the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 May 2024
Snow and glacier melt contributions to streamflow on James Ross Island, Antarctic Peninsula
Abstract. The Antarctic Peninsula is experiencing a rapid increase in air temperature, which has a major impact on the entire ecosystem, including the runoff process. Although water availability plays an important role in polar ecosystems, runoff generation in the Antarctic Peninsula region is still poorly understood. We analysed the variability in rain, snow and glacier contributions to runoff in relation to climate variability in a small, partly glaciated catchment on James Ross Island in the north-eastern Antarctic Peninsula. We used the hydrological model HBV to simulate the runoff process for the period 2010/11–2020/21 at a daily resolution. The model was calibrated against both measured discharge and glacier mass balance. Model simulations showed the negative mass balance of Triangular Glacier for 9 out of 11 study years with an average annual mass loss of 49 mm water equivalent. About 92 % of the annual runoff occurred between October and May. On average, peak runoff occurred in the second half of the summer season due to the combination of strong glacier and snow melt. The majority (76 %) of runoff originated from snowmelt, 14 % originated from glacier melt and 10 % from rainfall. The contribution of snowmelt to total runoff was higher in colder years with more precipitation. In contrast, glacier melt contributed dominantly during warmer years with less precipitation. Our simulation showed the presence of significant runoff-generating events outside the usual high summer runoff measurement season.
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RC1: 'Comment on egusphere-2024-1185', Anonymous Referee #1, 11 Jul 2024
General Comments
Overall, this manuscript is within the scope of the journal and adds some significant contributions to our understanding of the water budget and runoff processes on the Antarctic Peninsula. As I understand it, this paper is about quantifying the various contributions from snow, glacial melt, and rain to streamflow on the Antarctic Peninsula, and the relationships of total runoff and runoff contributions to climate variations. However, the title only mentions snow and glacial contributions but the paper also addresses rain contributions as well. There is also some confusion with the various study periods for the different model components as well as the field validations and measurements. The methods section needs more detail on the model: how the model uses the input data and how it estimates many of the simulated values, and also the field validation methods and what exactly was measured and how it was used. The discussion section also needs to be expanded in order to elaborate on the importance of the results and the implications for the ecosystems in this region and the effects of climate on runoff processes.
Specific comments
- ABSTRACT AND INTRODUCTION:
Lines 13-14: It would be helpful to actually state what the total study period is (i.e. June 2010 – May 2021).
Lines 17: What does “strong glacier and snow melt” mean?
Lines 25: What are “high air temperatures in recent years”? Can this be quantified above average or above previous maximum temperatures?
Line 40: It may be helpful to also note that all of the precipitation in the dry valleys is in the form of snow (whereas the peninsula also receives some rain, analyzed in this paper).
Line 55 and Line 62: It would be helpful to include some description of the terrestrial and marine environments in these regions in relation to streamflow and how they are affected by these runoff processes. What is the importance of understanding runoff processes for these ecosystems and environments?
Lines 66: Again the study period of 2010/2011 – 2020/2021 is confusing. It may be helpful to state that streamflow only occurs during XX months, so the study covers the time period of June 2010 – May 2021 or something along those lines…
- METHODS:
Lines 86-87: How much of the precipitation is estimated to come from rainfall and from snow each year? Has this changed over time?
Lines 70 and on… Some further discussion of the streams where discharge is being measured would be helpful. How much does the discharge vary from year to year? What is the average flow season? Is runoff only estimated at one location/stream?
Line 99: Why was 1 June estimated as the start of the water year?
Line 99: Were air temp and total precip the only inputs for the model? How does it use those to estimate runoff and glacier mass balance?
Lines 106: Was there any field validation for the simulated precipitation?
Lines 116: Why was the runoff only calculated from Feb – Mar 2018? Was there no other data outside this period? How did this period relate to the rest of the study period?
Lines 120: What is the “glaciological method”?
Lines 120-21: Why was surface mass balance only estimated for 2014-2020? These study periods don’t match up across the entire study and needs to be addressed.
Lines 125- 127: The section on snow depth needs more detail -- was snow depth only measured at one location? How was it extrapolated across the catchment? Is the snow on the glacier the only thing assumed to contribute to runoff ? What about snow in the rest of the catchment? Was SWE/snow density measured as well?
Lines 132: model routines need to be defined. Were all of these routines used? Or was one chosen from these 5?
Lines 146: Why was this section not considered in the model?
Lines 155-165: The runoff is reported in mm, but I assume it was measured in some rate (i.e. l/s). How was this rate converted to mm and why? Was it summed up over the daily, monthly, yearly period?
- RESULTS:
Lines 168 -171: These values could be put into a table to show the overall model fit.
Lines 176-177: Glacier mass balance simulation and observed should be included in Figure 2.
Lines 179-180: There was never a mention of SWE or snow density measurements in the methods. How was simulated SWE compared to snow depth? How did the model estimate SWE and snow depth? This needs a lot more detail in the methods and results.
Figure 3: The cumulative line in (a) should be a color that is easier to see (or does this line really need to be there?). The axes also need more values, especially at 0 in (a) to see mass loss or gain.
Lines 197: the glacier did not melt at all? Might be more appropriate to say “did not lose mass” as there was likely still some melt generated on the glaciers even if they did not lose mass.
Lines 198: Are these simulated SWE values? SWE measurements were never addressed in the methods section so I’m unsure if these values are from the model or measurements. If they are from the model, this needs to be added to the methods section of how the model calculates and estimates SWE.
Lines 202: What does it mean “these months accounted for 32% and 25% of the total SWE loss”? This needs to be explained more and likely shown in a figure.
Lines 204: The simulated mean runoff was 415 mm? Should this be 415 mm per year?
Lines 204-205: What were the instances when there was runoff outside of the main summer season? When did this winter runoff occur? This is brought up in the abstract and conclusion and needs much more attention in the results and discussion.
Lines 205: How was evapotranspiration estimated? This was never mentioned before in the methods.
Lines 206: It was never stated how much of the precipitation was estimated to come from snow vs. rain, or how the model partitions this. So how was the different contributions estimated between rain and snow in the model?
Figure 4: The axes should be colored for each of the values they are representing, it is confusing as is. Also, these should be split into two panels so that the various y axes don’t overlap. Precip and temp should be panel A with only one y-axis on each side. Panel B below should be Q and cumulative Q.
Figure 5: can these bars be stacked to add up to total Q instead of being side by side? That will make it easier to see how the allocation of various Q contributions changes.
Figure 6: Similar to Fig. 5 these figures are confusing and have too many axis values. It would be beneficial to split into panels so that the axes labels do not overlap.
Line 247: is this referring to snow cover on the glacier that melted out earlier?
Line 276: I am confused how Qglacier can be the only one significantly correlated with Q total, and how it can have the dominant control over total runoff, but Qsnow dominates the proportion of total runoff (over 75%)? This needs more in depth analysis and thought into what this means in both the results and discussion section.
Figure 9: It is hard to see the solid vs dotted circles, may want to make the outlines bigger or different colors.
- DISCUSSION:
Lines 304 – 305, should address the discrepancies in study periods for all of the data and how this may affect the interpretation of results.
Lines 316: Where did these percip measurements come from? From the methods, I thought that there were no precip observations so this needs to be addressed earlier. Are there measurements of both rain and snow?
Lines 326: So SWE was measured? Needs to be brought up in methods.
Lines 331: I thought this part was not considered in the model at all, but now it is saying that snow from this area was considered? Why is this? This needs to be explained more.
Lines 333 – 334: The statement “the glacier is covered with snow most of the year preventing any potential glacier melt” needs to be backed up. How does snow prevent glacier melt? Is there data to show that the glacier is actually covered with new snow most of the year? If there is no data or references to back this up than this statement needs to be removed.
Lines 349 – 350: What are the different definitions of the start year? Why was June 1 chosen for this study?
Lines 351-355: Why is this statement worth mentioning? If the authors feel that this is important to mention then this needs to be explained and elaborated on further here.
Lines 364-365: It is also important to note that the flow season for streams in the McMurdo Dry Valleys is much shorter than on the Peninsula, and most of the streamflow comes from glacial melt.
Lines 370: AP?
Lines 371 -372: The statement “this in turn may cause water shortages and affect local freshwater ecosystems” can be explained much more. How does water availability in these areas affect the ecosystems? Why is it important to study the runoff regimes of these areas for the environment and ecosystems? This needs references and elaboration to back it up.
Lines 373-374: How does rising temperatures influence suspended sediment transport? And what does this mean for this study? This section of the discussion needs to be expanded on quite a bit for the broader environmental implications.
Lines 376: Again, needs more expansion on the idea that higher amounts of rainfall can affect melting of snow and glaciers. How? And why is this important? Need references to back this idea up.
- CONCLUSIONS:
Line 391 – 392: the statement: “Together with mean annual evapotranspiration (7 mm) and mean annual precipitation (369 mm).” is not a complete sentence, maybe combine it with the previous sentence.
Lines 396: Again, what does “strong glacier and snow melt” mean?
Lines 398-399: as stated before, I am confused how Qglacier can be the only control on total annual Q, but Qsnow is the main contributor to Qtotal. This needs to be clarified in the discussion and if stated in the conclusion then it needs to be explained more.
Lines 404-405: The presence of runoff-generating events outside of the summer season was not addressed in detail in the discussion section, and if it is going to be included in the conclusion and abstract it needs much more attention and analysis outside of the brief mention in results.
Citation: https://doi.org/10.5194/egusphere-2024-1185-RC1 -
AC1: 'Reply on RC1', Ondrej Nedelcev, 31 Aug 2024
Thank you for the review of our manuscript. We appreciate your constructive comments and suggestions. Please find our point-by-point response in the attached file.
In general, we have identified the following main issues, which we have addressed below:
1) We found the method section related to a description of the HBV model (structure, routines, parameters) too brief and we will describe it in more detail.
2) We will be more explicit about the data used for model calibration and simulation. In particular, we will clarify how the discharge, glacier mass balance and snow data have been used to model calibration and evaluation
3) We will better explain how the runoff components are calculated in the model and how to interpret the results related to the inter-annual variability of the components and explain the contradiction between the snowmelt which contributes most to the total runoff and glacier-melt which controls the inter-annual variability.
4) We agree that more emphasis should be placed on a literature review and discussion related to understanding the runoff process in polar areas and its impact on terrestrial ecosystems.
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RC2: 'Comment on egusphere-2024-1185', Rijan Kayastha, 20 Jul 2024
The manuscript is well written and good to publish in the journal. My main concern is about the degree-day factors used in the study. Therefore, my specific comments are as follows:
Line 132-133: It is good that the degree-day-based snow melt and glacier melt modules were used in the HBV model. It is necessary to mention whether the degree-day factors are model-calibrated or assigned values derived from the field measurement in the past. Since the degree-day factors play a significant role in the ablation estimation, it should be mentioned degree-day factors in this study. Moreover, sometimes model-generated degree-day factors may be unrealistic. Therefore, I suggest mentioning degree-day factors used in this study.
Line 347: It should be …. was also slightly negative in 2014/15, ……………..
Line 435: Missing the reference of Seibert and Vis (2012).
Citation: https://doi.org/10.5194/egusphere-2024-1185-RC2 - AC2: 'Reply on RC2', Ondrej Nedelcev, 31 Aug 2024
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