Field-scale water balance closure in seasonally frozen conditions

Pan, Xicai; Helgason, Warren; Ireson, Andrew; Wheater, Howard

doi:https://doi.org/10.5194/hess-21-5401-2017

Articles | Volume 21, issue 11

https://doi.org/10.5194/hess-21-5401-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-21-5401-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 21, issue 11

Research article

|

01 Nov 2017

Research article |

| 01 Nov 2017

Field-scale water balance closure in seasonally frozen conditions

Xicai Pan, Warren Helgason, Andrew Ireson, and Howard Wheater

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Final revised paper (published on 01 Nov 2017)
Preprint (discussion started on 16 Jun 2016)

Interactive discussion

Status: closed

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

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RC1: 'Review of Field Scale water balance closure in seasonally frozen conditions', Anonymous Referee #1, 07 Jul 2016
- AC1: 'Author response to Reviewer # 1', W.D. Helgason, 09 Sep 2016
RC2: 'Review of hess-2016-260', James Buttle, 13 Jul 2016
- AC2: 'Author response to Reviewer # 2', W.D. Helgason, 09 Sep 2016

Peer-review completion

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

ED: Reconsider after major revisions (09 Sep 2016) by Ross Woods

AR by Warren D. Helgason on behalf of the Authors (23 Feb 2017) Manuscript

ED: Referee Nomination & Report Request started (13 Mar 2017) by Ross Woods

RR by Anonymous Referee #1 (09 Apr 2017)

Suggestions for revision or reasons for rejection

In this revised manuscript the authors describe a study that confirms care must be taken when using residuals of the water budget to estimate hydrological fluxes. The authors have addressed several of the comments that were made by the reviewers. There remain a few outstanding problems that must be addressed before the paper could be accepted for publication.

First, the authors should explicitly state which water budget terms in Eqs. 1 -3 and 5 are measured and which are not. For instance, G, the net drifting snow is not measured. Nor are the individual components that comprise E. This might make the message about the importance of sound water balance measurements more complete. It is difficult to accept the argument of the authors that water balance uncertainty is very important when they did not attempt to measure all that could be measured. I agree with the authors that it is rare to attempt to measure all the major water budget components and our community needs to do a better job at this. Perhaps a better experimental design would have been to attempt to measure water budget terms in Eqs. 1-3 and 5 and then compare those with the 1D water budget equation.

Second, it seems more intuitive to have runoff the positive residual of the water balance. For runoff to occur there is some water left over from the 1D budget, some positive amount. Currently, the construct of Eqs. 1to 3 and 5 and the data in Table 1 all suggest that there is runoff when there is a negative residual. As a reader, I had a hard time conceptualizing the way the authors had built and used their water balance equations. Addressing the first suggestion may also help with this problem.

Third, while 2014 was wetter, the runoff response seems disproportionate to the increase in antecedent storage in the soil. Maybe the authors could provide information on porosity and specific yield in the site description. They could use this information to calculate what the storage deficits were in the top 1.6 m of soil. This could better explain the likely division of runoff and infiltration, and help the author’s argument.

Maybe the authors could end the article with a statement like; “robust field measurements of all presumed relevant water balance terms deemed important over the time scales of interest, or application”. It might be a good message to convey.

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RR by Anonymous Referee #3 (09 Apr 2017)

RR by Anonymous Referee #4 (05 May 2017)

Suggestions for revision or reasons for rejection

The paper by Pan et al. entitled “Field-scale water balance closure in seasonally frozen conditions” in essence measures the water balance in considerable detail for two water years in the Canadian prairies. It is a detailed water balance (really 1-D despite claims otherwise) of a pasture.

I have mixed feelings about this manuscript. First, it does present data that is of obvious high-quality, and the authors take some care in outlining the pros and cons of their measurements and assumptions, and the figures are for the most part clear and concise. On the other hand, the manuscript has some odd aspects to it that detract from its quality. It is hard for me to understand what is truly novel here, as the authors re-state issues that others have clearly identified before, but I can also understand that they have brought together a lot of good data and careful measurements to emphasize just how truly difficult it is to ‘close’ the water balance; clearly one of the most vexing things hydrologists have to do.

The authors lay out an introduction to water balances and the prairie region, yet I find the introduction is hampered by this entire issue of ‘naive assumptions’. I mean, come on, do these authors really think that hydrologists around the world do now know of the issues involved with measuring soil moisture, the pros/cons of energy balance closure, snow redistribution, gage under-catch, etc? I don’t think hydrologists are at all unaware of the pitfalls of measurement errors - and throughout the manuscript I would encourage them to remove this distracting language. Sentences like “As a result of the aforementioned complexities, prairie water balance is subject to spatial variability of precipitation inputs, water storage characteristics, and evaporation patterns” apply to virtually all environments. The hyperbole at the front should be tempered.

There is no objective in this paper. The sate that “we use a well-instrumented field site to quantify the magnitude of the water balance components as they vary across three distinct seasons in the prairies”, that they perform uncertainty analysis and assessed the validity of treating the problem as 1-D in different seasons. Okay, so why? What’s the science question here? What do the authors want to covey? What insights will hydrologists get. There is nice information here, but the introduction and setup are underwhelming.

The methods are set up clearly. I would encourage the authors to refrain from using bullets and that type of thing. The three seasons are identified, but the comment that in each period the water budget is different is obvious and doesn’t need to be stated. The authors have a nice site here with good instrumentation and careful measurements. The uncertainty analysis uses the classic sum of squares, but the authors mix ‘best guesses’ with more informed information on errors from sampling. I don’t want to get too critical here as this is always a difficult issue to evaluate, and it does help the manuscript, but there are are still errors that are not included. For example, as the authors are closing the energy balance to available energy (increasing fluxes >30%), then errors in radiation and ground heat flux have to come into play, etc., etc. I find that the error assessment was perhaps a big overstated in its importance, but this is not a major issue.

The results are laid out in a systematic manner accompanied by nice figures. The three seasons are laid out and the errors, uncertainties and major processes described. A few things I’m curious about - the deeper freezing in 2014 with wetter soils doesn’t make a lot of sense to me as drier soils (with less latent heat to overcome) typically freeze deeper all things being equal. However, none of these soils are that wet. The change in moisture content over winter is also quite interesting. The upward movement of water to freezing fronts are invoked, but I wonder if this is possible (ie the necessary suctions and the rates). Some back-of-the-envelope calculations and/or some modeling could answer this but I assume the authors want to keep this paper based on observation. The explanation of runoff processes based on SWE and the gage data ignores issues on the prairie landscape such as detention storage, fill-spill mechanisms, etc., that have been talked about in great detail over the past few decades.

The manuscript ends with some advice for others who are concerned with water balances in strongly seasonal and cold environments. This has all been stated before and I suppose it is good to reinforce these points, but the authoritative language and the statements about naive water balances left me unimpressed at the end.

I did not read the other reviewer comments until I had read and reviewed this manuscript (I am not a fan of how HESS has reviews open for others to see as I often find it pre-biases people). That said, I can see how the authors have attempted in some ways to revise the manuscript, but as my concerns are fairly in line with what the other reviewers have suggested, I’m not sure that the authors have done enough. That said, I loathe to see good data like this not be published as it is valuable. I suggest that the authors reframe the manuscript to identify critical science questions or hypotheses and use data to answer those. For example, questions regarding the influence of over-winter moisture redistribution, the role of field scale variability (not addressed that well in all honesty despite presented data), links between not just SWE but other melt/soil conditions on runoff, etc., would all help make this more engaging to the reader and highlight the scientific importance of the work. At the moment, it simply reiterates past knowledge and reminds us of experimental pitfalls.

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ED: Publish subject to revisions (further review by Editor and Referees) (30 May 2017) by Ross Woods

AR by Warren D. Helgason on behalf of the Authors (12 Jul 2017) Author's response Manuscript

ED: Publish subject to minor revisions (further review by Editor) (20 Jul 2017) by Ross Woods

AR by Warren D. Helgason on behalf of the Authors (25 Jul 2017) Author's response Manuscript

ED: Publish as is (25 Jul 2017) by Ross Woods

AR by Warren D. Helgason on behalf of the Authors (04 Aug 2017)

Short summary

In this paper we present a case study from a heterogeneous pasture site in the Canadian prairies, where we have quantified the various components of the water balance on the field scale, and critically examine some of the simplifying assumptions which are often invoked when applying water budget approaches in applied hydrology. We highlight challenges caused by lateral fluxes of blowing snow and ambiguous partitioning of snow melt water into runoff and infiltration.