The review process of this paper was extremely lengthy, which yielded only one useful review.
In total 20 experts were invited to review this paper. Most did not even bother to decline the invitation. Given the poor quality of reviewer #2, the long wait for a second reviewer did not pay off. I apologise for this extreme delay.

Having said this, I am generally happy with how the authors have responded to the critical comments of reviewer #1.

I have one comment to add: In my opinion, the abstract and the conclusions should include the important statement in the discussion that the model outcomes “need to be considered optimistic” (lines 508 - 509) because of two major reasons: (1) there is generally still uncertainty about the effect of high CO2 on cotton yields and water use, simply because of a lack of sufficient empirical experiments; and (2) the model used in this paper does not include the negative effects of heat-days with temperatures above 35 Celsius, which is known to lead to boll abscission and thus to lower cotton yield.

On a side note, I found the sentence in lines 40-43 in the abstract confusing, as it refers to "climate change effects" only, but it does not state this. Also, I found the reference to the Aral Sea in the abstract not warranted.

There are a few typos/grammar issues that also need to be addressed (e.g. lines 157, 274, 295, 342,380.

I look forward to receiving an improved version of the manuscript.

Pieter van der Zaag

Dear authors,

I am happy with the meticulous manner you have responded to the reviewer's comments and my own. I therefore recommend the paper to be accepted for publication in HESS.

Once again my sincere apology for the long duration of the review process.

Pieter van der Zaag