The role of vadose zone physics in the ecohydrological response of a Tibetan meadow to freeze–thaw cycles

Yu, Lianyu; Fatichi, Simone; Zeng, Yijian; Su, Zhongbo

doi:https://doi.org/10.5194/tc-14-4653-2020

Articles | Volume 14, issue 12

https://doi.org/10.5194/tc-14-4653-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/tc-14-4653-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 14, issue 12

Research article

|

21 Dec 2020

Research article |

| 21 Dec 2020

The role of vadose zone physics in the ecohydrological response of a Tibetan meadow to freeze–thaw cycles

Lianyu Yu, Simone Fatichi, Yijian Zeng, and Zhongbo Su

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Final revised paper (published on 21 Dec 2020)
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Preprint (discussion started on 12 May 2020)
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Interactive discussion

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

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RC1: 'How vadose zone mass and energy transfer physics affects the ecohydrological dynamics of a Tibetan meadow? by Lianyu Yu et al.', Anonymous Referee #1, 17 Jun 2020
- AC1: 'Reply to Reviewer 1', Lianyu Yu, 31 Jul 2020
RC2: 'Review of 'How vadose zone mass and energy transfer physics affects the ecohydrological dynamics of a Tibetan meadow?'', Anonymous Referee #2, 22 Jun 2020
- AC2: 'Reply to Reviewer 2', Lianyu Yu, 31 Jul 2020

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (14 Aug 2020) by Ylva Sjöberg

AR by Lianyu Yu on behalf of the Authors (02 Sep 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (17 Sep 2020) by Ylva Sjöberg

RR by Anonymous Referee #1 (29 Sep 2020)

Suggestions for revision or reasons for rejection

On the role of vadose zone physics in the ecohydrological response of a Tibetan meadow to freeze-thaw cycles, Lianyu Yu et al.

The revised version of the manuscript has improved substantially, and I would like to thank the authors for their efforts to address my comments. The description of the three model versions is much more understandable and it is now made very clear what the differences between the three model versions are. I also appreciate the additional figures in the supplementary material that help to evaluate the three model versions separately.
I have two major comments left (one regarding the manuscript itself, and one regarding the measurement data used), and have a number of smaller remarks that may help to improve the manuscript. Once these are taken into account, I consider the manuscript acceptable for publication.

Major remarks:

In the introduction, relevant studies are mentioned as examples of modelling studies on relevant ecosystems, but merely as a list of examples without reference to their outcomes. They are listed to have shortcomings because processes are “independent and not fully coupled” – it would be great to have this argument explained further based on the referenced studies, because the manuscript addresses exactly these shortcomings.
It is not clear to me whether the observed turbulent fluxes in Fig. 4 were determined from the eddy covariance system (L. 115) or from energy balance computations – the manuscript mentions only the eddy covariance system, but there is a striking similarity in the time series of Rn and LE (Fig. 4a and 4c), hinting at the possibility that LE is computed based on Rn instead. If these data are based on eddy covariance, please explain how processing and gap filling was done (similar to the description of the carbon fluxes, section 2.2.1), and whether the measured Rn is used in any way for this.

Minor remarks:

- L. 12: “… even more so in cold regions…”: It is not clear to me why vadose zone would be more crucial in cold regions than in others – there are many other ecosystem types where the vadose zone can also be attributed a crucial role for ecosystem processes (e.g. in subtropical arid and semi-arid ecosystems).
- L. 17/L. 80/L. 267: Abstract and manuscript discuss in several places “the ice effect” or “soil ice effect”. Please clarify briefly which effect of ice is referred to when using the term, it is not always clear from the context that this refers to the impact of freezing-thawing on energy and water properties.
- L. 38: replace “ecosystem” with “an ecosystem”.
- L. 82: Replace “does” with “do”
- L. 87: “process” is not clear here – maybe “detailed soil mass and energy transfer scheme”?
- L. 90: replace “facilitating” with “facilitate”
- L. 167: remove “however”
- L. 279: Is any information on longwave radiation going into the model, or is it only used for evaluation?
- L. 282: “second values”: Does this refer to values every second, or simply any value between the two hourly values that you have data for? Please clarify.
- L. 357: Check spelling of “cryosuction”
- L. 422: I would not refer to these as “model scenarios” but “model versions”

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RR by Pierrick Lamontagne-Hallé (04 Oct 2020)

Suggestions for revision or reasons for rejection

I would like to thank the authors for fully addressing my concerns with their responses and for applying the requested changes in their manuscript. I feel that the manuscript has greatly improved from the open discussion review process and, as a result, I think it is now suitable for publication and would be very relevant to The Cryosphere. I would also like to congratulate the authors for a well-structured study that I find personally very interesting. Below are a few more minor comments and suggestions.

Title: I do not think the “On” in the title is necessary.
Line 58: MarsFlo became the Advanced Terrestrial Simulator a few years ago and now incorporates way more processes than it used to. I suggest the authors to use a more up-to-date reference such as Painter et al. (2016). Other good recent examples also include the numerous cryohydrogeologic numerical models presented in Grenier et al. (2018) and Lamontagne-Hallé et al. (2020).
Line 79: This is a personal preference, but I would argue that almost all modelers consider their models to be “state-of-the-art”. Considering this, I think these words rather qualify the opinion that the authors have towards their own modelling tool and are therefore unnecessary.
Lines 94-100: I do not understand why the authors move this paragraph to this section, but I think it belongs more to the introduction. They could also consider deleting it if the authors wish to reduce the length of the manuscript as I do not feel it adds any useful information.
Line 122: The authors talk about “A few dedicated SMST profiles”, although it seems like only one profile has been used to compare to the modelling results. Can the authors either precise which profile has been used (on Figure 1) or how many profiles have been used?
Lines 126-131: According to me, this paragraph belongs in the section 2.2.
Line 189-190: “the thermal effect on water flow” is rather imprecise. One could see the temperature-dependence of hydraulic conductivity as a thermal effect on a water flow, which is consider in T&C-FT. Do the authors simply mean the thermal effect on water viscosity?
Lines 206-207: Unnecessary parenthesis after e.g.
Line 307: “because the true winter precipitation is difficult to observe” is repetitive with “can be partly attributed to the uncertainties of observed winter precipitation events” written earlier in the same sentence.
Line 317: “Figure S2-3” Do the authors mean Figure S2 and Figure S3? If yes, I think this should be written “S2 and S3”.
Line 417: This sentence does not make sense to me. I recommend the authors to read it again and make sure there are no words missing.
Section 5: I think this should be a sub-section of section 4 as this should be part of the discussion.
Lines 461-463: I respectfully disagree with this sentence. I highly doubt the importance of heat advection is limited to the frozen period. Kane et al. (2001), for example, states that heat advection can be quite important during freshet due to increased infiltration from snowmelt. Other studies in permafrost environments had similar conclusions (Chen et al., 2020; Sjöberg et al., 2016).
Line 467-469: I am surprised by this sentence. I agree that latent heat will slow down the freezing or thawing process, but I do not think the same can be said about heat advection. Heat advection has been shown to increase thawing rate in permafrost environments (Dagenais et al., 2020; Devoie et al., 2019). I recommend verifying this statement and specify how Figure 6 precisely demonstrates it.
Table 1: I think including such a table is very useful. However, I think it would be easier to read if the more information was included in the table itself instead of the underlying note. For example, it seems like the table is large enough to include “Latent heat” and “Convective heat” instead of “LH” and “CH”. I would also simply add “on soil properties” next to “ice effect”.
Figure 1: I do not think this figure adds any useful information. The second image is particularly painful to read as labels are stacked on top of each other and the legend is very small. If the authors decide to keep this figure, I strongly recommend improving its formatting as it currently looks like a quick snapshot from ArcMap. For example, I do not think the labels are necessary as these are never discussed in the text.
Figure 2b: I think this graph looks too complicated for what it represents. Instead of referring to thawing and freezing fronts, why not simply make this graph look like a cross-section (with the same x-axis as date) where frozen and unfrozen layers are clearly represented by different colors? That would probably be easier to interpret for the readers. See sketch attached to this review for a very quickly drawn example. Furthermore, it is very unclear what the black line represents (FTFP).
Figure 7: I don't fully understand the choice of the temperature scale here. Why going from 50 to -25°C while the temperature data seems to be within 25 and -20°C? It makes it harder to see the differences between the different simulations.
Figure 8: I think the direction of the water flux should be specified (e.g., positive = upward flow).

References
Chen, L., Fortier, D., McKenzie, J. M., & Sliger, M. (2020). Impact of heat advection on the thermal regime of roads built on permafrost. Hydrological Processes, 34(7), 1647‑1664. https://doi.org/10.1002/hyp.13688
Dagenais, S., Molson, J., Lemieux, J.-M., Fortier, R., & Therrien, R. (2020). Coupled cryo-hydrogeological modelling of permafrost dynamics near Umiujaq (Nunavik, Canada). Hydrogeology Journal. https://doi.org/10.1007/s10040-020-02111-3
Devoie, É. G., Craig, J. R., Connon, R. F., & Quinton, W. L. (2019). Taliks : A Tipping Point in Discontinuous Permafrost Degradation in Peatlands. Water Resources Research, 55(11), 9838‑9857. https://doi.org/10.1029/2018WR024488
Grenier, C., Anbergen, H., Bense, V., Chanzy, Q., Coon, E., Collier, N., Costard, F., Ferry, M., Frampton, A., Frederick, J., Gonçalvès, J., Holmén, J., Jost, A., Kokh, S., Kurylyk, B., McKenzie, J., Molson, J., Mouche, E., Orgogozo, L., … Voss, C. (2018). Groundwater flow and heat transport for systems undergoing freeze-thaw : Intercomparison of numerical simulators for 2D test cases. Advances in Water Resources, 114, 196‑218. https://doi.org/10.1016/j.advwatres.2018.02.001
Kane, D. L., Hinkel, K. M., Goering, D. J., Hinzman, L. D., & Outcalt, S. I. (2001). Non-conductive heat transfer associated with frozen soils. Global and Planetary Change, 29(3), 275‑292. https://doi.org/10.1016/S0921-8181(01)00095-9
Lamontagne‐Hallé, P., McKenzie, J. M., Kurylyk, B. L., Molson, J., & Lyon, L. N. (2020). Guidelines for cold-regions groundwater numerical modeling. WIREs Water, e1467. https://doi.org/10.1002/wat2.1467
Painter, S. L., Coon, E. T., Atchley, A. L., Berndt, M., Garimella, R., Moulton, J. D., Svyatskiy, D., & Wilson, C. J. (2016). Integrated surface/subsurface permafrost thermal hydrology : Model formulation and proof-of-concept simulations. Water Resources Research, 52(8), 6062‑6077. https://doi.org/10.1002/2015WR018427
Sjöberg, Y., Coon, E., K. Sannel, A. B., Pannetier, R., Harp, D., Frampton, A., Painter, S. L., & Lyon, S. W. (2016). Thermal effects of groundwater flow through subarctic fens : A case study based on field observations and numerical modeling. Water Resources Research, 52(3), 1591‑1606. https://doi.org/10.1002/2015WR017571

Referee Report: PDF

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ED: Publish subject to minor revisions (review by editor) (16 Oct 2020) by Ylva Sjöberg

AR by Lianyu Yu on behalf of the Authors (26 Oct 2020)

ED: Publish subject to technical corrections (11 Nov 2020) by Ylva Sjöberg

AR by Lianyu Yu on behalf of the Authors (16 Nov 2020) Author's response Manuscript

Short summary

The role of soil water and heat transfer physics in portraying the function of a cold region ecosystem was investigated. We found that explicitly considering the frozen soil physics and coupled water and heat transfer is important in mimicking soil hydrothermal dynamics. The presence of soil ice can alter the vegetation leaf onset date and deep leakage. Different complexity in representing vadose zone physics does not considerably affect interannual energy, water, and carbon fluxes.