Evaluating the Risk-Based Performance of Bioinfiltration Facilities under Climate Change Scenarios
Round 1
Reviewer 1 Report
A beautifully written manuscript. Should be ready to accept after attending the minor comment below and a quick check for typographic mistakes.
Comment:
Page 5, Lines 189-194: it is not very clear which of these figures belong to baseline and the two RCP scenarios. Seems a bit mixed up.
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
This paper presents an evaluation of the performance of bioinfiltration facilities (BI) under several climate change scenarios. The evaluation is performed following a „risk-based“ methodology that the authors have recently published, and two well-known hydrologic—hydraulic models. My biggest concern is that the main aspects of this study have already been published (Lewellyn and Wadzuk, 2018) – the risk-based methodology and the performance of the treatment train at the Villanova University. The only new results are those dealing with future projections for the impact of climate change on increase in temperature and precipitation and consequently the performance of BI. Although, those results are interesting, they are more appropriate for a technical report than a scientific journal.
In addition, I have some specific comments regarding the manuscript text, methodology and results.
1. The introduction provides only the motivation for this study, but is missing an overview of similar studies. Are there other similar methodologies used to evaluate the performance of BI? Are there other studies evaluating the climate change impacts on the performance of BI? Why is this study important? What is new proposed here that can be applied in other studies? These questions should be answered and highlighted in the Introduction.
2. Although the “risk-based” methodology has been published and therefore should not be questioned here, I still have some issues that must be, at least, explained better. I am aware that “risk” has many different definitions, but almost all of them define it as some combination of hazard, exposure and vulnerability, where hazard includes the probability of occurrence of some event (for example, see IPCC). Additionally, the risk is usually expressed as an index, or a scale, or a level, etc. However, in this study it is expressed as a physical unit (mm/yr) which I find confusing and not consistent with other studies in this field. I find that the computed values actually represent hazard, and not risk. This requires a better explanation. Furthermore, rainfall volume is expressed in (mm)?? This is not physically corrected, either express “volume” in (m3) or (L), or rename the parameter to rainfall height/depth.
3. Climate change modelling should better explain the relation between annual values and individual events. Only the changes in annual values are presented (Page 5, Lines 183-194). Changes in individual events are only discussed by mentioning the results from other studies. Since a series of individual events are considered in hydrological modelling, they should be presented more clearly.
4. Before estimating the “risk” of BI overflow, you should first identify what rainfall conditions lead to the overflow (in relation to the ponding depth and hydraulic conductivity).
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
The authors introduce a method of estimating risks of introducing GI (for this case, bioinfiltration) brought about by climate induced changes in precipitation and temperature. Although the work presents a workflow which can be easily implemented. There are multiple areas in the manuscript which require more information. More importantly, an essential issue is that the research problem is not obvious. This lack in a clear problem statement (or detailed introduction) makes it difficult to judge for originaility (i.e. Is the work simply a case study for Philadelphia, Pennsylvania? or for GI in general?). Below are general questions which can hopefully aid the authors in improving their manuscript.
1. The research problem are not clearly stated. What led to the research objectives (L144) of focusing on bio-infiltration and other other GIs? Is the problem about the fact that GI designs do not undergo risk-based approaches (L66-67)? Has this been done previously? If not, what could be the reason for the lack in risk-assessments of GI? or is this mainly about to investigate impacts of climate change induced precipitations to different bioinfiltration designs?
2. Why was Philadelphia, Pennsylvania selected a study site and worthy of investigation? Is this representative of most US cities? This inquiry is in line with the lack in objective statement.
3. If the work is meant to provide detailed methodology to bio-infiltration (or GI) designers, detailed descriptions are necessary. For example, in L145 - 146, discuss in detail the equations used for calculating P_over,v and V_avg,v. Which hydrologic modeling was used?
4. Citation is needed for the declarative statement in L69-70.
5. The climate change inputs are critical to the results. It is necessary to explain via a summary which models were selected for the ensemble dataset prepared in (Reclamation, 2014).
6. In L118 to L122, which method was used for the adjustment?
7. In L123, how was the PET calculated from the mean, minimum, and maximum monthly daily tempearture measurements? Which equation?
8. In L153, what is the basis for selecting the spatial dimensions of the drainage area? Why 930 sq.m. drainage area?
9. It might be helpful to understand the research methodology in detail if a flowchart were added.
10. What is the physical meaning of "development" in "Predevelopment" condition (L147)? Is this the absence of anthropogenic activities or infrastructures?
11. L171 add citations for EPA SWMM
12. The authors inclusion of "Uncertainty" is highly appreciated but it might be possible to include them as latter paragraphs of the conlusion section. The second paragraph of "Uncertainty" addresses the possibly of applying them to other cities, thus, the heading for "Uncertainty" might not be appropriate. This section sounds more like a closing remark.
Author Response
Please see attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authors have corrected or provided an adequate explanation for most of my concerns. The introduction is improved and extended, and the aim is now much clearer. My only issue regarding the definition of the risk remains, but I agree that there does not exist a commonly accepted definition, especially for LID infrastructure. Therefore, since the paper is now improved, and I am satisfied with its current form, I can recommend it for publication.
