|ROUND #2 REPORT MAGNIN ET AL. 2016|
This round #2 report is composed of two sections. In Section A I look at round #1 reviews and attempt to assess if the authors have addressed reviewer concerns satisfactorily while keeping an open and critical mind to those concerns. In Section B I detail some of my own comments.
SECTION A: AUTHORS RESPONSE TO REVIEWERS
I distill the main concerns as the following:
1. Not significant progress in permafrost modelling
While I take the reviewers point of lack of methodological developments in the paper I do think there is value in presenting site-specific studies of permafrost evolution in this significant part of the European Alps. In addition, the authors have in-situ data to draw on both in terms of model boundary conditions and evaluation. Realistic site-specific pathways of permafrost evolution according to latest RCP's has, to my knowledge, not been presented in this region, and therefore I would argue of interest to the community, despite usual caveats of the simple modelling approach. The authors use existing methods and data to derive new results, given the title of the special issue that this manuscript was submitted to I would say it is an appropriate and useful contribution.
The additional charge of the result being 'unsurprising' is, in my mind, not entirely fair and could be levelled at most climate change studies. Given warming scenarios, we expect permafrost degradation, of course. But what I think this study does nicely is show probable spatial and temporal patterns of change for three specific sites with enough good data in two to perform a reasonable evaluation based on attempting to reproduce current conditions.
2. Does not address stability assessment
Firstly I would say that stability assessment is not a stated aim of the paper, even if it is a motivation. I would then argue that getting the thermal field right is a first and important step in a stability assessment of permafrost slopes. The geomechanics, hydrology etc. are important but separate processes likely requiring different modelling approaches and beyond the scope of this study.
The newly added Section 5.3 seems to be a reasonable response to the raised concerns whereby the authors describe contributing factors to rock wall stability processes and describe the types of model that would be required to simulate these processes. I think in terms of the current state of the art, this is clearly a separate problem with these research topics still relatively new and therefore beyond the scope of this paper. However, as the authors state, future integration of thermal, hydraulic and mechanical processes will be key in providing an accurate simulation of rock wall destabilisation.
3. No consideration of precipitation changes
While the hydraulic effects of changed precip regimes may certainly play a role in rock wall stability, it is the thermal effect of a changed average snowpack depth that is of primary importance in permafrost degradation and permafrost studies on climatic change timescales - however, this effect is generally marginal in the situation of steep rock walls. In addition, as the authors mention, uncertainties in precipitation scenarios are usually high, especially with respect to site-specific studies. I am therefore satisfied with the additions the authors have made to the introduction and discussion.
SECTION B: OWN COMMENTS
1. p2 l4: what is 'this warning study' you mention?
2. p2: reference to Blunden and Arnt is disingenuous as that publication refers to north slope boreholes whereas you are discussing steep rock boreholes in the Alps where to my knowledge trends are less clear (partly due to generally short measurement periods)
p.20l6-7: you state that summer precip will 'certainly decrease' in the Alps. The given citation describes the study of Rajczak et al 2013 which shows that “that the frequency of wet days (left column) is projected to substantially decrease in summer across the entire Alpine region”. I think you should rephrase your statement more carefully as there is never certainty in model results. Perhaps: “Climate studies have shown a high likelihood that summer precipitation will decrease in the European Alps.”
3. As mentioned by previous reviewers, I still find grammar not quite up to scratch in numerous places and would recommend a second proof-read prior to publication.
4. I am confused by the author's continued use of the word debatable, eg:
“short time scale changes are debatable but beyond the scope of this study”
5. I found it hard to trace the various comments/responses, I would suggest, in future, that the authors organise their responses clearly by each referee report in order to make this task easier.
In conclusion, I support the publication of this revised manuscript in the context of the special issue, subject to minor/technical comments listed above.