Dear Dr. Webber,

I have now read carefully your ms. along with the evaluation of two anonymous reviewers and your succinct answers to their comments.

After careful consideration, I think that the ms. in its present form does not warrant publication for HESS. You have made the choice of using an auto-regressive model (instead of a physically-based one) to identify the duration of salinity intrusion periods and their potential impact for the freshwater supply for the Shanghai urban area. We concur to identify this aspect of your research as the novel component. This is however a little bit slim as the focus is only on the identification (and not on the prediction) of such events and it is hard to envision how these results could support risk assessments studies resulting from hydraulic management or induced by, e.g., climate change.

If you decide not to follow the suggestion of reviewer 1 to apply a more physically based model, I would then like that you elaborate fully in the revised ms. on how your auto-regressive model can cope with his comment nr 4 (stated differently, management issues should be treated in THIS paper; and not in a companion paper as suggested in lines 15-20 of your intro). This would then allow to use your model in a prognostic mode, thereby increasing significantly the value of your study. It would also be needed to expand significantly on his comment nr 5 (the extend to which the auto-regressive model can help identify causes of changes in the duration of salt intrusion such as spill-overs).

Kind regards,

Pierre Regnier AE

Dear authors,

The substantial changes that have been made to your paper, and the detailed way in which the comments have been considered have significantly improved the significance and quality of your ms. I am thus pleased to recommend your contribution for publication to HESS.