Dear Authors,

Two reviewers thoroughly evaluated your manuscript. Main points were raised that concern (i) the presentation of spatial resolution in the Figures (topography and isotopes), (ii) explanation of differences in d-Excess, (iii) comparison isotope contents of one time surface water samples with spatial and temporal patchy isotopes in precipitation, and (iv) missing information about data collection.

You answered in detailed to all the reviewers’ comments. I agree to almost all answers and additionally have some important points I want to emphasize:

1) Concerning the explanation of differences in d-Excess, I highly recommend including the evaporation into the discussion of the manuscript, because it seems to be important when comparing the reported ranges of d-Excess in precipitation and surface water. Not only seasonal recharge can result in lower d-Excess, but also evaporation. Even if the data plot close to the GMWL, it is no evidence for lack of evaporation as (i) LWMLs would be required and (ii) mixing of surface water from different regions would even require more detailed knowledge about the regional distribution of isotopes in precipitation, both in time and space. Besides, the authors refer to Figure 2 in their answers concluding that evaporation is not of major relevance. However, the line already inherits evaporation effects and -as correctly mentioned in chapter 3.2- is different compared to the Japanese Meteoric Water Line. Summarizing, evaporation needs to be included in the discussion more critically.

2) Further, I agree with one of the reviewers pointing out the complex relationship between precipitation and surface water. I already asked for more details here when the manuscript was submitted the very first time (“One main issue concerns the length of the sampling period and whether it biases the isotope results. Certainly, such a high number of samples cannot be taken in just some weeks. However, if there still is a seasonal signal of isotopes in stream water, you cannot compare samples that were taken 3 months apart. Then the isotope content in stream water strongly depends on the travel time of the river water and you do not have a temporal integrated isotope signal of precipitation reflected in a one-time sampling time in stream water as indicated on page 8 ln 4-5. I suggest two things: first, convince the reader that the samples are not biased depending on the date they were taken and second, at least discuss the possibility of different water transit times and recharge areas in your catchments.”). In your answer it is indicated that samples were taken during base flow conditions and that the base flow is mainly groundwater. You also mentioned that it is shallow groundwater. Here, the seasonal signal of isotopes in precipitation can still be present if transit times are short. Please take this point into consideration when revising the manuscript.

Due to the many comments requiring detailed rewriting of the manuscript, I will reconsider the manuscript after major revisions have been done.

I am looking forward reading your revised manuscript
Christine Stumpp

Dear Authors,

Thank you for following the reviewer’s suggestions and revising the manuscript accordingly. Both reviewers were pleased to see the improvement of your manuscript. In particular, it was highly appreciated that the raw data were provided in an annex. Still, some very minor points were raised which you find attached in the reports and which I summarize quickly also including my own comments:

1) The discussion of evaporation was improved; however, some important points are still not discussed explaining the very low slopes (Table 2) of the linear regressions. What is the reason for these low slopes which sometimes are even lower compared to theoretical evaporation lines? Is there any influence of hot springs and geothermal water; particularly in the Chugoku and Kinki regions? In addition, is there any influence on dual moisture sources with the regions?

2) The section on comparison with other isoscape models requires some rewording. One reviewer certainly agrees that globally adjusted models have limitations. Still, they are useful for predictions in areas with scarce data. How can your study improve gaps associated with little information on isotopes in precipitation?

3) Figure 4: One reviewer suggested changing the color codes, i.e. depleted values blue and enriched values red. The other reviewer was missing the contour lines. Going back to the first round of reviews, it was already suggested to include GIS based small-scale contour plots. If you are not familiar with generating these contour plots and cannot provide isoscapes in an appropriate spatial resolution, please at least change the color code of the gridded data.

4) Please check the grammar carefully again and change some terms regarding isotope terminology (use lower or depleted instead of smaller).

I am sure these minor points can be addressed easily and I am looking forward receiving your revised manuscript

Christine Stumpp

Dear Authors,

Thank you for improving the manuscript based on the reviewers' helpful comments. It is a pleasure to accept your paper for publication. Thank you for submitting your manuscript to HESS.

Regards
Christine