Quantifying the UDS Hydraulic and Social Resilience to Flooding: An Index-Based Approach vs. a Parameter-Based MCDM Method

Round 1

Reviewer 1 Report

The manuscript introduces new metrics to evaluate the components of resilience for urban drainge systems namely flexibility and resilience for both hydraulic and social aspects. The method is applied to a part of the urban area of Tehran and compares different retrofitting strategies. In my opinion there are several points to be addressed before publication:

1) From a methodological point of view the application misses a real applicability. I'm pretty sure that increasing the UDS capacity improves the hydraulic robustness as well as using diversion channels, so I'm not surprised that the indices improve in project states. But what are the tradeoff ? Are the solutions assumed feasible, economically and environmentally sustainable? Is there a cost-benefit analysis which identified the best compromise between increasing resilience and investments based on the probability of occurrence of rainfall events and impacts? I think this aspect deserves more attention and references to cost-benefit analysis for flood risk mitigation (also in the conclusions, where limitations should be discussed).

2) the results. It is a pity that the majority of results lies in the supplementary material, while there are some figures, e.g. Fig. 3 that in the present state have a limited meaning. (Fig. 3 hasn't legend, scale, geographical setting of the study are in the Country etc...). A selection of the results should be presented in the main text.

3) The conclusions do not discuss the results obtained with respect to other examples in literature which evaluate resilience with different approaches. E.g. just to cite a few:

Zhu et al. 2021. Enhancing urban flood resilience: A holistic framework incorporating historic worst flood to Yangtze River Delta, China.

Arrighi et al. 2022. Resilience of art cities to flood risk: A quantitative model based on depth-idleness correlation.

Bukvic et al., 2021. Exploring neighborhood-level resilience to flooding: Why the context and scale matter

4) the schemes of Fig. 1 and 4 have a poor resolution. In particular in Fig. 1 check also the consistencies of the terms used in the method section.

Author Response

Response to the Reviews’ Comments

The manuscript introduces new metrics to evaluate the components of resilience for urban drainage systems namely flexibility and resilience for both hydraulic and social aspects. The method is applied to a part of the urban area of Tehran and compares different retrofitting strategies. In my opinion there are several points to be addressed before publication:

• From a methodological point of view the application misses a real applicability. I'm pretty sure that increasing the UDS capacity improves the hydraulic robustness as well as using diversion channels, so I'm not surprised that the indices improve in project states. But what are the tradeoff? Are the solutions assumed feasible, economically and environmentally sustainable? Is there a cost-benefit analysis which identified the best compromise between increasing resilience and investments based on the probability of occurrence of rainfall events and impacts? I think this aspect deserves more attention and references to cost-benefit analysis for flood risk mitigation (also in the conclusions, where limitations should be discussed).

Response 1: You are right. However, this issue is not within the scope of this paper as this study is focusing on “quantifying the resilience and flexibility” of the stormwater drainage infrastructure and their subsets. Therefore, we added the relative explanations in the conclusion section as a limitation for this work (as you suggested).

• The results. It is a pity that the majority of results lies in the supplementary material, while there are some figures, e.g. Fig. 3 that in the present state have a limited meaning. (Fig. 3 hasn't legend, scale, geographical setting of the study are in the Country etc...). A selection of the results should be presented in the main text.

Response 2: According to your suggestion, a selection of the results were included in the manuscript.

Regarding Figure 3, the objective is to, just, illustrate the situation of the studied catchment in the whole province and the country. That’s why no more geographic information is provided. However, according to your comment, the figure was modified and a legend and the scales were added to the map.

3) The conclusions do not discuss the results obtained with respect to other examples in literature which evaluate resilience with different approaches. E.g. just to cite a few:

Zhu et al. 2021. Enhancing urban flood resilience: A holistic framework incorporating historic worst flood to Yangtze River Delta, China.

Arrighi et al. 2022. Resilience of art cities to flood risk: A quantitative model based on depth-idleness correlation.

Bukvic et al., 2021. Exploring neighborhood-level resilience to flooding: Why the context and scale matter

Response 3: It is agreed that a comparison with the results obtained from the past studies is required and should be considered as a part of discussion in the results section. However, many studies on flood resilience (including the papers you mentioned as examples here) either didn’t investigated the resilience of urban drainage system directly or didn’t considered measuring the resilience sub-factors, i.e. their purpose was not quantifying the resilience indicators. Besides, the methodologies and results are far from the proposed methods and findings of current study. That’s why, due to a vast variety of differences, a detailed comparison of the results is not possible. The only similar study is the one performed by Tahmasebi Birgani and Yazdandoot (2014), which evaluated the UDS resilience based on three indicators of “reaction magnitude”, “graduality” and “recovery capacity”. However, even in their study, they didn’t calculate a final resilience index and only quantified some of the sub-factors of resilience. In addition, their study only considered the single-event rainfalls and they suggested including long-term events for evaluating the resilience of UDS.

Nevertheless, a comparison of the results was added to the results’ section and some more studies mentioned in the introduction section in comparison with the methodology in the current study.

4) The schemes of Fig. 1 and 4 have a poor resolution. In particular in Fig. 1 check also the consistencies of the terms used in the method section.

Response 4: The resolution of both figures 1 and 4 was improved as much as possible.

In figure 1, only Buffer Capacity was not directly referred to in the manuscript, and so, it was removed from the figure.

Reviewer 2 Report

The paper addresses the social and hydraulic resilience of a UDS with the use of the proposed index-based framework and an MCDM method. Both methodologies are well presented with the use of a case study, where calculations were made to estimate the system robustness as well as to quantify the system flexibility. The optimization of the UDS Resiliency was well examined using different scenarios for various UDS. The results produced were presented by the use of tables, and discussed further in order to indicate how the BMPs as a structural adaptive solutions improve the system resilience to flooding.

From the above it is concluded that the paper can be considered for publication in the present form.

Author Response

Response:  Thank you for your positive approach to this paper.

Round 2

Reviewer 1 Report

Authors have replied to the comments. The manuscript can be accepted.