Detailed Quantification of the Reduction Effect of Roof Runoff by Low Impact Development Practices

Round 1

Reviewer 1 Report

The article deals with the need to reduce the runoff from urban areas, which is now mandatory in the design and renovation of buildings.
it is quite evident that the increase in true surfaces implies such a reduction. In the article, however, the use of optimization methods is interesting, which has had considerable success and which may be of interest to other researchers and designers.
Minor: lines 453 and 454.

Author Response

Reply to Reviewer Comments 1#: 1.Minor: lines 453 and 454. Our respond: Thank the reviewer for affirmation to this paper. We overlooked this in the original version of our manuscript and thank the reviewer for bringing these points to our attention. The sentence “This section is not mandatory, but can be added to the manuscript if the discussion is unusually long or complex.” in line 453-454, page 18 of original manuscript has been deleted in the revised manuscript.

Reviewer 2 Report

Generally, the paper is well written and structured, however I think it needs some improvements prior the publication. More in detail please find below, section by section, my observations and comments.

Introduction: In general the Introduction is well written and organized, and coherent with the proposed study.

My only doubt it is what the authors mean by “Low elevation greenbelts”; I know the Greenbelts and their principle functions, but I can't understand what the authors mean by "low elevation"..Please clarify.

Page 2, Lines 61-62: I would suggest authors to insert some more reference and newer: the most recent of the 3 cited dates back to 8 years ago.

Materials & Methods: In general Section 2 (Methodology) describes each phase of the whole approach in a detailed, orderly and punctual way. My greatest consideration is about the several "previous articles" (eg. 31, 42, 43) that authors cited, without giving adequate information that would be helpful to the reader to better follow the text...therefore please add some reminder od additional informations.

Section 2.1: My only doubt is about the percentage of the three main land use type (roofs, green fields and pavement): looking Fig. 2 the impermeable surface it seems much higher (dark gray and pathways in light gray); I don't understand if the % relative to Pavement also includes roads or not.

P4, Line 118: The authors say that "the model has been widely applied in THOUSANDS of studies" but cited only 3 study…the sentence is not supported..I suggest to add some more references.

P5, Lines 141-142: How do the authors justify the 6 hour interval to define separate events? I suggest seeing, and eventually inserting, these References who made the same choice:

• Stovin, V., Vesuviano, G., & Kasmin, H. (2012). The hydrological performance of a green roof test bed under UK climatic conditions. Journal of hydrology, 414, 148-161.
• Palermo, S. A., Turco, M., Principato, F., & Piro, P. (2019). Hydrological effectiveness of an extensive green roof in Mediterranean climate. Water, 11(7), 1378.
• Voyde, E., Fassman, E., & Simcock, R. (2010). Hydrology of an extensive living roof under sub-tropical climate conditions in Auckland, New Zealand. Journal of hydrology, 394(3-4), 384-395.

P5, Lines 142-143: Despite the detailed information on the events are reported in the cited text (Ref. 31), I suggest to insert a small reminder table that facilitates the reading of this text

Page 5, Lines 146: The authors says that "the parameters were set based on previous research (33-35)", but these are studies with different stratigraphic characteristics (growing media, filter and drainage layer). In my opinion, to obtain consistent and realistic results, should be used the specific parameters of each material chosen (technical specifications) or carry out laboratory tests that measure the specific parameters

Table 1: It is not clear what is the Green Roof's Soil thickness. Why In Table1 is 100 mm (and not 120 mm), if in the previous description of the green roof module (Lines 146-147) the growing medium was 12 cm? Please explain

P5, Lines 167: Despite the catchment model was established in a previous cited text (Ref. 31), I suggest to give some indication about it that facilitates the reading of this text. At least I would add a figure that schematizes the catchment network.

NB:The authors will still find this same comment for all other references to previous articles, just mentioned.

P5-P6: With regard to the NS coefficient, used to evaluate the model's performance, I suggest adding the ranges of variation of the values (for easier understanding of the reader and to find a match in Table 3).

PFE & VE: The authors wtite "PF & V Error" because they mean the error of the simulated value with respect to the observed value? Right? But I think these two parameters are not suitable for evaluating the performance of the model. Statistical indexes able to to describe the model general performance are NS (used by the authors), Percent Bias (PBias) - wich measures the average tendency of the model to overestimate or underestimate the counterpart - Standard deviation Ratio (RSR). I suggest to consult: Moriasi et al., 2007 “Model Evaluation Guidelines for Systematic Quantification of Accuraccy in Watershed Simulations”.

Section 2.4: I'm not sure I understood the difference between building-scale and campus-scale simulations with respect to combined scenarios. I mean… at BUILDING SCALE the authors choose the surface occupied by a building’s roof (520 m2) and combine multiple LID techniques in that area, right? Instead, at CAMPUS SCALE, why the authors consider only a portion of the total 58 ha of the campus and not all? In Table 2, there are scenarios with a Total area that varies from a min. of 2220 m2 to a maximum of 255246m2 (25ha) compared to the 58ha total… It would be appropriate to schematize graphically the scenarios shown in Tab2, and select the areas in which each scenario intervenes.

In addition I believe that to be a correct comparison, should be used the same reference area and intervene on it with different LID% for each scenario

Section 2.5.1: It is not clear if with "reduction ability of LID" the authors mean Retention capacity? Please clarify

P8, Lines 210-211: What the authors mean by “This indicator can easily reflect the effect of runoff control”?

Section 2.5.3: How is the term Bi (Benefit of the scenario) of the Cost-effectiveness equation obtained?

P9, Linea 244-245: As already commented more times, please give some more information about calculation process findable in the reference (42) cited, to facilitate reading and understanding of the text.

P9, Lines 252-253: Look at the comment above: please give more information about reference 43

Results & Discussion: In general the results are well related to each phase described in previous section and the discussion highlights the main results and is coherent with them. However, I believe that some minor changes should be made, first of all add the hydrological features of each storm event in Tables.

Section 3.1: The Observed data (Figure 3) are those relating to the experimental blocks, right?

Table 3: As already said and justified in a previous comment I believe that these two parameters (PFE and VE) are not suitable for evaluating the performance of the model and also the results reported in the Table 3 seem to show my doubt about it. It would be more appropriate to assess these parameters in relation to a conventional roof (Normal Roof) as:

- Peak Flow Reduction (or hydrograph attenuation), which could be expressed as the percentage difference between the Normal Roof peak flow and the simulated/modelled GR peak flow;

- Runoff Attenuation (Volume Reduction) calculated as the absolute percentage difference between the Runoff volume from the Normal Roof and the discharged volume from the modelled/simulated GR.

Section 3.2: To better evaluate the hydrological performance of individual LID practices, and comment obtained results (Table 4), it would be appropriate to indicate the Hydrological characteristics of each selected rainfall event: Precipitation Depth, Rainfall Duration and Mean Rainfall Intensity.

P11, Line 288: Why the results relating to the scenarios RB-8 and LG-100% are not shown in Table 4? No outflow occur for both scenarios? Anyway, Please add the results of these scenarios, as in the following lines (Lines 296-300) these results continue to be commenting (but not read)

P11, Line 289-290: Authors claim that "results suggesting that green roofs and greenbelts have a limited ability to cope with heavy events"; I believe that before coming to a conclusion, however not to be excluded, it is necessary consider the hydrological features of each storm event [precipitation depth (PD), rainfall duration (D), rainfall intensity (i)] and the antecedent dry weather period (defined as the dry weather period between two independent rainfall events), which affects the initial soil moisture condition and therefore the soil retention capacity. The same authors, a few lines later (Lines 309-311), claim that the rainfall characteristics affect on performance indicators.

Table 4, Table 5, Table 6, Table 7 and Table 9: As already said, please add the hydrological features of each storm event.

Section 3.5: I would add a few more considerations

Conclusions

P18; Lines 453-454: I believe that the conclusions section is necessary

Author Response

Dear Editor, Thank you very much for your email of February 23, 2020, informing us of valuable suggestions to improve our manuscript ‘Detailed Quantification of the Reduction Effect of Roof Runoff by Low Impact Development Practices’. We would like to thank the reviewers for their thoughtful review of this manuscript. The comments and suggestions are very helpful for improving the manuscript. We have revised our manuscript accordingly. Our point-by-point responses are as follows. Reply to Reviewer Comments 2#: 1.English language and style are fine/minor spell check required  Our respond: Thank the reviewer for pointing out it. The article has been checked thoroughly and the following modification has been made. “-” has been deleted in the sentence “This study provides an important reference for urban water management and LID-related decision making.” in line 31, page 1 in revised manuscript. “-” has been deleted in the sentence “This study lays the foundation for LID planning at the building scale and can provide good support for LID-related decision making.” in line 92, page 3 of revised manuscript. “-” has been modified to “to” in the sentence “The campus is flat overall, and its elevation ranges from 47.5-52.9 m.” in line 108, page 3 of revised manuscript. “a” has been added before “height” in the sentence “The parameters of the rain barrel were set based on the real rain barrel used on the campus, with a basal area of 3 m2 and height of 2 m for each barrel.” in line 169, page 5 of revised manuscript. “as” has been modified to “to” in the sentence “The parameters of the low elevation greenbelt were set to be identical to those of the greenbelt except that the berm height was set as 150 mm.” in line 173, page 5 of revised manuscript. “were” has been modified to “was” in the sentence “A total of 749 subcatchments were delineated with roofs, greenbelts, roads, sports fields, asphalt pavement and concrete pavement types.” in line 181, page 6 of revised manuscript. “is” has been modified to “was” in the sentence of “The rain barrel scenario means that roof runoff was directed into the rain barrels.” in line 207, page 7 of revised manuscript. “combined” has been modified to “combination” in the sentence “The specific area of each LID application in the combined scenarios was adjusted according to its reduction performance.” in line 218, page 7 of revised manuscript. “fr,n” has been modified to “fr,t” In the sentence “fr,n is the present value factor of the discount rate r in year t” in line 286, page 9 of revised manuscript. “is” has been modified to “was” in the sentence of “The US dollar is taken as the unit of cost in this study.” in line 287, page 9 of revised manuscript. “s” has been added after “zero” in the sentence “While the intensity of artificial rainfall was 29 mm/h, the simulated and observed outflows were all zero.” in line 304, page 10 of revised manuscript. “s” has been added after “fit” in the sentence “Figure 3 shows that the simulated hydrological response fit well with the observed values.” in line 304, page 10 of revised manuscript. The sentence “Limiting the amount of soil on green roofs and the infiltration rate for greenbelts limit the volume reduction abilities of these two practices.” has been modified to “The limited amount of soil in green roofs and the restricted infiltration rate for greenbelts constrain the volume reduction abilities of these two practices.” in line 346-348,page 12. “combined” has been modified to “combination” in the sentence “There was no outflow in the other rainfall events for all combined scenarios.” in line 372, page 12 of revised manuscript. “combined” has been modified to “combination” in the sentence “Figure 5 shows that the combined scenarios can effectively control all rainfall events with fewer areas of composed LID.” in line 375, page 13 of revised manuscript. “combined” has been modified to “combination” in the sentence “In the storm event of 08-31-2014, all combined scenarios had outflow.” in line 377, page 13 of revised manuscript. “combined” has been modified to “combination” in the sentence “The performances of the combined scenarios are summarized in Table 6.” in line 378, page 13 of revised manuscript. “combined” has been modified to “combination” in the sentence “Based on the volume reduction amount in the event of 08-31-2014, the ranking of the combined scenarios is GR&RB&LG > RB&LG > GR&LG > GR&RB.” in line 389, page 13 of revised manuscript. “as” has been modified to “to” in the sentence “The unit construction cost and percent of cost for unit operation and maintenance were set as 280-340 dollars/m2 and 1%, respectively [54].” in line 443, page 16 of revised manuscript. “as” has been modified to “to” in the sentence “The service life of all LID practices was set as 20 years [48, 54]” in line 444, page 16 of revised manuscript. “could have” has been deleted in the sentence “It can be seen in Table 10 that individual and combined LID practices implemented to reduce roof runoff could have effectively reduced the outflow and overflow of the campus in 2017.” in line 490, page 19 of revised manuscript. “Normal” has been added after “Beijng” in the sentence “X.H. developed the campus model of Beijing Normal university” in line 539, page 20 in Author Contributions section of revised manuscript. “Cities-Contruction” has been modified to “Cities-Construction” in the reference name of “Technical Guide for Sponge Cities-Construction of Low Impact Development” line 567, page 20 in revised manuscript. 2.Introduction: In general the Introduction is well written and organized, and coherent with the proposed study. My only doubt it is what the authors mean by “Low elevation greenbelts”; I know the Greenbelts and their principle functions, but I can't understand what the authors mean by "low elevation".Please clarify. Our respond: Thank reviewer for inquiring. Low elevation greenbelt has been listed as one of LID practices in “Technical Guide for Sponge Cities-Construction of Low Impact Development” (MHURD, 2014) released by Ministry of Housing and Urban Rural Development of China. In this technical guide, low elevation greenbelt is defined as greenbelt whose surface is below surrounding ground or road. It has extra storage space to temporarily store rainwater comparing with normal greenbelt. Its effect has also been studied in the article of “Comprehensive benefit evaluation system for low-impact development of urban stormwater management measures” by Li et al., (2017). 3.Page 2, Lines 61-62: I would suggest authors to insert some more reference and newer: the most recent of the 3 cited dates back to 8 years ago. Our respond: Thanks for bringing this point to our attention. Two newer references “Evaluating the Hydrologic Benefits of a Bioswale in Brunswick County, North Carolina (NC), USA” published in 2019 by Purvis et al. and “Assessing the Retention Capacity of an Experimental Green Roof Prototype.” published in 2020 by Silva et al. have been added in line 67, page 2, in the main text and in line 592-596, page 21 in the reference section of revised manuscript accordingly. Other number of references in main text and reference section has been modified successively. 4.Materials & Methods: In general Section 2 (Methodology) describes each phase of the whole approach in a detailed, orderly and punctual way. My greatest consideration is about the several "previous articles" (eg. 31, 42, 43) that authors cited, without giving adequate information that would be helpful to the reader to better follow the text...therefore please add some reminder od additional informations. Our respond: We overlooked this in the original version of our manuscript and we thank the reviewer for noticing it. The sentence “Detailed information on these eight rainfall events can be found in our previously published paper [31]” has been deleted in the revised manuscript and a new table, Table 1, has been added in line 152, page 5 of revised manuscript to provide the detailed hydrological features of selected rainfall events. The number of other tables has been revised successively. The sentence of “A detailed calculation process can be found in our previous paper [42]” has been modified to “The detailed computing formula of fr, t, and SVn can be found in previous paper [48].” in line 288, page 9 of revised manuscript. The sentence of “A detailed description of this algorithm can be found in a previous article [43]” has been modified to “A detailed description of the principle and main loop of this algorithm can be found in a previous article [49]” in line 296-297, page 9 of revised manuscript. 5.Section 2.1: My only doubt is about the percentage of the three main land use type (roofs, green fields and pavement): looking Fig. 2 the impermeable surface it seems much higher (dark gray and pathways in light gray); I don't understand if the % relative to Pavement also includes roads or not. Our respond: We overlooked this in the original version of our manuscript and we thank the reviewer for noticing it. The sentence of “The three main land use types are roofs, green fields and pavement, which account for 30%, 25% and 19%, respectively, of the total area of the campus.” has been modified to “The three main land use types are pavement, roofs and green fields, which account for 31.9%, 30.3% and 25.2%, respectively, of the total area of the campus” in line 106, page 3 of revised manuscript. In our previous study of hydrological simulation of the campus of Beijing Normal university, the land use was divided into eight kinds i.e. building roof, green space, concrete pavement, asphalt road, permeable pavement, sport Ⅰ, sport Ⅱand others, which account for 30.3%, 25.2%, 18.7%, 11.2%, 1.9%, 4.4%, 4.9%, 3.3%, respectively, of the total area of the campus. In the revised manuscript, the sum of the percent of concrete pavement, asphalt road and permeable pavement was calculated to be 31.9% and provide as the total percent of pavement. 6.P4, Line 118: The authors say that "the model has been widely applied in THOUSANDS of studies" but cited only 3 study…the sentence is not supported.I suggest to add some more references. Our respond: We overlooked this in the original version of our manuscript and we thank the reviewer for noticing it. The word “thousands of” has been modified to “hundreds of” in line 125, page 4 of revised manuscript based on a review of SWMM, A reference of a review of SWMM, “Storm water management model: performance review and gap analysis” published in 2017 by Niazi et al. and two newest application reference of SWMM, “Optimal Planning of Low-Impact Development for TSS Control in the Upper Area of the Cau Bay River Basin, Vietnam” published in 2020 by Minh Hai and “Hydrological Modelling and Evaluation of Detention Ponds to Improve Urban Drainage System and Water Quality” published in 2019 by Souza et al. have been added in line 126, page 4 in main text and line 627-634, page 22 in reference section in revised manuscript accordingly. 7.P5, Lines 141-142: How do the authors justify the 6 hour interval to define separate events? I suggest seeing, and eventually inserting, these References who made the same choice: Stovin, V., Vesuviano, G., & Kasmin, H. (2012). The hydrological performance of a green roof test bed under UK climatic conditions. Journal of hydrology, 414, 148-161. Palermo, S. A., Turco, M., Principato, F., & Piro, P. (2019). Hydrological effectiveness of an extensive green roof in Mediterranean climate. Water, 11(7), 1378. Voyde, E., Fassman, E., & Simcock, R. (2010). Hydrology of an extensive living roof under sub-tropical climate conditions in Auckland, New Zealand. Journal of hydrology, 394(3-4), 384-395. Our respond: Thanks for the reviewer’s thoughtful comment and detail suggestion. The three references have been inserted to revised manuscript in line 151, page 5 in main text as reference 34-36 and line 638-644, page 22 in reference section accordingly. 8.P5, Lines 142-143: Despite the detailed information on the events are reported in the cited text (Ref. 31), I suggest to insert a small reminder table that facilitates the reading of this text Our respond: Thanks for the reviewer’s suggestion. The sentence “Detailed information on these eight rainfall events can be found in our previously published paper [31]” in line 142-143 of the original manuscript has been deleted in the revised manuscript. A new table of rainfall features has been added in line 152 page 5 as Table 1 in the revised manuscript according reviewer’s suggestion. 9.Page 5, Lines 146: The authors says that "the parameters were set based on previous research (33-35)", but these are studies with different stratigraphic characteristics (growing media, filter and drainage layer). In my opinion, to obtain consistent and realistic results, should be used the specific parameters of each material chosen (technical specifications) or carry out laboratory tests that measure the specific parameters Our respond: Thank the reviewer for bringing it to our attention and give us valuable suggestion. The method suggested by reviewer is a perfect way to establish LID model. However, in the artificial rainfall experiment of this study, only the initial water content was measured using a soil moister meter TDR. The other parameters are determined based on suggestive values of the model and previous article and calibrated using observed time series of outflow in 5 minute interval in different level of rainfall intensity. 10.Table 1: It is not clear what is the Green Roof's Soil thickness. Why In Table1 is 100 mm (and not 120 mm), if in the previous description of the green roof module (Lines 146-147) the growing medium was 12 cm? Please explain Our respond: We overlooked this in the original version of our manuscript and thank the reviewer for bringing these points to our attention. The value of soil thickness was mistakenly provided in the original manuscript. The value of “12 cm” has been modified to 10 cm in line 156, page 5 in revised manuscript. 11.P5, Lines 167: Despite the catchment model was established in a previous cited text (Ref. 31), I suggest to give some indication about it that facilitates the reading of this text. At least I would add a figure that schematizes the catchment network. NB:The authors will still find this same comment for all other references to previous articles, just mentioned. Our respond: Thank the reviewer for bringing it to our attention and give us valuable suggestion. The network of the catchment has been shown in supplemental material as Figure S1 accordingly. The sentence “The catchment model was established in our previous study [41]” has been modified to “The catchment model was established in our previous study [41] and the network of the catchment can be found in Figure S1 in supplemental material.” in line 178-179, page 6 in revised manuscript. 12.P5-P6: With regard to the NS coefficient, used to evaluate the model's performance, I suggest adding the ranges of variation of the values (for easier understanding of the reader and to find a match in Table 3). PFE & VE: The authors write "PF & V Error" because they mean the error of the simulated value with respect to the observed value? Right? But I think these two parameters are not suitable for evaluating the performance of the model. Statistical indexes able to describe the model general performance are NS (used by the authors), Percent Bias (PBias) - which measures the average tendency of the model to overestimate or underestimate the counterpart - Standard deviation Ratio (RSR). I suggest to consult: Moriasi et al., 2007 “Model Evaluation Guidelines for Systematic Quantification of Accuraccy in Watershed Simulations”. Our respond: Thank the reviewer for bringing it to our attention and give us valuable suggestion. The evaluation parameter of PFE and VE has been replaced by PBIAS to better evaluate the simulation result. The equations of PFE and VE has been deleted and the sentence “Qo,p is the observed peak flow rate (m3/s). Qs,p is the simulated peak flow rate (m3/s). Vo is the observed total flow rate (m3). Vs is the simulated total flow rate (m3).” has also been deleted. The equations of PBIAS has been added in line 189, page 6 of revised manuscript. The number of equations has been revised successively. The sentence “The Nash-Sutcliffe efficiency coefficient (NSE), deterministic coefficient (R2), peak flow error (PFE) and volume error (VE) were calculated to evaluate the model result. The equations of NSE, R2, PFE and VE are as follows:” has been modified to “The Nash-Sutcliffe efficiency coefficient (NSE), deterministic coefficient (R2) and percentage of bias (PBIAS) were calculated to evaluate the model result. The equations of R2 and PBIAS are as follows:” in line 187-189, page 6 of revised manuscript. The sentence “The results of calibration and validation for the hydrological module of SWMM in BNU are shown in Table 3.” has been modified to “The information of selected rainfall events, observed outflow at outfall-3, and the results of calibration and validation for the hydrological module of SWMM in BNU are shown in Table 4.” in line 310-312, page 10 in revised manuscript. The values of PBIAS have been provided in Table 4 in line 313, page 10 of revised manuscript. The observed total outflow and peak flow rate has also been provided in Table 4 to reflect the range of observed values. The sentence “PFE ranged from -30.2% to -8.9% and VE ranged from -36.5% to -6.8% for rainfall events in 2014 during the calibration process.” has been modified to “PBIAS ranged from -15.96% to 2.26% for rainfall events in 2014 during the calibration process.” in line 314, page 10 of revised manuscript. The sentence “PFE ranged from -53.8% to -13.2% and VE ranged from -25.6% to -2.3% during the validation process.” has been modified to “PBIAS ranged from -17.97% to -1.95% during the validation process.” in line 316, page 10 of the revised manuscript. 16.Section 2.4: I'm not sure I understood the difference between building-scale and campus-scale simulations with respect to combined scenarios. I mean… at BUILDING SCALE the authors choose the surface occupied by a building’s roof (520 m2) and combine multiple LID techniques in that area, right? Our respond: Thank reviewer for inquiring. Yes, at building scale, combined LIDs were applied to the 4th teaching building with roof area of 520 m2. 17.Instead, at CAMPUS SCALE, why the authors consider only a portion of the total 58 ha of the campus and not all? In Table 2, there are scenarios with a Total area that varies from a min. of 2220 m2 to a maximum of 255246m2 (25ha) compared to the 58ha total… It would be appropriate to schematize graphically the scenarios shown in Tab2, and select the areas in which each scenario intervenes. Our respond: Thank reviewer for inquiring. This study focuses on LID which can reduce roof runoff, i.e. rain barrel, green roof and greenbelt, to study their effect of roof runoff reduction in building scale and campus scale. So, at campus scale, only LID aiming at roof runoff reduction was added and studied in SWMM model of the campus. The areas in Table 2 (Table 3 in revised manuscript) is the areas occupied by roof related LID, mainly include area of flat roof on which green roof can be applied, green space on which green belts and low elevation greenbelts were applied and rain barrel. For example, 2220 m2 is the area covered by rain barrel in rain barrel scenario. In addition, it is hard for LID to cover all surface of the campus to be 58 ha. The figure of occupied area of scenarios, i.e. flat roof and green space, has been provided in Figure S1 of supplemental material according to reviewer’s valuable suggestion. The area of rain barrel is hard to be shown in a figure as their covered area are too small to be shown. The sentence “Detailed scenario settings can be seen in Table 2.” has been modified to “The areas covered by LID scenarios on the campus can also be seen in Table 3 and Figure S1 in supplemental material.” in line 244-245, page 7 in revised manuscript. 18.In addition I believe that to be a correct comparison, should be used the same reference area and intervene on it with different LID% for each scenario Our respond: Thanks for the reviewer’s valuable suggestion. The reference area of green roof and greenbelt was set to be the same of 520 m2. It is hard for rain barrel to be applied in the same area because of its implementation property. The reviewer’s suggestion is a correct way to simulate LID and our scenarios were set in this way during initial steps. The scenarios were then adjusted based on the simulated result of these scenarios to make sure that the scenarios have outflow in the studied rainfall events and return period and their effect can be analyzed, the effect of composed LID can be displayed and avoid too many scenarios were presented. 19.Section 2.5.1: It is not clear if with "reduction ability of LID" the authors mean Retention capacity? Please clarify Our respond: Thank reviewer for inquiring. “Reduction ability of LID” was used in this study to represent the capacity of LID to reduce runoff. As the reviewer’s suggestion, “retention capacity” are frequently used to represent the capacity of LID to reduce runoff. For example in the article of “Evaluating retention capacity of infiltration rain gardens and their potential effect on urban stormwater management in the sub-humid loess region of China” (Tang et al., 2016)) by Tang et al. published in 2016, the retention capacity of rain garden was evaluated by flow reduction rate: Where win is the inflow and wout is the overflow of rain garden. In this sense, “retention capacity” has the same meaning with “reduction ability” used in our paper. On the other hand, in our opinion, retention is also frequently used to represent the capacity of LID media to keep water. For example, in the paper of “A modelling study of long tern green roof retention performance” (Stovin et al., 2013) by Stovin et al. published in 2013, it is said that “The difference between field capacity and permanent wilting point determine the maximum stormwater retention capacity of the green roof”. In this sense, retention is parallel with other runoff reduction process such as infiltration, storage and evaporation. In our paper, the sentence “Green roofs mainly rely on soil retention, and greenbelts mainly rely on soil retention and infiltration to reduce runoff volume.” was included and the processes of infiltration and evaporation were simulated in SWMM to reflect the total reduction effect of LID. As a result of that, “reduction ability” was used in our paper to avoid confusion. In addition, “retention” was seldom used to describe the reduction capacity of rain barrel. As LID applied in this study include green roof, rain barrel and greenbelt, “reduction ability” was used to generalize their capacity to reduce runoff. 20.P8, Lines 210-211: What the authors mean by “This indicator can easily reflect the effect of runoff control”? Our respond: Thank reviewer for bringing this point to our attention. The sentence has been modified to “This indicator can directly reflect how much percent of runoff is reduced by LID.” in line 252-253, page 8 in the revised manuscript to make it better to be understood. 21.Section 2.5.3: How is the term Bi (Benefit of the scenario) of the Cost-effectiveness equation obtained? Our respond: Thanks for the reviewer’s inquiring. Bi is the benefit of the ith scenario. It is the difference between total outflow of NR and ith scenario in building scale. The sentence “The volume reduction in the LID scenarios compared to the NR scenario at the building scale in 2017 was calculated and demonstrates the benefits of LID.” in line 235-236, page 8 of the original manuscript has been modified to “The volume reduction in the LID scenarios compared to the NR scenario at the building scale in 2017 was calculated and used to represent the benefits of LID.” in line 279, page 9 of the revised manuscript to facilitate reading. 22.P9, Linea 244-245: As already commented more times, please give some more information about calculation process findable in the reference (42) cited, to facilitate reading and understanding of the text. Our respond: We overlooked this in the original version of our manuscript and thank the reviewer for bringing these points to our attention. The word “[42]” in the sentence “Cost-effectiveness was calculated based on the following equation [42]” in original manuscript has been deleted in line 282, page 9 in the revised manuscript as the equations we provide are not the same as equations in reference (42). The sentence of “A detailed calculation process can be found in our previous paper [42]” in line 244-245 of original manuscript has been modified to “The detailed computing formula of fr, t, and SVn can be found in previous paper [48].” in line 288, page 9 of revised manuscript to facilitate reading. 23.P9, Lines 252-253: Look at the comment above: please give more information about reference 43 Our respond: Thanks for the reviewer’s suggestion. According to reviewer’s previous suggestion, the sentence of “A detailed description of this algorithm can be found in a previous article [43]” in line 252-253 of original manuscript has been modified to “A detailed description of the principle and main loop of this algorithm can be found in a previous article [49]” in line 296-297, page 9 of revised manuscript. 24.Results & Discussion: In general the results are well related to each phase described in previous section and the discussion highlights the main results and is coherent with them. However, I believe that some minor changes should be made, first of all add the hydrological features of each storm event in Tables. Our respond: Thanks for the reviewer’s suggestion. According to reviewer’s previous suggestion, a new table, Table 1, about hydrological features of selected rainfall events, has been added in line 152, page 5 in the section “2.3. Source of data and model setup” in revised manuscript. This information has not been provided in this section to avoid repetition. 25.Section 3.1: The Observed data (Figure 3) are those relating to the experimental blocks, right? Our respond: Thank the reviewer’s inquiring. Yes, Figure 3 is the comparison of the outflow of experimental blocks of green roof in artificial rainfall experiment with the simulation result of green roof module in SWMM. 26.Table 3: As already said and justified in a previous comment I believe that these two parameters (PFE and VE) are not suitable for evaluating the performance of the model and also the results reported in the Table 3 seem to show my doubt about it. Our respond: Thank reviewer for bring this point to our attention. The parameters of PFE and VE are replaced by PBIAS in Table 4 in line 313, page 10 in revised manuscript. The sentence “PFE ranged from -30.2% to -8.9% and VE ranged from -36.5% to -6.8% for rainfall events in 2014 during the calibration process.” has been modified to “PBIAS ranged from -15.96% to 2.26% for rainfall events in 2014 during the calibration process.” in line 314, page 10 of revised manuscript. The sentence “PFE ranged from -53.8% to -13.2% and VE ranged from -25.6% to -2.3% during the validation process.” has been modified to “PBIAS ranged from -17.97% to -1.95% during the validation process.” in line 316, page 10 of the revised manuscript. 27.It would be more appropriate to assess these parameters in relation to a conventional roof (Normal Roof) as: - Peak Flow Reduction (or hydrograph attenuation), which could be expressed as the percentage difference between the Normal Roof peak flow and the simulated/modelled GR peak flow; - Runoff Attenuation (Volume Reduction) calculated as the absolute percentage difference between the Runoff volume from the Normal Roof and the discharged volume from the modelled/simulated GR. Our respond: Thank reviewer for bring this point to our attention. Table 3 (Table 4 in revised manuscript) shows the evaluation parameter of the simulated and observed outflow of campus drainage network. So, the parameters of Peak Flow Reduction and Runoff Attenuation have not been applied. These two parameters were used when evaluating the effect of roof related LID in Table 4-7. 28.Section 3.2: To better evaluate the hydrological performance of individual LID practices, and comment obtained results (Table 4), it would be appropriate to indicate the Hydrological characteristics of each selected rainfall event: Precipitation Depth, Rainfall Duration and Mean Rainfall Intensity. Our respond: Thanks for the reviewer’s suggestion. According to your previous suggestion, a new table, Table 1, about hydrological features of selected rainfall events providing values of Precipitation Depth, Rainfall Duration and Mean Rainfall Intensity has been added in line 152, page 5, in revised manuscript. These information has not been provided in the section 3.2 to avoid repetition. 29.P11, Line 288: Why the results relating to the scenarios RB-8 and LG-100% are not shown in Table 4? No outflow occur for both scenarios? Anyway, Please add the results of these scenarios, as in the following lines (Lines 296-300) these results continue to be commenting (but not read) Our respond: Thanks the reviewer for bringing it to our attention. Table 4 (Table 5 in revised manuscript) shows the reduction performance of scenarios which had outflow in eight rainfall events in 2014. Scenarios which did not have outflow in eight rainfall events have not be shown in the table to reduce the content of the table. The scenarios of RB-8 and LG-100% did not have outflow for all the rainfall events which has been explained in the in line 327-332, page 11 of revised manuscript. We are afraid that including the performance of all scenarios in eight rainfall events will make the table too long. 30.P11, Line 289-290: Authors claim that "results suggesting that green roofs and greenbelts have a limited ability to cope with heavy events"; I believe that before coming to a conclusion, however not to be excluded, it is necessary consider the hydrological features of each storm event [precipitation depth (PD), rainfall duration (D), rainfall intensity (i)] and the antecedent dry weather period (defined as the dry weather period between two independent rainfall events), which affects the initial soil moisture condition and therefore the soil retention capacity. The same authors, a few lines later (Lines 309-311), claim that the rainfall characteristics affect on performance indicators. Our respond: Thanks the reviewer for bringing it to our attention. Indeed, this expression is not strict. The sentence of “suggesting that green roofs and greenbelts have a limited ability to cope with heavy events” in line 289-290 page 11 of the original manuscript has been deleted in revised manuscript. 31.Table 4, Table 5, Table 6, Table 7 and Table 9: As already said, please add the hydrological features of each storm event. Our respond: Thanks the reviewer for bringing it to our attention. A new table, Table 1, providing hydrological features of each storm event has been added in line 152, page 5 in revised manuscript accordingly and the values of rainfall property has not been provided in Table 4-9 to avoid repetition. 32.Section 3.5: I would add a few more considerations Our respond: Thanks the reviewer for bringing it to our attention. The section related to reduction effect of LID at campus scale is brief due to length limitations. Special research about it may be conducted in our future study. 33.Conclusions P18; Lines 453-454: I believe that the conclusions section is necessary Our respond: Thanks for the reviewer’s suggestion. The sentence of “This section is not mandatory, but can be added to the manuscript if the discussion is unusually long or complex.” in line 453-454, page 18 of original manuscript has been deleted in the revised manuscript.

Reviewer 3 Report

Dear authors, you did a nice research and the results are needed for engineers working in this field. I like your study nevertheless I would give you some remarks to make the paper more interesting/readable

I would recommend to shorten Figure 1, because most of it is obvious.

Please shorten also the description of SWMM (line 115-120) or delete it totally and Focus on LID

Please skip the NSE equations - everyone knows it well

In line 187 you use the abbrevation GB which is not yet defined

Please find another solution for table 2. This Version is too long.

I have also Problems with the length of chapter 3. The results are interesting but it would be better to put it in an appendix and to formulate it shorter. Your conclusions fit better

There is a mistake in line 400. According toi table 8 LG-25% has the lowest cost efficieny not LG-50%.

 

 

Author Response

Response to Reviewer Comments 3#:

Point 1. Moderate English changes required

  Our respond: Thank the reviewer for pointing out it. The article has been checked thoroughly and the following grammar mistake has been revised. “-” has been deleted in the sentence “This study provides an important reference for urban water management and LID-related decision making.” in line 31, page 1 in revised manuscript. A space has been added between “stormwater” in the sentence “LID practice is considered to be a distributed practice that manages stormwater close to the source of runoff generation [8]” in line 42, page 2 of revised manuscript. “methods” has been deleted in the sentence “However, the effect of a combination of LID methods has seldom been evaluated in detail considering the hydrological relationship between composed LID, especially on a larger scale.” in line 70-71 in revised manuscript. “solely” has been added after “were” in the sentence “However, in most previous studies, the parameters of the LID module in SWMM were solely set up based on the suggestions from the model handbook or experience, decreasing confidence in the results.” in line 76, page 2 of revised manuscript. “-” has been deleted in the sentence “This study lays the foundation for LID planning at the building scale and can provide good support for LID-related decision making.” in line 92, page 3 of revised manuscript. “-” has been modified to “to” in the sentence “The campus is flat overall, and its elevation ranges from 47.5-52.9 m.” in line 108, page 3 of revised manuscript. “a” has been added before “height” in the sentence “The parameters of the rain barrel were set based on the real rain barrel used on the campus, with a basal area of 3 m2 and height of 2 m for each barrel.” in line 169, page 5 of revised manuscript. “as” has been modified to “to” in the sentence “The parameters of the low elevation greenbelt were set to be identical to those of the greenbelt except that the berm height was set as 150 mm.” in line 173, page 5 of revised manuscript. The letter H in heigh, T in thickness, C in capacity, P in point, S in slope, H in head and S in saturated has been modified to be lowercase in Table 2 in line 177 of revised manuscript. “were” has been modified to “was” in the sentence “A total of 749 subcatchments were delineated with roofs, greenbelts, roads, sports fields, asphalt pavement and concrete pavement types.” in line 181, page 6 of revised manuscript. “observation” has been modified to “observed” in the sentence “N is the number of observation values. is the mean value of the observed data.” in line 191, page 6 of revised manuscript. “is” has been modified to “was” in the sentence of “The rain barrel scenario means that roof runoff was directed into the rain barrels.” in line 207, page 7 of revised manuscript. “combined” has been modified to “combination” in the sentence “The specific area of each LID application in the combined scenarios was adjusted according to its reduction performance.” in line 218, page 7 of revised manuscript. “related” has been added before “LID” in the sentence of “To explore the effect of roof LID at the campus scale” in line 232, page 7 of revised manuscript. “types of” has been added in the sentence “The effect of LID on runoff reduction is generally reflected by three types of indicators” in line 249, page 8 in revised manuscript. “inside” has been modified to “in” in the sentence “To better quantify the performance of rain barrels at the building scale, effect indicators for rain barrels were calculated inside the time ranges of rainfall events” in line 261, page 8 of revised manuscript. “s” has been added after “equation” in the sentence “Cost-effectiveness was calculated based on the following equation” in line 282, page 9 of revised manuscript. “fr,n” has been modified to “fr,t” In the sentence “fr,n is the present value factor of the discount rate r in year t” in line 286, page 9 of revised manuscript. “is” has been modified to “was” in the sentence of “The US dollar is taken as the unit of cost in this study.” in line 287, page 9 of revised manuscript. “s” has been added after “zero” in the sentence “While the intensity of artificial rainfall was 29 mm/h, the simulated and observed outflows were all zero.” in line 304, page 10 of revised manuscript. “s” has been added after “fit” in the sentence “Figure 3 shows that the simulated hydrological response fit well with the observed values.” in line 304, page 10 of revised manuscript. E in “Rainfall events”, T in “Rainfall type” has been modified to be lowercase in Table 4 in line 313, page 10 of revised manuscript. “scenario” has been deleted in the sentence “Figure 4 shows that in the event of 07-29-2014, only the GR scenario had outflow. ” in line 327, page 11 of revised manuscript. “s” has been added after “event” in Table 5 and Table 6 in line 341, page 11 and line 379, page 13 of revised manuscript. The sentence “Limiting the amount of soil on green roofs and the infiltration rate for greenbelts limit the volume reduction abilities of these two practices.” has been modified to “The limited amount of soil in green roofs and the restricted infiltration rate for greenbelts constrain the volume reduction abilities of these two practices.” in line 346-348,page 12. “combined” has been modified to “combination” in the sentence “There was no outflow in the other rainfall events for all combined scenarios.” in line 372, page 12 of revised manuscript. “combined” has been modified to “combination” in the sentence “Figure 5 shows that the combined scenarios can effectively control all rainfall events with fewer areas of composed LID.” in line 375, page 13 of revised manuscript. “for” has been modified to “in” in the sentence “For the storm event of 09-02-2014, only GR&RB had outflow.” and “For the storm event of 08-31-2014, all combined scenarios had outflow. ” in line 376-377, page 13 of revised manuscript. “combined” has been modified to “combination” in the sentence “In the storm event of 08-31-2014, all combined scenarios had outflow.” in line 377, page 13 of revised manuscript. “combined” has been modified to “combination” in the sentence “The performances of the combined scenarios are summarized in Table 6.” in line 378, page 13 of revised manuscript. “combined” has been modified to “combination” in the sentence “Based on the volume reduction amount in the event of 08-31-2014, the ranking of the combined scenarios is GR&RB&LG > RB&LG > GR&LG > GR&RB.” in line 389, page 13 of revised manuscript. “as” has been modified to “to” in the sentence “The unit construction cost and percent of cost for unit operation and maintenance were set as 280-340 dollars/m2 and 1%, respectively [54].” in line 443, page 16 of revised manuscript. “as” has been modified to “to” in the sentence “The service life of all LID practices was set as 20 years [48, 54]” in line 444, page 16 of revised manuscript. “scenario” has been deleted in the sentence “Table 9 shows that the LG-25% scenario has the highest cost efficiency, while GR has the lowest cost efficiency.” in line 448, page 17 in revised manuscript. “for” has been modified to “of” in the sentence “In addition, a minimum area for green fields is required by the Chinese government.” in line 454, page 17 of revised manuscript. “on” has been modified to “at” in the sentence “3.5 Reduction effect on campus scale” in line 485, page 18 of revised manuscript. “could have” has been deleted in the sentence “It can be seen in Table 10 that individual and combined LID practices implemented to reduce roof runoff could have effectively reduced the outflow and overflow of the campus in 2017.” in line 490, page 19 of revised manuscript. “the” has been added before “minimal” in the sentence “Scenarios with rain barrels have minimal volume reduction ability because they store runoff during rainfall events and discharge all the water after.” in line 492, page 19 of revised manuscript. “RB-8 (LG-100%)” has been modified to “LG-100%>RB-8” In the sentence “The ranking of individual LID scenarios based on their volume reduction amount in the rainfall event of 08-31-2014 and precipitation with a 50-year return period is RB-8 (LG-100%) > LG-50% > RB-4 > GR > GB.” in line 514, page 19 in revised manuscript. “Normal” has been added after “Beijng” in the sentence “X.H. developed the campus model of Beijing Normal university” in line 539, page 20 in Author Contributions section of revised manuscript. “Cities-Contruction” has been modified to “Cities-Construction” in the reference name of “Technical Guide for Sponge Cities-Construction of Low Impact Development” line 567, page 20 in revised manuscript.

Point 2. I would recommend to shorten Figure 1, because most of it is obvious.

Our respond: Thanks for the reviewer’s suggestion. Figure 1 has been shorten in line 98, page 3 in revised manuscript. The rectangles of “Calibration and validation”, “Parameter adjustment” and “Typical roof selection” in Figure 1 in original manuscript have been deleted. The texts of “Observation data at outfall” has been modified to “Observed hydrological data at outfall of campus in 2014” to make it more specific. The text of “Established SWMM model of Beijing Normal university” has been modified to “SWMM model of Beijing Normal university”. The text of “LID scenarios setup” has been modified to “Scenarios setup”. the text of “Cost-effectiveness analysis of LID scenarios” has been modified to “Cost-effectiveness analysis”. The text of “LID combination optimization” has been modified to “Combination optimization” in the revised manuscript to make the figure briefer.

Point 3. Please shorten also the description of SWMM (line 115-120) or delete it totally and Focus on LID

Our respond: Thanks for the reviewer’s suggestion. The sentence “It is composed of four functional blocks, i.e., runoff, transport, extran and storage and treatment, plus an executive block [25]. It is a semi-distributed model” before the sentence “and has been widely applied in thousands of studies to simulate hydrology” in line 116-118 page 4 of original manuscript has been deleted. “and” has been modified to “It” in the sentence “and has been widely applied in thousands of studies to simulate hydrology” in line 124, page 4 in revised manuscript. The sentence “A detailed simulation equation for each block can be found in previous papers [25,29].” after the sentence "the water quality of urban storm runoff and the effect of mitigation practices in urban watersheds [26-28]" in line 120 page 4, of original manuscript has also been deleted. Only a brief introduction of SWMM was retained in line 123-126, page 4 of revised manuscript. Attached please find the revised manuscript.

Point 4. Please skip the NSE equations - everyone knows it well

Our respond: Thank reviewer for bringing this point to our attention. Equation (1) of NSE has been deleted in line 189 page 6 of revised manuscript. The numver of other equations has been revised accordingly. Attached please find the revised manuscript.

Point 5. In line 187 you use the abbrevation GB which is not yet defined

Our respond: Thank reviewer for bringing this point to our attention. The definition of “GB” has been added in the sentence “The scenario of greenbelt (GB) was set such that roof runoff was directed into the greenbelt behind the building.” in line 200-201, page 6, in revised manuscript according to your suggestion.

Point 6. Please find another solution for table 2. This Version is too long.

Our respond: Thanks for the reviewer’s suggestion. The lines of “Scenarios” and “Explanation” in Table 2 of original manuscript (Table 3 in revised manuscript) have been deleted in Table 3 in line 246, page 7 of revised manuscript to make the table shorter and briefer. “Abbreviation” in Table 2 of original manuscript has been modified to “Scenarios” in Table 3 of revised manuscript. The deleted content has been transferred to main text and rewrote as “The scenarios of green roof (GR) was set that green roof covered all roof area of 4th teaching building.” in line 199-200, page 6, “Three low elevation greenbelt scenarios (LG) were set, i.e., the scenario setting the area of low elevation greenbelt to 25% of the area of 4th teaching building (LG-25%), the scenario setting the area of low elevation greenbelt to 50% of the building roof (LG-50%) and the scenario setting the area of low elevation greenbelt to the same as building roof (LG-100%) to detailed simulate the performance of low elevation greenbelt.” line 210-215, page 7, “The scenario of combined green roof and rain barrel (GR&RB) means that the outflow of 260 m2 green roof and 260 m2 normal roof was directed into two rain barrels. The scenario of combined green roof and low elevation greenbelt (GR&LG) represents that the outflow of 260 m2 green roof and 260 m2 normal roof was directed into low elevation greenbelt of 130 m2. The scenario of combined rain barrel and low elevation greenbelt (RB&LG) represents that roof runoff was directed into two rain barrels and then into low elevation greenbelt of 130 m2. The scenario of combined green roof, rain barrel and low elevation greenbelt (GR&RB&LG) represents that outflow of 520 m2 green roof was directed into two rain barrels and then into low elevation greenbelt of 130 m2. The scenario of combined 100% of Green roof, eight rain barrels and 100% of low elevation greenbelt (GR100%&RB&LG100%) means that outflow of 520 m2 green roof was directed into eight rain barrels and then low elevation greenbelt of 520 m2.” in line 219-230, page 7, “GR means that all flat roofs in BNU were covered with green roofs. GB means that roof runoff was directed into adjoining greenbelts. RB-4 and RB-8 mean that roof runoff was directed into four rain barrels and eight rain barrels, respectively, for each roof.” in line 235-238, page 7 and “The scenario of combined green roof, rain barrel and greenbelt (GR&RB&GB) represents that the outflow of green roof was directed into four rain barrels and then into the adjoining greenbelt for each roof. GR&RB&LG at campus scale means that the outflow of green roof was directed into four rain barrels and then into the adjoining low elevation greenbelt for each roof.” in line 240-244, page 7 in revised manuscript. The sentence “The NR scenario was set as the base scenario to calculate the reduction indicator of other scenarios.” has been modified to “The scenario of normal roof (NR) represents the 4th teaching building without any LID, which was set as the base scenario to calculate the reduction indicator of other scenarios.” and been moved after the sentence of “At the building scale, thirteen scenarios were developed: seven for individual LID practices, five for combined LID practices and one for the base scenario.” In line 197-199, page 6 of revised manuscript. The sentence “The GB scenario was set such that roof runoff was directed into the greenbelt behind the building.” has been modified to “The scenario of greenbelt (GB) was set such that roof runoff was directed into the greenbelt behind the building.” in line 200-201, page 6 of revised manuscript. “(RB)” has been added in the sentence of “The rain barrel scenario (RB) means that roof runoff was directed into the rain barrels.” in line 207 page 7 in revised manuscript. The sentence of “As there are eight downspouts for the building, two rain barrel scenarios were established: the four rain barrel scenario and the eight rain barrel scenario.” has been modified to “As there are eight downspouts for the building, two RBs were established: the four rain barrels scenario (RB-4), directing roof runoff into four rain barrels, and the eight rain barrels scenario (RB-8), directing roof runoff into eight rain barrels.” in line 208-210, page 7 in revised manuscript. “in previous papers” has been deleted in the sentence of “Combination scenarios were set with less area for composed LID based on the commonly used method of setting combined LID scenarios in previous papers [11].” in line 217, page 7 of revised manuscript. The sentence “The detailed content of these scenarios is shown in Table 2.” has been modified to “The areas covered by LID scenarios are shown in Table 3.” in line 230, page 7 of revised manuscript. The sentence “NR was taken as the base scenario.” has been modified to “NR at campus scale, which was taken as the base scenario, represents that the outflow of roofs in BNU was directed directly into the nearby sewer inlets.” and moved to be after the sentence of “To explore the effect of roof related LID at the campus scale, eight scenarios, five for individual LID practices, two for combined LID practices and one base scenario, were set up for the BNU roofs.” in line 234-235 page 7 in revised manuscript. The sentence “Greenbelts were retrofitted to low elevation greenbelts to receive runoff from adjoining roof to enact the LG scenario.” has been modified to “Greenbelts in BNU were retrofitted to low elevation greenbelts to receive runoff from the adjoining roofs to enact the low elevation greenbelt scenario (LG).” transferred before the sentence “The areas covered by LID scenarios can also be seen in Table 3” in line 238-239 in page 7 in revised manuscript. The sentence “Detailed scenario settings can be seen in Table 2.” has been modified to “The areas covered by LID scenarios on the campus can also be seen in Table 3 and Figure S1 in supplemental material.” in line 244-245, page 7 in revised manuscript.

Point 7. I have also Problems with the length of chapter 3. The results are interesting but it would be better to put it in an appendix and to formulate it shorter. Your conclusions fit better.

Our respond: Thanks for the reviewer’s suggestion. We also feel that chapter 3 is a little long. However, every composed part in this section is important to support the conclusion. We think that maybe it is better keep it in main text to facilitate reading. To make this section shorter, “such as the availability of neighboring green land and the load bearing of roofs” has been deleted in the sentence “The selection of applied LID should be based on objective and local conditions such as the availability of neighboring green land and the load bearing of roofs.” in line 368-369, page 12 of revised manuscript. The sentence “With the increase in the return period, the volume reduction amounts of GR increased slightly, while the peak reduction rates and volume reduction rates had decreasing trends. The volume reduction amounts of GB and RB decreased slightly, while their peak reduction rates and volume reduction rates had the same trends as the green roofs.” in line 357-360, page 14 of original manuscript has been deleted . The sentence “Compared to the volume reduction rate and the peak reduction rate, the indicator of the volume reduction amount changes little for different return periods.” has been modified to “With the increase in the return period, the volume reduction rate and the peak reduction rate decrease obviously,while the volume reduction amount changes little” in line 411-413, page 15 of revised manuscript. The sentence “For 10 years of precipitation, the variation trends in the volume reduction amount, volume reduction rate and peak reduction rate are the same.” in line 388-389, page 16 in original manuscript has been deleted.

Point 8. There is a mistake in line 400. According to table 8 LG-25% has the lowest cost efficieny not LG-50%.

Our respond: We overlooked this in the original version of our manuscript and thank the reviewer for bringing these points to our attention. "LG-50%" has been revised to “LG-25%” in line 448, page 17 in revised manuscript. Attached please find the revised manuscript.

Round 2

Reviewer 3 Report

Dear authors, you improved your manuscripz a lot. Congratulations