|I was already reviewer for the first version of the manuscript submitted. The revised version exhibits some significant improvements which are satisfactory. However all points were not addressed, and I believe that some minor modifications are still needed before the paper is suitable for publication in HESS. |
- Some comments of the reviewers or the editor are said to be mentioned in the answer of the authors but are not really addressed in the new manuscript (ex: EC3 - the potential uncertainty of models are not really discussed in the text, neither climate change in the introduction; EC5 – the answer to this is not found in the text). This is quite annoying and should be changed in the revised manuscript (reading again the comments on the first version on the manuscript)
- I still believe it would be relevant to include one hydrograph for at least one event with flow simulated for various resolutions. It would complement well the discussion based on relative values (because as mentioned in the discussion, the highest relative deviations are found for the event 4 which is generating the less runoff).
- Few words on the model validation should be added, to justify the fact that it is legitimate to use it for such a study.
p.4 l.17-21 : given that there is a precise list of questions, we would expect a similar presentation in the conclusion to answer them. l.18 “urban drainage model” is too general in the question, may be you should use “highly detailed semi-distributed model”.
2) Presentation of the case study
p.5 l.19-20 : a map of the catchment with all the runoff areas (the location of the study area within the Rotterdam region could also be indicated in this figure) could be helpful. More quantitative information is given anyway after with the “model lengths” section.
2.2 rainfall data : I am not sure, but I do not think Rotterdam is within the range of the CESAR radar so you should explain how you selected the portion of studied rainfall event and where you implemented it over the catchment (i.e. where and why did you apply the heaviest rainfall).
p.8 l.11 : “spatially aggregated”, how was it done? Simply the mean over various pixels or the aggregation is done on radar data before implementing a Z-R relationship. I think it should be explained.
Eq. 1 : is it done on rainfall rate or radar reflectivity (if not the Z is a bit confusing and should be modified).
Figure 4 : indicate what represent the axis
p.8 l.27 : “the magnitude of the distance”; this expression is not clear. Please change.
Dimensionless parameters: include systematically the equation to help the reader
p.11 l.15-16 : use “length” rather than “resolution” because the parameters were introduced as lengths.
3.2.4 : l.28 : “which corresponds to the inverse of a sewer density”. I do not understand this, given definition of the sewer density in 3.1.3. How two quantities with the same physical dimension (a length) can be inverse? Why defining the sewer length LS before and not using it?
4) Results and discussion
p.13 l.7-17 : comments and physical interpretation that would ease the reading should also be added, only stating the figures is not enough.
p.13 l.22-23 : it would help the reader if you just said that it was obtained for various rainfall resolution and that no hydrological modelling are used. Figure 5 : the “vs.” are reversed in the caption and not in the manuscript (other figure captions should also be checked). The legend says mean over the pixels, and the text over the catchment please clarify. From my understanding it is not “standard deviation of normalized rainfall volume” but “normalized standard deviations of rainfall volumes” (as said after by the way). Authors should be much more careful with the words; such imprecise vocabulary make it much harder to understand, and this was already mentioned in the previous reviews !!
p.13 l.28-30 : as said in my previous review (and this has not been addressed), the decrease is due to the artificial transfer of rainfall outside the boundary of the catchment. It could be the other way if the heaviest portion of the storm was outside. So I am not sure that the tendency is really relevant, but the order of magnitude are and this should be stressed. By the way this effect is explained at the sub-catchment scale in sections 4.1.4 and 4.1.5, so it should also be discussed here as well. I think is should also be changed in the abstract.
p.14 l.15-16 : “a more pronounced internal spatial structure” what does it mean and how did you obtained that (there is only a 50m differences in storm decorrelation length). The expression is also used after in the section and the meaning should be explained there as well.
p.14 l.21 : a clear reduction “of” the median
p.15 l.9 : check sentence because not clear
4.1.3 : given that the results are used in the discussion of the previous sub-section (which uses the storm structure), I would suggest to move it before. Figure 8: include the event number in the figure (the “going clockwise” of the caption is not “user friendly” for the reader)
4.1.4 : the “in-sewer” in the title is a bit confusing because it is also the case in section 4.1.2
p.17 l.14-15 : “deviations ... increasing” is not clear. Are you mentioning a monotonic trend in the curves ?
p.17 l.28 : it is not clear to me how the threshold of 0.5 was obtained (I already mentioned this issue in my previous review and this was not addressed).
4.1.5 : again from Figure 10, the threshold of 20 mentioned in the text seems rather arbitrary and should be justified (not obvious from the rather steady trends Fig. 10) or simply not used.
p.18 l.17 : 900m of pipes per 100m2 seems rather high, is not it 100m*100m