Dear authors,

based on the feedback of the referees, your manuscript will need to undergo minor revisions prior to final publication. The paper has been judged as a very valuable contribution and of high interest for the readers of HESS. A few specific issues need to be dealt with:

- both referees have pinpointed that the discussion section (i.e. section 5) needs to be re-organised. Especially discussing your results with previous literature is of major relevance here (even though I understand that your study is specific in that it is the first tritium-based assessment of TT of baseflow carried out in a subtropical setting);

- some apparently counterintuitive results/outcomings of your study (e.g. increase in TTs of old water fractions after recharge events) need probably a few more developments - and discussion related to prior findings in literature (when possible).

It is also suggested to the authors to take into account as much as possible most technical recommendations of the referees in order to increase the readability of the manuscript (e.g. issues related to the large number of abbreviations used in the text).

As I understand from the comments made to the referees assessments, all issues can be addressed promptly - paving the way for a rapid processing of the manuscript past the minor revisions.

With best regards,

Laurent Pfister

Dear authors,

the revised version of your manuscript is significantly improved, as most recommendations of the referees have been considered. Therefore, I am happy to let you know that the manuscript can be accepted for publication. Before that, there are only a few small edits/corrections that would have to be carried out:

line 12: ‘older contribution TT’: as mentioned in the first review, this formulation is not clear, please rephrase.

line 20: ‘best fit’: specify between what these fits have been determined.

line 181: the reference to Groening et al. (2012) is missing from the reference list.

line 922. use ‘3H’ instead of ‘tritium’ for consistency with the other tables and the text.

Fig. 2. it would be good to vertically align the left y-axis of panel C to the ones of panels D, E and F, and the right y-axis of panels C and D to the one of panel E.

Fig. 4. it seems that in the main graph in panel A only a portion of the R1 samples are shown, as exemplified by the inset. However, this must be true, even if not specified, also for panel B because the x-axis scale goes up to -1.5‰ or so and thus trims away part of the R1 samples (that range up to -0.1‰, as shown in the inset of panel A and specified in line 277). This needs to be addressed.

Thank you for considering these technical corrections.

With best wishes,

Laurent Pfister