Dear Prof. Koutsoyiannis,

I had a close look at your manuscript, the reviewer comments of Prof. Kundzewicz, Dr. Kleidon and your very detailed response to their comments. I agree with both reviewers, that your manuscript is very rich in content. One key point is surely the presented analysis of how atmospheric state variables have been developing up to the present that is based on globally available re-analysis data sets, which particularly reveals that relative humidity is by no means invariant, but has even declined in certain altitudes. This finding is of high interest as it speaks again a wide spread assumption underlying model based climate change projections. I dare say that I also found your response to Dr. Kleidon’s comment on Figure 7 of your manuscript quite convincing. Moreover, as none of the reviewers has criticized the soundness of the presented analysis, I overall conclude that the proposed work is definitely worth to be published in HESS and I personally think it is of high significance.

Yet I think the manuscript needs to be optimized to help the reader to better make her/his way through your study, which covers a considerable amount interesting topics, as pointed out by Prof. Kundzewicz. One option, which is for sure within the spirit of these days, would be to split the manuscript in several parts. On the other hand, I concur with your preference for exhaustive studies, which cover multiple aspects of the same problem, instead of limiting an analysis to a single key point, even if this is not fashionable these days. In likely case that you choose this second option, I strongly recommend to add a road map to the introduction of the manuscript, which clearly explains the various aspects which are covered in this paper. I also think it is necessary to better integrate those in a synoptic discussion, which helps the reader to grasp how they are interrelated. I think this can be achieved within a round of moderate revisions.
Best regards,

Erwin Zehe

Dear Dr. Koutsoyiannis,

in line with the reviewer I am very much pleased by the way how you addressed the reviewer comments in revision process. I see thus no reason to hold this work back from back final publication in HESS.

Best regards,

Erwin Zehe