Dear dr Kirchner, dear James

Your paper is HESSD received detailed reviews for which I thank the reviewers a lot. Also, your prompt and detailed responses lead to ample time for lively discussion. The referees agree the presented approach is novel and of interest to the hydrology community. It is a creative, rigorous and timely contribution to the research on quantifying hydrological response in catchments and transit time in particular. It is very well written and presented, both the derivations and benchmark testing are presented and in my opinion the paper managed to facilitate readers to be able to reproduce the approach. Of course, for the latter, publication of the analysis code as supplement material would be useful.
Content-wise, only minor revision have been asked for, mainly additional explanation and discussion on results and limitation (like backward forward TTD, accounting for evaporation and discussion on long travel times and limitations). Already in the discussion replies have bene given and agreed to be included in the revision.
As remarked by the referees as well, the paper is unconventionally long. It combines - like said before - rigorous formal mathematical derivations and explanations with so now and then informal text. I can visualise this being presenting in an auditorium. This writing style is easy to follow and that is an achievement. The choice has been made to present almost all derivations in the main text in stead of referring to the original work only or to use more supplements/appendici. I agree that the elaboration on previously published work that is not often presented in the hydrological community is useful for many readers. I guess it is a matter of style if that better fits in the main text or as appendix/supplement. Ideally, I would like to see it in ‘explanation boxes’ as inset-boxes in the main text (an option not facilitated in HESS). But anyhow, I agree working with more supplements would not shorten the overall amount of text and could lead to some redundancy and cross-linking. I think the current solution by indicating which sections can be skipped or skimmed, is an acceptable form for this paper.

I look forward receiving the revised version in due time

Kind regards
Thom Bogaard

Dear James

It is a pleasure to inform you I decided to accept your resubmitted paper for publication. In my opinion all recommendations have been included and the revised submission also reflects the discussion in the open discussion phase.
I noted three small edits to follow up in typesetting phase. In my version I saw eq 3 was deleted but not replaced while it should be in. Second, equation 1-2 are the same as equations 4-5. I guess the paper and analysis is equally well to follow when eq 4-5 are deleted.
On page 31 line 22 it says: but in not the sampled rainfall. I guess it should read but not in the sampled rainfall.

I look forward to the follow up papers and scientific discussion your proposed methodology will definitively result in.

Kind regards
Thom Bogaard