but uncertainties would be useful.
Tables 3, 4- I would recommend moving these perhaps to a supplement. Also it would be good to have a summary line for weighted mean (table 3). Does table 4’s all glaciers line imply this is a weighted mean (by area)?
Figure 5 - I think this is a well drafted figure, but I’m not fond of the color bar. It really should be a standard diverging color (red to blue). The dark ends for both red, blue are problematic for diverging data. Sorapiss Glacier’s mid elevation I presume is debris covered? I would explain before it is brought up in the discussion. As stated in the major comments, I think some of the discussion and plots should be moved to results section.
Figure 7. Not certain what color bars on top of the graph refers to. WGMS trend is the dashed line? It’s not evidently clear to me.
Pg 16, Results - How do these results compare to Hugonnet? Add those values perhaps to one of your tables with both estimates (yours and Hugonnet) including uncertainties.

Citation: https://doi.org/10.5194/egusphere-2024-1357-RC2
- AC2: 'Reply on RC2', Andrea Securo, 27 Aug 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1357/egusphere-2024-1357-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-1357-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-1357', Anonymous Referee #1, 19 Jul 2024

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1357/egusphere-2024-1357-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2024-1357-RC1
- AC1: 'Reply on RC1', Andrea Securo, 27 Aug 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1357/egusphere-2024-1357-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-1357-AC1
RC2:
'Comment on egusphere-2024-1357', Anonymous Referee #2, 31 Jul 2024

Review of ‘The Glaciers of the Dolomites: last 40 years of melting’
By Securo, Andrea and others.
Securo and authors present a multi-decadal estimation of surface elevation change for small glaciers in the Dolomites, Italian Alps. Their geodetic data used in this study consists of aerial photographs, uncrewed aerial vehicles (uavs) and LiDAR data. This data and their analysis indicate high rates of glacier mass loss with the Marmolada Glacier accounting for about ⅔ of the region’s volume loss.
Overall, I found this manuscript to be generally well written with methods partially described. The presented data generally supports the conclusions made by the authors. However, like many papers, some clarification of the methods is needed, the English can be substantially improved and manuscript could be shortened. Below, I outline my major points about the paper and follow these with technical comments.
MAJOR POINTS:
1. Methodology and error analysis needs further description - Given that the authors are using multiple geodetic datasets to calculate volume (and mass) change, the methods section should clearly lay out how the actual uncertainties are propagated to yield the total error budget and final uncertainties. If I understand it correctly, the authors obtained point clouds from all datasets, align these and then use M3C2 for the error analysis. There has been some discussion about the robustness of M3C2 as it assumes planar surfaces and could estimate significance of detectable change (e.g. https://doi.org/10.1016/j.isprsjprs.2021.06.011). I would like to see, for example, how the uncertainty over stable terrain changes due to slope. These are small glaciers in rugged terrain so their slopes will be steep. Also, are there assumptions made for missing data? How is this error source treated?
2. Manuscript needs to be shortened/tightened - I found the ‘Introduction and Previous glaciological research’ sections to be long and would strongly advocate for merging the ‘Previous glaciological section’ with the Intro so that the total length of both sections is about ½ of what it currently is. Also, I think some of the tables could be moved to a supplement as most people rarely need to read each line of these tables (they are, however, useful to have if a reader needs them).
3. Comparison to previous work - The authors do a commendable job compiling datasets for these small glaciers, but they should explicitly show how their results compare to those, for example, of Hugonent and others (2021). The authors can download data for each of their glaciers (since each glacier has an RGI number this should not be a difficult task). How do their estimates and uncertainties compare to Hugonnet? This is an important test of the reliability of Hugonnet for small glaciers in this region (I would posit that perhaps the present study has better estimates for these small glaciers but I simply don’t know). It would be good to examine this in some detail.
4. Manuscript should be shortened. I found the length of the discussion section to be somewhat unbalanced with the length of the results section (the former is longer than the latter). I would recommend shortening the discussion section to balance in light of statements that can be backed up with results shown in the results section. Some of the figures/materials in the discussion seem, to me, to be more results and less discussion.
5. Terminology needs clarification - I would recommend that the authors consult the glossary for the standard definitions used in glacier mass balance (https://wgms.ch/downloads/Cogley_etal_2011.pdf) . There are multiple appearances of mass balance when the authors are referring to ‘geodetic balance’.

TECHNICAL COMMENTS:
Abstract:
‘Use lowercase ‘Alpine’ unless it starts a sentence.

Pg 1, Line 3: This sentence isn’t technically correct in light of Worldview or Pleiades (very high resolution)
Pg 1, line 11: ‘between used for two items, among for more than two’. Also use of ‘amplitude’ is vague
Pg1, line 13: replace ‘areal reductions’ with ‘area loss’
Pg1, lines 13-15 - This sentence is out of place and likely not needed
P1, line 18: ‘with greatest emphasis on regions of the world’ - unclear what authors are referring to here.
Pg 2, lines 25-33 - Authors could easily jettison this section to shorten first two sections that need to be put on a diet.
Pg 2, line 50 (and throughout) - ‘unmanned’ is an outdated term these days. Typical use is ‘uncrewed aerial vehicle’
pg.3 , line 63. Unclear what authors mean with ‘active’ - deformation, ice flow?
Section 2 - Shorten this section
Figure 1. The figure could use a little bit of work. The inset (upper left) needs at least some lat/lon coordinates for a reader not certain where the Dolomites are. I was initially confused with the color of the glaciers and the colors of the geodetic datasets (numbers). Maybe change the color of glaciers to avoid confusion? (a) - replace ‘position’ with ‘location’
Pg. 6, lines 115-118. Were these photos not available as photogrammetric scans? Also, it’s too bad that the internal orientation (if available) information isn’t used as that might help reduce overall error budget.
Pg, 6, lines 115-126. I had a hard time understanding how GCPs were collected and how they were used. This section should be revised to make it clear exactly what was completed and for which datasets.
Pg. 8, lines 153-154. I’m surprised that there were only small areas of voids. Was hypsometric interpolation attempted?
Pg 11, lines 210. Area change. How were areas of the glaciers digitized? Any uncertainty in area change? Unless I missed it, planimetric mapping is not described in methods.
Pg. 11, lines 219: Unclear what ‘topographic bounding’ is. Surrounded by rugged terrain?
Pg. 11, lines 228-229: Uncertainties needed for these estimates.
Pg. 13 lines 215: Terminology needs to be changed to include term ‘geodetic’
Figures 3, 4 - Generally well drafted, but uncertainties would be useful.
Tables 3, 4- I would recommend moving these perhaps to a supplement. Also it would be good to have a summary line for weighted mean (table 3). Does table 4’s all glaciers line imply this is a weighted mean (by area)?
Figure 5 - I think this is a well drafted figure, but I’m not fond of the color bar. It really should be a standard diverging color (red to blue). The dark ends for both red, blue are problematic for diverging data. Sorapiss Glacier’s mid elevation I presume is debris covered? I would explain before it is brought up in the discussion. As stated in the major comments, I think some of the discussion and plots should be moved to results section.
Figure 7. Not certain what color bars on top of the graph refers to. WGMS trend is the dashed line? It’s not evidently clear to me.
Pg 16, Results - How do these results compare to Hugonnet? Add those values perhaps to one of your tables with both estimates (yours and Hugonnet) including uncertainties.

Citation: https://doi.org/10.5194/egusphere-2024-1357-RC2
- AC2: 'Reply on RC2', Andrea Securo, 27 Aug 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1357/egusphere-2024-1357-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-1357-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Reconsider after major revisions (further review by editor and referees) (02 Sep 2024) by Ben Marzeion

AR by Andrea Securo on behalf of the Authors (08 Oct 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (22 Oct 2024) by Ben Marzeion

RR by Anonymous Referee #1 (29 Oct 2024)

Suggestions for revision or reasons for rejection

I thank the authors for their responses to the comments and the thorough revisions. I find the overall clarity of the manuscript to be much improved. The error estimation has been expanded and is now more comprehensive.
I have a couple of very minor additional comments, which I believe can easily be addressed.

L135 Thank you for adding an explanation of “common area”. If I understand correctly, the “common area” will always be the area of the more recent time step, i.e. the smaller outline of the glacier in times of glacier retreat. Or are there cases in your data set where the more recent outline includes ground not covered by the older outline? Consider adding a short note to the explanation that indicates whether “common area” is always simply the smaller (more recent) area.

L150 "The contribution of uncertainties in area were not considered during this phase."
Okay, but please add a sentence or two justifying this and briefly acknowledge that this is a limitation of your uncertainty analysis, either here or in the discussion. Note that other studies using data of similarly high resolution do account for errors in glacier area, for example: Abermann et al (2010)
https://tc.copernicus.org/articles/4/53/2010/tc-4-53-2010.pdf
Fischer et al (2014):
https://www.tandfonline.com/doi/full/10.1657/1938-4246-46.4.933
Linsbauer et al (2021):.
https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2021.704189/full
All find an increase in area uncertainty with decreasing glacier size. You point out in the discussion (L343) that mapping is challenging depending on debris cover. You might mention uncertainty estimates by other studies here and give some indication of whether or not you feel that your mapped areas have a similar range of uncertainties.

L176 "The accumulation and ablation seasons were defined according to local climatology."
The authors explained what this means in their response to my previous comments. I think it would still be beneficial to add a sentence here and include this information in the manuscript. As in: Add a sentence stating that snow stations show increasing snow depth in the region between November and April (on average?) and this is how you defined the seasons.

Hide

RR by Anonymous Referee #2 (13 Nov 2024)

ED: Publish subject to minor revisions (review by editor) (11 Dec 2024) by Ben Marzeion

AR by Andrea Securo on behalf of the Authors (16 Dec 2024) Author's response Author's tracked changes Manuscript

ED: Publish as is (24 Jan 2025) by Ben Marzeion

AR by Andrea Securo on behalf of the Authors (29 Jan 2025) Manuscript

Journal article(s) based on this preprint

24 Mar 2025

The glaciers of the Dolomites: the last 40 years of melting

Andrea Securo, Costanza Del Gobbo, Giovanni Baccolo, Carlo Barbante, Michele Citterio, Fabrizio De Blasi, Marco Marcer, Mauro Valt, and Renato R. Colucci

The Cryosphere, 19, 1335–1352, https://doi.org/10.5194/tc-19-1335-2025,https://doi.org/10.5194/tc-19-1335-2025, 2025

Short summary

Andrea Securo, Costanza Del Gobbo, Giovanni Baccolo, Carlo Barbante, Michele Citterio, Fabrizio De Blasi, Marco Marcer, Mauro Valt, and Renato R. Colucci

Supplement

https://doi.org/10.5194/egusphere-2024-1357-supplement

Andrea Securo, Costanza Del Gobbo, Giovanni Baccolo, Carlo Barbante, Michele Citterio, Fabrizio De Blasi, Marco Marcer, Mauro Valt, and Renato R. Colucci

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We have reconstructed the multi-decadal (1980s–2023) cumulative mass balance for all the current mountain glaciers in the Italian Dolomites. We used historical aerial imagery, drone surveys and airborne LiDAR to fill the existing gap of glaciological data for the region. We observed an alarming decline in both glaciers area and volume, with some of them showing lower losses due to local topography and debris cover feedback. We strongly encourage more specific monitoring for these small glaciers.


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