Editor decision after discussion phase:
Dear Julia Eis and co-authors,
Your manuscript received 2 detailed but critical reviews that both highlighted the importance of the general topic of initialization and model uncertainty estimation in the glacier flow modelling community and that emphasized the good quality in presentation and writing. Further the manuscripts seems within the scope of TC.
However, besides some minor editing corrections the referees both consistently raised some more major issues/weaknesses that I briefly list below:
1) the manuscript seems perhaps to have and overly theoretical focus and the related link/relevance to real world observations is somewhat missing and thereby the relevance/benefit for the wider glacier modelling community not clear enough.
2) related to the above, the aim and main objective/value is not clear enough and needs better justification.
3) the link/relation to the well known response time should be better integrated.

Thus, the manuscript requires major revisions regarding the points above. Given your response as authors it seems that you already undertook such substantial revisions and that you seem to address these major points to a large degree, e.g.
-clarify and justify why you stick to a theoretical/sythetical study and why you do not compare to real world observations,
-better explain/show the relevance of such a synthetic modelling study and clarify the objective of the study.
-Youy also seem to integrate better the concept of response time and address the more minor points by the referees.
Thus, from the information I have so far, it seems, that a revised manuscript (as indicated in the response) should have the potential to be accepted. However, as the asked revisions were rather major, the paper will likely be sent for review again.
Please address all the raised points by the referees point by point in the revised manuscript.
I would like to thank the authors for their careful treatment and addressing of the referee comment in their response and look forward on the revised version of the manuscript.

Andreas Vieli, editor
15 Sept 2019

Dear Julia Eis and co-authors,
Your manuscript received 2 detailed but critical reviews that both highlighted the importance of the general topic of initialization and model uncertainty estimation in the context of glacier flow modelling community and that emphasized the good quality in presentation and writing.

The revised manuscript has now addressed all the major points raised by the referees, more specifically:
- the motivation and justification of the theoretical focus is now clear and the relevance has been clarified,
- the general aims and objectives have been adjusted,
- the concept of 'response time' has been integrated
- and the minor editingcissues have been corrected.

This has been confirmed by an external review by one of the previous referees (see below). Thus, I am happy to announce that the revised manuscript can now be accepted under the condition of addressing the few very minor issues spotted in the re-view as listed below.

I congratulate the authors for their very interesting paper and also would like to thank them for their thorough revisions and excellent handling of the revision process.
Best regards
The editor, Andreas Vieli, 17 Nov 2019

List of corrections:
-P1L24-25: Remove '[...] since it is the only data available for almost all glaciers globally'. The sub-clause confused me.
-P3L9: 'perfectly correct' --> 'perfect'
-P3L9-10: Reformulate. Suggestion: 'Specific research questions are:'
-P10L30: Invoke response times in this passage.
-Please also acknowledge the two anonymous referees in the acknowledgments.

Referee comments of revised version:
I appreciate the effort the authors have undertaken to revise their manuscript. It strongly gained in clarity and the presentation is now much more concise. The authors took the raised comments serious and expanded/adjusted the manuscript accordingly. I also want to emphasise the high quality and suitability of all figures, which quicklly guide the reader to the important aspects. This will make the article attractive for reading by a broad audience.
I therefore want to congratulate the authors to this excellent piece of scientific output.
I only have a few last minor comments.
List of corrections:
P1L24-25: Remove '[...] since it is the only data available for almost all glaciers globally'. The sub-clause confused me.
P3L9: 'perfectly correct' --> 'perfect'
P3L9-10: Reformulate. Suggestion: 'Specific research questions are:'
P10L30: Invoke response times in this passage.