Seasonal discharge response to temperature-driven changes in evaporation and snow processes in the Rhine Basin

Buitink, Joost; Melsen, Lieke A.; Teuling, Adriaan J.

doi:https://doi.org/10.5194/esd-12-387-2021

Articles | Volume 12, issue 2

https://doi.org/10.5194/esd-12-387-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/esd-12-387-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 12, issue 2

Research article

|

08 Apr 2021

Research article |

| 08 Apr 2021

Seasonal discharge response to temperature-driven changes in evaporation and snow processes in the Rhine Basin

Joost Buitink, Lieke A. Melsen, and Adriaan J. Teuling

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Final revised paper (published on 08 Apr 2021)
Supplement to the final revised paper
Preprint (discussion started on 13 Oct 2020)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'review', Anonymous Referee #1, 26 Oct 2020
- AC1: 'Reply to AR1', Joost Buitink, 19 Nov 2020
RC2: 'review', Anonymous Referee #2, 29 Oct 2020
- AC2: 'Reply to AR2', Joost Buitink, 19 Nov 2020
RC3: 'review', Anonymous Referee #3, 07 Nov 2020
- AC3: 'Reply to AR3', Joost Buitink, 19 Nov 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (26 Nov 2020) by Gabriele Messori

AR by Joost Buitink on behalf of the Authors (07 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (08 Jan 2021) by Gabriele Messori

RR by Anonymous Referee #3 (17 Jan 2021)

RR by Anonymous Referee #1 (18 Jan 2021)

Suggestions for revision or reasons for rejection

Seasonal discharge response to temperature-driven changes in evaporation and snow processes in the Rhine basin
Buitink et al. 2020: https://doi.org/10.5194/esd-2020-73

General comment
The manuscript considerably improved compared to the other version I saw. The text is structured better and the model set-up explained better. In the following, some more minor issues that should be addressed before it is considered for publication. When specifying line numbers, I refer to the marked-up manuscript.

Specific comments:

Structure text: Even though the structure of the text is better now, one more revision is necessary, in my opinion. There still are some elements in the result section that should be moved to the method part. Please discuss your results in the 'Discussion'. Still almost all the discussion is in the result section. Add sub-section to the discussion (preferably the same that you use in the results).

Line 8: Please explain (what you mean by combination of these variables.

Line 19-20: Suggestions:: write directly 'less precipitation and lower snowmelt rates' and remove 'potentially higher snowmelt rates' and 'surprisingly'.

Line 61: expected > potential

Fig. 1: You detect less precipitation in the second time window. How do you explain this? Before you mention the intensification of the hydrological cycle. Should this cause more precipitation? Or is it just decadal variability?

Line 125 ff: The model does not include lakes or reservoirs, as far as I understood. This should be mentioned here and discussed later, as this is important for low flow situations.

Line 139: You run in hourly resolution, right? How does this work when you have a degree-day approach? What glaciers do you simulate? How does the model know that there is ice to simulate in a pixel? In case the snow and glacier modules are new, their impelentation should be explained a bit better, I think.

Line 156: Please provide references of other studies using this swapping approach and discuss (dis-)advantages better.

Line 171: Please explain better what you mean by 'interaction between the three forcing components. This is an important point of your study and should be explained in more detail, I think.

Line 180: You add 0.5 ° to you hourly temperature time series? If yes, please discuss possible shortcomings of this approach.

Line 198-199: This information needs to be in the method section.

Fig. 3: How do you determine that differences are significant? Significant differences in median values?
LIne 205-209: Move this information to the section on data and methods. Do not introduce new data of validation approaches in the result section.

Line 210: Please explain why you use this catchment.

Line 240: 'ice' Glacier melt during March and May? Can you check whether it really is snow + ice or only snowmelt?

Fig. 4: To me it is confusing why there are two ylab next to panel d. Please move to correct panels.

Line 246-249: I do not understand this explanation. Why are 'storage conditions' different between the months of March and April?

Fig. 3: Please provide an explanation for the almost sinusoidal variation in your result figures.

Line 267-269: Ho is it possible that you get opposite results in your experiments for Jan-Feb with regard to changes in snowmelt contribution. I am surprised as well. Please explain better

Line 269 and Line 351: 'snow processes': Please specify what you mean by snow processes. Is it accumulation, snowmelt rates, timing,...

Line 285: Move to discussion. Please do not discuss you results in the result section. Discuss in Discussion.

Line 297: 'Over these periods of 10 years, most interannual variability is average out'

Line 348: I still have troubles to understand how you get to this number of 19 % for precipitation. Please explain in the method section.

Line 351: It sounds like there is more snowmelt with higher temperatures in Sep-Oct. Is this what you want to say? Isn't it the opposite? Higher temperatures result in a reduction of snow accumulation and a reduced build up of a snow cover. Rainfall is liquid instead of solid and hence more runoff?

Line 264: Where do you snow enhanced snowmelt in you study? I do not see a figure depicting changes in snowmelt (rates) in you study.

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RR by Anonymous Referee #2 (18 Jan 2021)

Suggestions for revision or reasons for rejection

I do not think the increase in discharge due to increased snow melt (processes) is a major conclusion. Suggesting that it partially offsets reductions in discharge is misleading. It seems that if you added up the increases during colder parts of the year with the decreases during warmer parts, they would equal 0 and changes in snow melt (processes) would not have much impact?

Abstract: This is still confusing to understand what was done in this study. I highly recommend using the term snowmelt throughout the paper as a simple and consistent replacement for “snow processes” or “snow dynamics”.
L1-6: “… how temperature-driven changes in evaporation and snow processes influence the discharge”. Fourth sentence: “… observed changes could be explained by the changes induced by snow, evaporation and precipitation”. I would try to make these sentences consistent. Mention specifically in the first sentence which parameters influenced discharge. Further, there are many snow processes, I would just mention the ones in your model that effect discharge (i.e. snowmelt (including glacier melt)). I am confused with attributing some changes in discharge to snow and precipitation. Snow is precipitation, so is it included in precipitation? Or do you mean liquid precipitation?
L6: Changes in precipitation explained more of observed changes in discharge than changes in snow or evaporation, but in the title and throughout the paper you focus on evaporation and snow processes. Why are changes in precipitation left out of the title and not mentioned throughout the paper when changes in snow processes and evaporation are?
L7: Higher temperatures led to earlier snowmelt (faster winter snowmelt rates) and less available snowpack to melt later in spring, when it historically melts.
L16: Need a reference for “potentially higher snowmelt rates”. Perhaps you are talking about an increase in winter snowmelt rates? (“Melt trends portend widespread declines in snow water resources”)
L17-18: This new sentence comes off out of place without additional context.
L20: “Water towers” were defined earlier “Mountains of the world, water towers for humanity: Typology, mapping, and global significance”. Also, add “to” between important and have.
L26: Wouldn’t only melted snow affect discharge?
L50: I am more of a fan of using the term “snowmelt” compared to “snow processes”
L64: Delete “upstream of the basin”.
L149-150: How do you separate temperature effects on ET or snow processes? Wouldn’t changing the temperature affect both processes at the same time? Are you only changing temperature during the winter/summer and attributing that to only affecting snow/ET?
L244: What do you mean by snow and evaporation are threshold processes?
L246: add “periods” between ‘the’ and ‘during’
L248: “Partially offset” seems like a stretch for the Jan-Feb period. The black line barely deviates from the orange line.
L266: Switch “changed” to “change”
L324: Can you differentiate between snow melt and ice melt?
L330-331: Can this be explained with your data? Yes, the blue line in Fig. 5a is often barely above the dashed black line, but I would not rely on it too much. This statement is misleading if you cannot differentiate between snow and glacier melt and presents a potential false hope.

Referee Report: PDF

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ED: Reconsider after major revisions (19 Jan 2021) by Gabriele Messori

AR by Joost Buitink on behalf of the Authors (05 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (15 Feb 2021) by Gabriele Messori

RR by Anonymous Referee #2 (15 Feb 2021)

Suggestions for revision or reasons for rejection

I think the addition of Figure S4 is very helpful for interpreting the results, but would like to see more discussion put into the ‘offsetting’ effects of increased snow processes throughout the majority of the year and more of an attempt to disentangle the effects from snowmelt and glacier melt. For example, in the supplementary you show decreases of snow storage (S3), snow cover (S3), and snowmelt rate (S4) with increasing temperature, but increasing glacier melt (S4) (it would be better if S3 and S4 had the same range for x-axis for easier comparison). Grouping snowmelt and glacier melt into the same term is misleading as they represent two water storages with very different residence times and thus different consequences of ecosystem vulnerability to warming scenarios.
• The results from Figure S4 imply the increase in Jan-Feb discharge (Figure 5b, 6a) is caused by increases in glacier melt, since snow melt rates decrease during this time (and all times). Is this correct? Based on the larger magnitude of glacier melt during the summer from Figure S4, I would have expected larger changes in discharge to occur in the summer (i.e. more blue pixels during May-Jun and Sep-Oct compared to Jan-Feb).
• Why do increases in discharge occur from snow processes during Jan-Feb (Figure 5, 6a) if snowmelt rate decreases during this time and glacier melt is close to 0? Can you rescale the y-axis in Figure S4 so that each plot is comparable (i.e. averaged over the entire basin)?
• Based on the results from Figure S4, the offsetting effect is solely due to increased glacier melt, as snowmelt is shown to decrease under warmer scenarios for all months. This needs to be discussed more as the water stored in glaciers is finite, thus this offsetting effect will be eliminated under warmer scenarios when the glaciers have completely melted.

L11: Please specify what an interaction of the variables means in the abstract since more than half of your results are due to the interaction and understanding the interaction is vital.
L14: When applicable, please mention whether the ‘changes’ are positive or negative. Switching the language to ‘increases’ or ‘decreases’ would ease in interpreting the main results. You use the terms ‘changes’ and ‘differences’ throughout the manuscript and it would be easier to interpret if you clarify if they are positive or negative changes.
L14 / 386: This is still one of my biggest concerns in regards to interpreting your results. Again, I think the term ‘partially offset’ is misleading as discharge clearly decreases due to increases in evaporation and the increased snow processes barely make a difference. Also, be consistent of what the low flow period refers to. Earlier in the manuscript lowflow referred to Sep-Oct, now you are including Nov too. I feel that the main take-away from the second experiment (Figure 5), which should be emphasized more in the abstract and conclusion than the offsetting from snow processes, is that simulated discharge is lower in every month and primarily caused by increases in evaporation.
Further, since these results do not distinguish between snow melt and glacier melt, this is problematic if most of this offset is due to glacier melt (as indicated by S4), which is a finite supply of water, thus will eventually disappear given enough warming. I think you should clarify that this ‘offsetting’ will not occur in future warmer scenarios when the glaciers are depleted and more precipitation falls as rain compared to snow.
L201: Rewrite “For example, temperature and precipitation are linked as the type of precipitation (rain or snow) is dependent on temperature.”. It is still confusing what the interaction of the forcing components refers to.
L242: change “in stead” to “instead”.
L274: The term ‘snow processes’ is still confusing to me. Why is ‘liquid precipitation’ in parentheses following ‘snow processes’ (again in L361). Are you referring to snowmelt and not rain?
L293/301: Please include the complete figure reference (i.e. Figure 5b & 5d instead of panel b and d). Further, please add more references to the figures when possible for justifying your statements. For instance, on L302 you write “Substantial influence of rooting depth on the evaporation simulation is visible”, but nothing is ‘visible’ if there is no reference to a figure or table for the reader.
L349: Why switch “increased” to “exacerbated”, they have opposite meanings here?
L382-384: Please specify whether the ‘differences’ or ‘changes’ are positive or negative when applicable here and throughout the manuscript.

Referee Report: PDF

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ED: Publish subject to minor revisions (review by editor) (16 Feb 2021) by Gabriele Messori

AR by Joost Buitink on behalf of the Authors (21 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (23 Feb 2021) by Gabriele Messori

AR by Joost Buitink on behalf of the Authors (03 Mar 2021) Manuscript

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Short summary

Higher temperatures influence both evaporation and snow processes. These two processes have a large effect on discharge but have distinct roles during different seasons. In this study, we study how higher temperatures affect the discharge via changed evaporation and snow dynamics. Higher temperatures lead to enhanced evaporation but increased melt from glaciers, overall lowering the discharge. During the snowmelt season, discharge was reduced further due to the earlier depletion of snow.