Dear authors,

Thank you for your detailed replies to the the comments of the 2 reviewers. As you have acknowledged, both reviewers raised a couple of interesting points, a few of which are of considerable importance for the underlying interpretation of your results. I very much appreciate that you invested some time to addressed most comments in-depths. Yet, I feel that some points need a bit more attention in order to clarify your approach for the reader and to avoid misinterpretations:

(1) relating to comments of both reviewers, it remains unclear *how* pQ is constructed in your study. More specifically: which pQ does the reader actually get to see? Is it the age distribution of an incoming signal J that leaves a grid cell through *all* exit routes (i.e. Q and ET)? or is it only the age distribution of water leaving the unsaturated zone (Q and ET?) as I seem to understand from your reply No.8 to reviewer 2? In case groundwater storage was considered, how was the hydrologically passive storage accounted for (see e.g. the well known Fogure 1 in Zuber, 1986, Journal of Hydrology 86) - this is highly relevant for the age distributions as it exacerbates the dichotomy between celerity and velocity (McDonnell and Beven, 2014)! In addition, as you showed, mhM uses several soil layers. Is pQ a direct reflection of the total outflow from *all* soil layers? A further point is that only 5 years of warm up period were used. As the subsequently used "mean" age can be considerably sensitive to long tails, what is the potential of your estimates being biased towards too young water? In other words, even with 50 years modelling, is it conceivable that we miss some minor volumes of very old water here? These points need to be made much clearer - in the methods but also in results&discussion sections (particularily in the figures!).

(2) Not everybody may be familiar with the details of mhM and of how the parameters are obtained in that model. It may therefore be important to clarify much earlier in the manuscript, how the soil moisture storage capacity is determined. Attentive readers will otherwise wonder if some of the storage is unaccounted for if the value is a "normal" calibration parameter (i.e. potential "passive" storage" that within you period of application does not become hydrologically active but may provide a mixing volume; see above and McDonnell and Beven, 2014).

(3) I am missing a clear research question and/or research hypothesis this manuscript is looking at. Please add that at the end of the introduction.

(4) Note that figure cpations should be stand-alone. In other words, the reader should be able to understand the figure by reading the captions alone. At the present the captions a very vague and uninformative. I would encourage you to be more specific and detailed. Only one example: what are the soil classes 9, 38, etc. in figure 14. what type of soils are we talking about?

In general, I would be glad if you could invest some more time in developing a more detailed and clear description of your methods and a stronger discussion of the limitations of the chosen approach (e.g. what about parameter uncertainty? uncertainty in age distributions? etc. and the effect on the interpretation)

I will be glad to receive a revised version of the manuscript, which will then be sent out to a second round of reviews.

Best regards,

Markus Hrachowitz

Dear authors,

thank you very much for addressing in detail the reviewer comments. Before I can accept the paper for publication, I would like to encourage the authors to have the manuscript checked by a native speaker due to a considerable number of spelling errors. In places the grammar also does not seem to be fully correct and some of the wording comes across as a bit awkward.
In addition, please make sure to format the figures in an appropriate and complete way so that all axis are not only given symbols but also the associated units. the same is true for the legends (i.e. colour codes): although it is mentioned in the figure captions, make sure to provide units.
Best regards, Markus Hrachowitz

Dear authors,
thanks for taking my additional comments into consideration. i think, the manuscript is now developed to the point that it is a very interesting contribution to literature and i am pleased to accept it for publication as is. congratulations!
best regards, markus hrachowitz