Urban Water Security Assessment Using an Integrated Metabolism Approach—Case Study of the National Capital Territory of Delhi in India
Round 1
Reviewer 1 Report
The manuscript presents an application of a given methodology to the National Territory of Delhi. It presents a water balance using the concepts of a metobolic approach. It is not clear what is the added value of this approach, when compared to a standard water balance.The text needs some improvement to increase its readability, as the authors assume the reader is familiar with very specific concepts and many acronyms. Some examples are presented below
Abstract ; line 45- metabolic flows
p.1; line 65 - MFA
p.5 ; line 30 - "The stocks of water ....." - please provide an hydrological explanation
p.6; line 153 and line 156 - Cropping intensity and its value (148%)
p.7; line 187 - "inflow from stock" - please provide an hydrological explanation
Section 2.1 - The presentation of water availability in Delhi is confusing. The water sources referred in the text do not match the ones on Table 1. The net water availability referred in the text (0.29 BCM) cannot be inferred from Table 1. In addition, what does Bhakra storage mean?
p.8 /p.9 - The discussion on water needs and water demand is confusing. The total of Table 3 is 1017.6 MCM but the text refers that the annual demand is 694.7 MCM.
Overall, all figures need to be redesigned as they are very hard to read.
Table 4 needs a source or an explanation on how the figures were computed.
Author Response
Responses to comments from Reviewer 3
Comments and Suggestions for Authors
The manuscript presents an application of a given methodology to the National Territory of Delhi. It presents a water balance using the concepts of a metobolic approach. It is not clear why this water balance
The introduction section now has more information about this…and that should make things clearer to readers.
The text needs some improvement to increase its readability, as the authors assume the reader is familiar with very specific concepts and many acronyms. Some examples are presented below
Abstract ; line 45- metabolic flows
‘Metabolic flows’ is a common term from Urban metabolism literature which considers resource flows in and out of cities as might for an organism. We have now added on a new reference to this, in case readers wish to know more about the origin of this term. (Ref: WOLMAN, A. 1965. The Metabolism of Cities. Scientific American, 213, 179-190.
p.1; line 65 – MFA
This has now been taken care of in the revised version.
p.5 ; line 30 - "The stocks of water ....." - please provide an hydrological explanation
“The stock of water ..” is water available within city boundary and in this case includes ground water and open water bodies/ponds’. This now has been added on to the text.
p.6; line 153 and line 156 - Cropping intensity and its value (148%)
This is a well known term - Cropping intensity = (Gross cropped area / Net sown area) x 100. Now, added on in the text, at the relevant juncture.
p.7; line 187 - "inflow from stock" - please provide an hydrological explanation
As explained earlier, it is amount of water taken from stock i.e. ground water and open water bodies/ponds
Section 2.1 - The presentation of water availability in Delhi is confusing. The water sources referred in the text do not match the ones on Table 1. The net water availability referred in the text (0.29 BCM) cannot be inferred from Table 1. In addition, what does Bhakra storage mean?
Rewriting has now been done, and Bhakra Storage has been explained in the text.
p.8 /p.9 - The discussion on water needs and water demand is confusing. The total of Table 3 is 1017.6 MCM but the text refers that the annual demand is 694.7 MCM.
It is already stated in the text that 694.7MCM includes 15% losses and excludes demand by TPPs and Agriculture
Overall, all figures need to be redesigned as they are very hard to read.
We have tried to improve the quality of some of them, to the best of our abilities.
Table 4 needs a source or an explanation on how the figures were computed.
The table has been constructed on the basis of the analysis done in this paper..explained in the Methodology section clearly
Reviewer 2 Report
The authors proposed an integrated metabolism approach to estimate the urban water security. The National Capital Territory of Delhi in India was selected as the case-study city. Some relevant hydrological performance indicators were used to analyze urban water infrastructure.
However, Urban water metabolism system is simplified, the majority of the outcomes are quite obvious, thus not very interesting for a reader. Apart from this main drawback, which should require an extremely deep revision of the manuscript, there are other main issues that the authors surely must resolve before the manuscript can be suitable for publication:
1. How to consider the uncertainty of inflow and outflow?
2. Do the authors ever think about accuracy evaluation of urban hydrological performance indicators? Could you make the error analysis of the water balance?
3. Abstract: “and the annual groundwater withdrawal, which exceeds 420 million cubic metres, is much greater than the recharge rate, resulting in a rapid depletion of the groundwater level.” The conclusions are obvious. Could you have any other innovation point?
4. “4. Conclusions and recommendations”: The discussion is mixed with the conclusion. Can you separate that?
5. What the authors are trying to achieve, and finally what are the primary results to be beneficial for urban water security? It is not clear from the conclusions.
Comments for author File: 
Comments.docx
Author Response
The authors proposed an integrated metabolism approach to estimate the urban water security. The National Capital Territory of Delhi in India was selected as the case-study city. Some relevant hydrological performance indicators were used to analyze urban water infrastructure.
However, Urban water metabolism system is simplified, the majority of the outcomes are quite obvious, thus not very interesting for a reader. Apart from this main drawback, which should require an extremely deep revision of the manuscript, there are other main issues that the authors surely must resolve before the manuscript can be suitable for publication:
1. How to consider the uncertainty of inflow and outflow? Do the authors ever think about accuracy evaluation of urban hydrological performance indicators? Could you make the error analysis of the water balance?
Permit us to club together the first two questions and answer them together. Getting data from a developing country like India (where there is reluctance on the part of data owners and relatively little cooperation with researchers, vis-à-vis European settings), is a tough challenge, which we have tried to overcome by thinking laterally. Most of the data we have used are long-term averages (50-year averages for river flow and rainfall). Some data elements are extrapolated from the data, which were accessible to us. We must point out here that data that are accessible are also not peer-reviewed. And the main objective of this article (which is the first type of analysis done for Delhi), is to present a macro-view of the situation. Hence, we would like to believe that uncertainty analysis is not really relevant in this case.
Further, when you refer to accuracy of indicators, there is a strong link to the explanation regarding the input data given in the earlier paragraph. The indicators are our model’s outputs and are of course sensitive to the time-averaged or extrapolated data inputs which the model has received.
2. Abstract: “and the annual groundwater withdrawal, which exceeds 420 million cubic metres, is much greater than the recharge rate, resulting in a rapid depletion of the groundwater level.” The conclusions are obvious. Could you have any other innovation point?
Well, we have followed this up now, in the Abstract by stating that this makes an increase in the infiltration rate of stormwater extremely important, by attempting to increase the fraction of surfaces with higher permeability to rainwater in the city.
3. Conclusions and recommendations”: The discussion is mixed with the conclusion. Can you separate that?
Thanks for pointing this out. It has been done, in the revised version and marked in the manuscript.
5. What the authors are trying to achieve, and finally what are the primary results to be beneficial for urban water security? It is not clear from the conclusions.
2-3 sentences have now been added on to the truncated Conclusions section, which focus on the ‘must-do’s to ensure water security in a water-stressed mega-city like Delhi.
Thanks for the annotated comments on the PDF…we have also addressed them in the revised version.
Author Response File: Author Response.docx
Reviewer 3 Report
The authors carry out a water balance of the Indian megacity of Delhi using hydrological performance indicators. The paper has some merits, but the authors failed in demonstrating ist novelty and mainly its scientific significance. In the present form the paper seems to be a technical report. Moreover, some details lack in the Methods section, the abstract must be thoroughly rewritten and discussions enriched with comparison with relevant literature. Some minor concerns are reported in the attached file.
Comments for author File: 
Comments.pdf
Author Response
The authors carry out a water balance of the Indian megacity of Delhi using hydrological performance indicators. The paper has some merits, but the authors failed in demonstrating its novelty and mainly its scientific significance.
Thanks for the comment. In our opinion, the paper is intended to be a decision-support aid, which prompts, motivates and urges action at the policy-making level. This special issue is oriented towards policy-making and the role of analytical studies as decision-support aids for the same. In keeping with the title of the main journal of which this particular one is a special issue, the focus is on water as a resource, and the much-needed change in perspective regarding what constitutes a resource.
In the present form the paper seems to be a technical report.
We would politely like to disagree. The paper has presented a concise, reproducible methodology which can be extended to other cities within India, and beyond, and derive comparative indices.
Moreover, some details lack in the Methods section
In the Methods section, we have outlined all the equations, which have been used and also identified all the data sources, which in our opinion, make for a clear and logical two-part methodology comprising of data gathering and application of data to calculate indices which can then be utilised in communications with decision-makers at the city-government level.
The abstract must be thoroughly rewritten
In the changed version, some changes have been made to the Abstract and these have been identified with yellow-marking
Discussions enriched with comparison with relevant literature.
We had introduced a couple of references from literature to a Portuguese and an Israelite case study to reinforce the need for looking at wastewater as a resource in India.
Some minor concerns are reported in the attached file.
The file we received was a different paper…which seemed to be a published one, with annotations…
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The manuscripts uses a set of indicators without any presenting any sound reference values. At times, the values computed for Delhi are compared with values from other cities, selected without any justification, which renders the comparison meaningless.
The whole city water balance is presented in a confusing way, which makes the manuscript rather hard to read. A clear picture of the water flows should help in understanding the authors argument.
At times, the authors analysis seem to be based on two debatable assumptions: i) that unused water flowing into the city is a waste - what about ecological needs?; ii) the city water supply must be sustained from the rain falling within the city limits - large cities draw water from outside sources.
Additionally, the following comments should help in improving the manuscript
p.2, line 49/50 - Still not clear why the urban water metabolism approach provides better insights than a conventional water balance approach.
p.2, line 83/83 - The Bhakra-Nadal dam is built on which water course? Does this water course go through the city?
Fig. 1 should include a map with the main water courses and water sources.
Fig. 1 b and c should be merged.
p.5, line 95 - How does loss reduction become an additional water source?
p.5 line 110 - Why is Ganga flow not considered in unutilized flow?
p.5 line 110 - Are leakages from pipelines considered as groundwater recharge?
p.6, line 144 - Improve crop intensity definition and explanation
p.7, line 174 - Water demand is not included in the WUI definition
p.9, line 238 - State domestic water demand as MCM to facilitate comparisons with Table 2
p.12, line 339 - Why use Australian cities as a standard?
p.13, line 345 - A low SC value indicates the existence of a private market or the use of individual sources. One cannot conclude a lack of regulatory control over private abstraction.
p.13, lines 350-359 - River Ganga is absent from this analysis
Author Response
We thank the reviewer for useful suggestions to enhance our paper. We have incorporated the suggestions in the revised manuscript to the extent possible. For some others, we have given explanation in this sheet for the consideration of the reviewer.
Comments and Suggestions for Authors
Comment 1. The manuscripts uses a set of indicators without any presenting any sound reference values. At times, the values computed for Delhi are compared with values from other cities, selected without any justification, which renders the comparison meaningless.
Response: Reference values of indicators is not required since each city has water flows unique to its characteristics. We have illustrated a methodology and use of indicators that may help urban planners to understand such flows and draw meaningful information for water planning and policy. Several such studies for other cities, once carried out, may provide information for intercity comparison.
Except for WUI indicator (lines 347-348), which is compared with Australian cities, at no other place any Indicator value is compared with any other city in the paper. Only some examples have been given for other cities to strengthen an argument (like in line numbers 394-397), which were added on suggestions of an earlier reviewer during first round of review of this paper. WUI was compared with Australian city to inform that the value is dependent on choice of system boundary (inclusion/exclusion of urban agriculture as explained in line numbers 349-351), which we feel is useful.
Comment 2. The whole city water balance is presented in a confusing way, which makes the manuscript rather hard to read. A clear picture of the water flows should help in understanding the authors argument.
Response: We have reworked on sections 3.2, 3.3 and Figure 3. We have replaced approximate values with exact values so that values in figure is similar to the text, redundant and repeated information have been removed. We have also rechecked all values and corresponding explanation in text from section 3.1 to 3.3.With these revisions we assess that it will be easier for a reader to comprehend.
Comment 3. At times, the authors analysis seem to be based on two debatable assumptions: i) that unused water flowing into the city is a waste - what about ecological needs?; ii) the city water supply must be sustained from the rain falling within the city limits - large cities draw water from outside sources.
Response: (i) A significant amount of unused water is in the form of runoffs due to high intensity rainfall. The number of rainy days in Delhi are less than 40 a year, majorly confined during the month July-Sep. Historically the river Yamuna in other months of the year is recharged through ground water flows. Therefore, at present the runoff water do not contribute to ecological flows, but a reason of increased frequency of flooding in the region. Water storage structure and revival of urban water bodies to tap this runoff would improve both water security, groundwater recharge and ecological flows.
(ii) In lines 358 to 367 we argued that under ideal condition, rainfall can at best meet only 65% of water needs. Hence, utilisation of wastewater coupled with reduction in losses is the way forward. Delhi is not likely to get more water from other regions and the current level of imported water flows in Delhi will remain stressed with negative bias.
Additionally, the following comments should help in improving the manuscript
Comment: p.2, line 49/50 - Still not clear why the urban water metabolism approach provides better insights than a conventional water balance approach.
Response: We have further explained in the revised manuscript to address the observation of the reviewer.
Comment: p.2, line 83/83 - The Bhakra-Nadal dam is built on which water course? Does this water course go through the city?
Response: It’s on Sutlej river. We have mentioned in the revised manuscript and have also added references for all data in Section 1.1 (lines 83-109). For the ready reference of the reviewer, please see page 189 of the following link.
http://delhi.gov.in/wps/wcm/connect/16541d8048d8ebdea8e9f97a2b587979/ESD+2014-15+-+Ch-13.pdf?MOD=AJPERES&lmod=519320373&CACHEID=16541d8048d8ebdea8e9f97a2b587979
Comment: Fig. 1 should include a map with the main water courses and water sources. Fig. 1 b and c should be merged.
Response: Suggestions addressed in the revised manuscript.
Comment: p.5, line 95 - How does loss reduction become an additional water source?
Response: This information is taken from information published by the concerned government agency. We have added references in the revised manuscript.
Comment: p.5 line 110 - Why is Ganga flow not considered in unutilized flow?
Response: Ganga do not flow in Delhi but its water reaches Delhi through canals as explained in section 1.1. Flow in canals is regulated and distributed by irrigation department. Only the river Yamuna flow through Delhi.
Comment: p.5 line 110 - Are leakages from pipelines considered as groundwater recharge?
Response: Leakages contributes to unutilized flow (Wu), part of which is recharges GW, part into storm water and goes to WWTP, and remaining flow through or evaporate.
Comment: p.6, line 144 - Improve crop intensity definition and explanation
Response: We have further defined it in the revised manuscript.
Comment: p.7, line 174 - Water demand is not included in the WUI definition
Response: In our paper we have highlighted distinction between water demand (estimated based on normative values) and the water supply. WUI is based on actual water supply. This has been explained in Lines 182-184.
Comment: p.9, line 238 - State domestic water demand as MCM to facilitate comparisons with Table 2
Response: We have done in the revised manuscript.
Comment: p.12, line 339 - Why use Australian cities as a standard?
Response: It is not chosen as a standard, but the value is available in the literature for these cities using the method. WUI was compared with other cities to inform that the value of WUI is dependent on choice of system boundary (inclusion/exclusion of urban agriculture)
Comment: p.13, line 345 - A low SC value indicates the existence of a private market or the use of individual sources. One cannot conclude a lack of regulatory control over private abstraction.
Response: We agree with the reviewer that lower value of SC by itself do not indicate ‘lack of regulatory control over private abstraction’. We have removed this phrase. However, lower value of SC do indicate possibility of presence of private abstraction since government supplies are centralized.
Comment: p.13, lines 350-359 - River Ganga is absent from this analysis
Response: As explained earlier, river Ganga do not flow in Delhi. Its water is supplied to Delhi through canals regulated by irrigation department.
Author Response File: Author Response.docx
Reviewer 2 Report
Paper has been revised adequately, hence it's now in an acceptable stage.
Author Response
Comments and Suggestions for Authors
Comment: Paper has been revised adequately, hence it's now in an acceptable stage.
Response: We thank the reviewer for his positive consideration.
Reviewer 3 Report
The authors have carried out limited work to modify the paper, but something has been improved. Mainly the discussions need to be enlarged (adding 2 references is too little) with sentences with comparisons. I apologise for sending the wrong commented paper, after realising it, I have sent to the editor the right paper. Thus I invite the authors, if they agree, to consider also the suggestions given.
Author Response
Comments and Suggestions for Authors
Comment: The authors have carried out limited work to modify the paper, but something has been improved. Mainly the discussions need to be enlarged (adding 2 references is too little) with sentences with comparisons. I apologise for sending the wrong commented paper, after realising it, I have sent to the editor the right paper. Thus I invite the authors, if they agree, to consider also the suggestions given.
Response:
Other than 6 new references for data in section 1.1, following more references have been included
Ramos, G. C. D., (2015) Water and Political ecology of urban metabolism: the case of Mexico city. Journal of Political Ecology, 22, 98-114.
Musango, J.K., Currie, P. & Robinson, B. (2017) Urban metabolism for resourceefficient cities: from theory to implementation. 40p. Paris: UN Environment. 40p
Angelakis, A. N., and Synder, S. A. (2015) Wastewater Treament and Resuse: Past, present, and Future. Water (7): 4887-4895.
