This manuscript wishes to deliver a standardization approach of how to measure fractures in the field, with application to Earth surface related researches. I appreciate this effort to define a standardization or at least a guidance (I am not that convinced by the need for standardization - see my first main comment) on how fracture measurement should be performed. This can be extremely valuable as a starter guide for young or more experience researchers or students who need to measure fractures in the field. Most of the advices seem justified, and the guidance is quite thorough and exhaustive. I congratulate the authors for that, and I am convinced this will be useful to the community. However, in its current form I have some strong doubts about the publication of this manuscript in Esurf, as it is a paper that develops a standardization approach without bringing new results. My recommendation to the Editor is therefore to suggest the authors to consider another, more technical/methodological outlet  (see my last main comment).

Here are my main criticisms:

• Standardization or Guidelines - In my opinion, the paper should read more as a series of guidelines or good practices than really the standardization of an approach. The phase of standardization generally occurs after there has already been extensive research in a particular field so that 1) it is quite clear what are the best practices, and 2) there is a clear need to make datasets comparable, in particular for applied sciences. In geomorphology, studying fractures related to geomorphology is almost exclusively limited to fundamental research, and the topic remains a niche topic investigated by only a few researchers or groups worldwide. This is also highlighted by the large number of self-citations (13) of the main author in this manuscript. Please do not get me wrong, I am not here criticizing these self-citations, which are indeed pertinent ones, but I believe this shows that the study of fractures in geomorphology still remains a niche topic (despite being a very interesting and promising one). I also believe a more community-wide approach to standardization is required to prevent secondary effects, such as studies rejected because of a lack of consistency (despite being sound) with the methodology described here. So, at this stage, providing guidelines is useful, but defining a standardization might be unnecessary or too early.
• Accounting for automated measurements - I also feel that in terms of timing, it might be too late (sorry for the apparent contradiction with previous sentence) to define a standardization approach simply based on manual measurements in the field. There are now plenty of – and at least a few good - algorithms and softwares that can help to automatically identify, and measure fractures or sediment grains based on 2D images or 3D point clouds at all scales. These methods are more and more routinely used by research teams and are generally successful to limit or remove operator bias and to lead to reproducible measurements. I agree that they cannot be used in all conditions and that hand manual measurements remain a complementary and more polyvalent approach, as it brings confidence to the automatic approaches. But I also believe that the need for standardization has clearly changed since the last century (when most standardization approaches were defined in Earth sciences). The manuscript ignores or does not account for these more automated and more objective approaches, while they will probably represent a universal approach to fracture analysis in the following years or decades.
• A too long paper - The paper is well written, but it is also too long with too many details, and it is sometimes hard to follow the logic of its organization. The authors therefore need to make a clear effort to explain these guidelines in a more synthetic way, and even more importantly to motivate the readers to read it and to better justify why these guidelines are important (section 1 does not fully succeed to do that). This is critical. Indeed, if the authors wish the general audience to follow these guidelines, they need to make sure that most researchers - interested in fractures for Earth surface related research – read thoroughly the paper. And I have strong doubts this will be the case with the present form of the manuscript.
• Arbitrary choices while developing a standardization approach - Some choice of how to measure fractures are not sufficiently justified. As an example (but there are several other examples), it is mentioned in section 5.4.1 that “If a seemingly continuous crack (Fig. 2b, left) is in fact separated by bridges of solid rock (Fig. 2b, right inset), then these should be measured as two different cracks and their lengths should terminate at the rock bridges”. This statement (as some others) is not - or not sufficiently - justified or motivated. For instance, in this case, can’t there be some long fractures with some small rock bridges (which are quite common due to fracture roughness) that mechanically behaves as long fractures and not as a series of smaller fractures? Then why and on which scientific basis should we separate the fracture in smaller segments? This is problematic as it gives an impression of arbitrary choices, while defining a standardization approach that can be useful only if there is a community agreement, obtained after a logical explanation, about these apriori best practices.
• Hierarchy of State Factors - The presentation of the State Factors is interesting, but probably lacks a bit of hierarchy. Currently, all the State Factors as cl,o,r,p,t,T (climate, organisms, relief, parent material, time and Tectonics) are presented at the same level without a clear hierarchy, as if each of these factors had the same weight in controlling fracture growth, which is likely not the case. I agree that considering subcritical growth – which is something important and often neglected - brings some complexity. But it also leads to some confusion about the role of each of these factors. Some factors mainly lead to a global – almost static on human timescale - stress field (tectonics and relief), some induce some local temporal stress variations (e.g., pore pressure – related to hydrogeology and climate / thermal expansion – related to heat and insolation), and some lead to favorable conditions for subcritical crack growth (e.g., time, water chemistry, organisms). I suggest presenting these State Factors with a more explicit hierarchy and more explicit link to either critical or subcritical growth.
• I must finish by stating that I am not used to review a manuscript dedicated to developing a standardization approach, so my evaluation might not be relevant. Yet, I also question the suitability of Esurf for publishing a manuscript (that clearly deserves to be published somewhere, as mentioned earlier these guidelines are useful) that is technical and does not really bring new results (section 8 presenting a case example is not really a thorough demonstration of the need for standardization). Esurf is supposed to publish either Research articles (which report substantial and original scientific results within the journal scope) or Review articles (which summarize the status of knowledge and outline future directions of research within the journal scope) or Short communications. The editorial team will have better assessment than mine, but my opinion is that this manuscript does not correspond to any of these article types.

Last, I note that I have not checked in details potential syntax issues or less minor issues than the one mentioned, as I believe we first need to clarify these more important comments that I have mentioned above.

Dear authors,

The submitted manuscript provides a very useful summary and synthesis of good practices for the quantification of fracture networks for the purpose of surface process studies. 

It is useful for this community but not only, and thus I recommend the acceptance after minor revision.

Where I have the most trouble with is the mixed use of the terms cracks/fracture, which is for me more confusing than picking one over the other. As the title of the article refers to fracture, I would suggest using this term only throughout the manuscript and mentioning the reasons for this choice in the introduction.

Moreover, the language and writing style could be revised in some sections with a more nuanced and neutral tone and a bit less of a "we" form.

Some paragraphs also need to be rephrased and revised accordingly but don´t understand me in a bad way, the overall quality is really good.

I attached here the annotated manuscript with specific comments.

Congratulations again to the authors, I hope to see this work published soon.

Best regards,

Dr. Claire Bossennec