Hydrological Effects of Urban Green Space on Stormwater Runoff Reduction in Luohe, China

Round 1

Reviewer 1 Report

Thank you for the opportunity to review "Hydrological effects of urban green space on stormwater runoff reduction in Luohe, China". I found the paper to be very well written with clear presentation of background, methods, and results. The authors make use of previous literature to support their results. 

While I enjoyed the presentation of the model results, I was left wanting more information of how the model calibrated to measured data. I encourage the authors to investigate if historical observations of streamflow, rainfall, climate, etc. are available and try to present cailbration/validation statistics before running future simulations. 

Minor comments are listed below:

1. The detail panels A and B in figure 2 are difficult to compare given the scale of the map. I do not think this figure is necessary.  
2. P. 5, line 175, spell out USGS
3. P. 5, line 178, round percentages to the nearest whole number. The amount of error in the model would preclude interpretation to the nearest 1/100. 
4. Section 2.4.2, it would be nice to have some explanation on what some of the long-term goals are for Luohe. Are there certain targets for runoff reduction established in an official document? 
5. Table 1. Round figures to the nearest whole number
6. Table 1, how will the impervious cover be reduced? I understand this is just a theoretical change but how would this likely happen in a real-world setting? For example, convert impervious parking lots to permeable pavement, retrofit roofs to green roofs, or convert vacant lots to green space. Are there any official plans to do this?
7. Section 3.1, a table showing the runoff reduction based on major changes in models scenarios would be helpful. For example, was the change in runoff volume achieved by reducing impervious cover greater than or less than the volume reduced by increasing the canopy over pervious cover? Was there any sort of parameter estimation or optimization done to the model?
8. P. 11, line 354, it's unclear what is meant by 'high-density' rainfall events
9. Figures 10 and 11, it is not clear these two figures are all that different. I would plot both lines on the same graph with common axes so the reader can easily see any differences. My suspicion is those differences are not very discernible. I would also do a non-parametric statistical test (i.e. Mann-Whitney) to determine if the differences are significant. 

Author Response

1.The detail panels A and B in figure 2 are difficult to compare given the scale of the map. I do not think this figure is necessary.  

Added two detailed sample figures to reveal the difference between the two figures in line 110

2.P. 5, line 175, spell out USGS

Added in line 175

3.P. 5, line 178, round percentages to the nearest whole number. The amount of error in the model would preclude interpretation to the nearest 1/100. 

Rounded 87.26%, 55.80%, 52.52% and 49.29%  to 87%, 56%, 53% and 49%, respectively in line 178

4.Section 2.4.2, it would be nice to have some explanation on what some of the long-term goals are for Luohe. Are there certain targets for runoff reduction established in an official document? 

Added some explanation at lines 202

There are no certain targets for runoff reduction in the official document

5.Table 1. Round figures to the nearest whole number

Rounded all the figures to whole numbers in Table 1

6.Table 1, how will the impervious cover be reduced? I understand this is just a theoretical change but how would this likely happen in a real-world setting? For example, convert impervious parking lots to permeable pavement, retrofit roofs to green roofs, or convert vacant lots to green space. Are there any official plans to do this?

Yes, the impervious cover could be reduced by old city renewal projects; the government plans to add more green spaces in the old district. A series of plans have been implemented by the government to replace the old or dilapidated low-rise buildings with high-rise buildings, and in the process to get vacant land to add more green spaces.

7.Section 3.1, a table showing the runoff reduction based on major changes in models scenarios would be helpful. For example, was the change in runoff volume achieved by reducing impervious cover greater than or less than the volume reduced by increasing the canopy over pervious cover? Was there any sort of parameter estimation or optimization done to the model?

The figure 6 was deleted and we added a table to show the major changes between the different scenarios.

Added more explanation in line 285

Yes, if the runoff volume drained by DCIA could be listed which will bring a clearer result regarding how much runoff generated in pervious and impervious cover separately, or if the pipe line system was involved in the model, and the results could be used in drainage system modification.

8.P. 11, line 354, it's unclear what is meant by 'high-density' rainfall events

Changed “high-density” into “high-intensity” in line 368

9.Figures 10 and 11, it is not clear these two figures are all that different. I would plot both lines on the same graph with common axes so the reader can easily see any differences. My suspicion is those differences are not very discernible. I would also do a non-parametric statistical test (i.e. Mann-Whitney) to determine if the differences are significant. 

Since the LAIs of leaf-on and leaf-off season are different, it would not make sense to plot the two lines in one graph. Here the two graphs were used to show the total trend of the interception efficiency in two seasons.

Reviewer 2 Report

The manuscript focuses on urban green space as way for regulating stormwater runoff. The document is well-structured and the rationale is clear. The Authors provide sufficient background in terms of scientific literature. The method has clearly been described by the Authors and appears to be replicable by other scholars. The findings are discussed in the light of previous studies and that is relevant to international audience. The English is good enough, but some typos need to be corrected. This reviewer feels that the contribution of the study to the international scientific panorama could be better explained by the Authors. In my opinion, the manuscript requires minor revisions and could be accepted for publication.

Minor revisions

Section 1. Introduction

The Authors clearly introduce the study and propose three research questions.

Line 62: the acronym “SWMM” has not been defined.

Section 2. Materials and Methods

The Authors report on study area, data and software, and justify their choices also in the light of previous studies developed by other scholars.

The references to Figure 2, 3, 4, 5, and 6 are missing in the main text of the manuscript. I would suggest the Authors refer to the figures in the main text of the manuscript and provide more details concerning them.

Line 189: “[...] and manually interpreted winter land-use map”. It is unclear what the Authors have done. Please consider explaining.

Section 3. Results and Discussion

It is unclear why the Authors “[...] selected [...] rain events consisting of 2.9 mm, 7.6 mm, 16.5 mm and 21.2 mm” (line 391). In other words, I would suggest the Authors explain why they use “2.9 mm, 7.6 mm, 16.5 mm and 21.2 mm” as magnitudes of rain events.

Lines 259-268: “The impervious cover decreased 11.14% in the final scenario over the base scenario, while the impervious runoff decreased 20%. The total impervious cover (bare impervious cover + impervious cover under tree canopy) declined from 61.26% in the current scenario to 58.24% and 55.24% in the future two scenarios. And the DCIA had the same decreasing trend with impervious cover. Decreasing impervious cover would result in decreased surface runoff. With decreasing DCIA, less impervious-generated surface runoff would continue over impervious cover all the way to the outlet, thus resulting in more water moving to pervious areas. The total pervious cover (impervious cover excluded) was increased from 38.74% 267 in the current scenario to 41.76% and 44.76% in two future scenarios”. Are the Authors referring to Table 1?

Line 351: the acronym “UHI” has not been defined.

Please check the label of the X axis in Figure 7.

Lines 309-311: “[...], while the monthly rainfall interception efficiency of existing UGS varied from 4% to 46% depending on the rain intensities in 310 summer seasons”. Is the variation “from 4% to 46%” retrieved from scientific literature or part of the findings?

Figure 12: It is unclear the meaning of “#” in the caption. Is it referring to the number of events? It is unclear the meaning of the X axis. In Figure 12a, the figures range from 1 to 6, in 12b from 1 to 10, in 12c from 1 to 12, and in 12d from 1 to 24. Please consider adding more details concerning Figure 12 than the ones in lines 393-407.

The findings are clearly discussed according to a critical approach, in the light of the results of previous research.

Section 4. Conclusion

Please consider recalling the research questions.

I would suggest the Authors point out the relevance of the study in terms of scientific contribution in the international panorama.

Author Response

Section 1. Introduction

The Authors clearly introduce the study and propose three research questions.

Line 62: the acronym “SWMM” has not been defined.

Added in line 63

Section 2. Materials and Methods

The Authors report on study area, data and software, and justify their choices also in the light of previous studies developed by other scholars.

The references to Figure 2, 3, 4, 5, and 6 are missing in the main text of the manuscript. I would suggest the Authors refer to the figures in the main text of the manuscript and provide more details concerning them.

Added the references in the main text. Line 107, 203, 205, 207

Line 189: “[...] and manually interpreted winter land-use map”. It is unclear what the Authors have done. Please consider explaining.

Added more explanation about how we calculated the percent of pervious and impervious cover under the tree canopy in line 204-206

Section 3. Results and Discussion

It is unclear why the Authors “[...] selected [...] rain events consisting of 2.9 mm, 7.6 mm, 16.5 mm and 21.2 mm” (line 391). In other words, I would suggest the Authors explain why they use “2.9 mm, 7.6 mm, 16.5 mm and 21.2 mm” as magnitudes of rain events.

Added more explanation in line 406-409

Lines 259-268: “The impervious cover decreased 11.14% in the final scenario over the base scenario, while the impervious runoff decreased 20%. The total impervious cover (bare impervious cover + impervious cover under tree canopy) declined from 61.26% in the current scenario to 58.24% and 55.24% in the future two scenarios. And the DCIA had the same decreasing trend with impervious cover. Decreasing impervious cover would result in decreased surface runoff. With decreasing DCIA, less impervious-generated surface runoff would continue over impervious cover all the way to the outlet, thus resulting in more water moving to pervious areas. The total pervious cover (impervious cover excluded) was increased from 38.74% 267 in the current scenario to 41.76% and 44.76% in two future scenarios”. Are the Authors referring to Table 1?

Yes, added a citation in line 279

Line 351: the acronym “UHI” has not been defined.

Added in line 365

Please check the label of the X axis in Figure 7.

Corrected the typo in line 310

Lines 309-311: “[...], while the monthly rainfall interception efficiency of existing UGS varied from 4% to 46% depending on the rain intensities in 310 summer seasons”. Is the variation “from 4% to 46%” retrieved from scientific literature or part of the findings?

Added in line 325-326

Figure 12: It is unclear the meaning of “#” in the caption. Is it referring to the number of events? It is unclear the meaning of the X axis. In Figure 12a, the figures range from 1 to 6, in 12b from 1 to 10, in 12c from 1 to 12, and in 12d from 1 to 24. Please consider adding more details concerning Figure 12 than the ones in lines 393-407.

Change “#” to “NO.” in line 429-431 and in Fig. 12.  Yes, the # is referring to the number of rain events. The X axis shows the duration time of rain events.   More details concerning figure 12 were added in line 412-413.

The findings are clearly discussed according to a critical approach, in the light of the results of previous research.

Section 4. Conclusion

Please consider recalling the research questions.

Added a sentence to recalling the research questions in line 482

I would suggest the Authors point out the relevance of the study in terms of scientific contribution in the international panorama.

Added a sentence to show the scientific contribution in the international panorama at lines 499-502.

Reviewer 3 Report

The paper is very interesting, though the used methodology needs to be better explained.

The different methodological steps need to be described, and a phased methodological diagram is highly recommended.

Conclusions need to be more scientific. As they are they highlight the limitations of the research.

Author Response

The paper is very interesting, though the used methodology needs to be better explained.

Added more detail to the methods (also in response to other reviewers’ comments). In line 205-206 and line 211

The different methodological steps need to be described, and a phased methodological diagram is highly recommended.

Added a phased diagram to show the steps in line 183-197

Conclusions need to be more scientific. As they are they highlight the limitations of the research.

Unfortunately, we were not able to make revisions because we did not understand this comment (what is meant by “more scientific”?). Can the reviewer please be more specific?