|The redrafted article is an improvement. The paragraphs explaining the differences between this contribution and others are direct and clear. Most other concerns were reasonably addressed as well.|
The idea of framing this as a methods/theory paper seems worthwhile, but the paper now seems cast as having two purposes rather than being fully repurposed. Explaining methods to explore potential differences versus making the argument that they represent a more fundamental truth about how groundwater is changing are different papers. Although the basic argument that groundwater warming follows from surface warming, and the more specific numerical analysis, is validated by the Menberg paper, the equations presented in this paper are not (although they are closely enough related that some credibility is offered). Would it be more appropriate that the authors acknowledge their own earlier work as having successfully made the argument that groundwater warming is important and present this paper as offering more easily generalized methods to evaluate groundwater temperature sensitivity?
At issue is the very common problem where physically based models, theories, or arguments are treated as reality. This is not to say that there is any problem with stating expectations based on physical arguments; that is how we build theory and ultimately hypotheses. But the best hypotheses are expressed for purposes of being tested, not being right. I admit that papers focusing primarily on new hypotheses with only a few data to support them are not always well received by reviewers in the field of hydrology, but such papers are more common in other fields. Perhaps since the argument has already been made in preceding papers that the phenomenon is important, it does not seem unreasonable to make space for offering some equations that could potentially be tested. This is probably all the more true since competing (subtly) theoretical/computational approaches have been recently proposed (Comola et al., in press at WRR) and it is a potential area of near-term scientific advance. A subtle change in tone of this paper would help, however.
There are a number of places where subtle shifts in wording and tone produce a remarkably different interpretation of (and possibly reception for?) the analyses the authors have done. For example:
P1 L32: “… are employed to investigate …” could be “… are employed to estimate …”
P2 L1 In “… formulae demonstrate that shallow groundwater will warm …” the words “demonstrate” and “will” seem overstated with respect to newly proposed formulae/models. Any number of more conditional phrasings would be more appropriate considering the lack of validation, including: ‘suggest’, ‘estimate’, ‘indicate’, ‘imply’, or ‘lead one to expect’, followed by ‘might’, ‘could’, or ‘should’, for example. These reframe the paper from being cast as an argument based on theoretical grounds with only a little empirical support to being a paper framing ways one could explore the issue or provide a testable hypothesis.
P28 L27- P29 L8: Technically, in this paper the authors have not “demonstrated” so much as “theorized”, or perhaps “extrapolated” or “interpolated” from previous studies. This paragraph is written as if the authors have found through testing of hypotheses and analysis of data that these are the facts of the case as opposed to their expectations based on reasoning. I won’t deny their argument is compelling or that their reasoning is sound, but the language used in drawing conclusions from process based reasoning is generally different from that used when data constrain the answer … particularly given alternative models to theirs exist – models that might not show as strong of an effect as theirs.
P2 L1: “Novel” is redundant with “are proposed”, and the word “novel” is ironically cliché in recent scientific papers.
Equation 17 slightly unclear because of wrapping of equation across lines– placement of second condition looks like it only applies to the second line.
P16 L10-15, could just be simplified to say, “Sensitivities for all times greater than T0 were calculated with respect to the initial temperature perturbation, DeltaT."
P24 L23-27: I agree with the general drift of this paragraph. Luce et al. (2014) did seem to let GW dominated systems off rather lightly in comparison to other effects that could not be modeled using interannual data. That being said, the statement/comparison the authors chose to use, the 23-year versus 100-year comparison for peat, is one of the more critical of their analysis … if put in terms of sand, it is less dramatic of a comparison, and the seasonal snowcover would ameliorate it all the more so. Perhaps the “very” in line 24 could be deleted and keep much of the same point without seeming quite so broadly critical.
P 25 L3-6: Arismendi et al did not test interannual models, they only tested intra-annual models. The distinction is important. It’s not a problem with regression, it is a problem with theory.
Comola, F., B. Schaefli, A. Rinaldo, and M. Lehning. "Thermodynamics in the hydrologic response: Travel time formulation and application to Alpine catchments." Water Resources Research (2015).