the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Uncovering Inundation Hotspots through a Normalized Flood Severity Index: Urban Flood Modelling Based on Open-Access Data in Ho Chi Minh City, Vietnam
Mazen Hoballah Jalloul
Leon Scheiber
Christian Jordan
Jan Visscher
Hong Quan Nguyen
Torsten Schlurmann
Abstract. Hydro-numerical models offer an increasingly important tool to determine the adequacy and evaluate the effectiveness of potential flood protection measures. However, a significant obstacle in setting up hydro-numerical and associated flood damage models is the tedious and oftentimes prohibitively costly process of acquiring reliable input data, which particularly applies to coastal megacities in developing countries and emerging economies. To address this problem, this paper takes the example of Ho Chi Minh City, Vietnam, and proposes a new and comprehensive methodology for acquiring, processing, and applying the necessary open-access data (topography, bathymetry, tidal, river flow, and precipitation time series) to set up an urban surface run-off model. As a key novelty of the paper, a normalized flood severity index (NFSI) that combines flood depth and duration is proposed. The index serves as an indicator that helps uncover urban inundation hotspots with severe damage potential, drawing attention to specific districts or boroughs with special adaptation needs or emergency response measures. The approach is validated by comparison with more than 300 locally reported flood samples, which correspond to NFSI-processed inundation hotspots in over 73 % of all cases. These findings corroborate the robustness of the proposed index, which may significantly enhance the interpretation and trustworthiness of hydro-numerical assessments in the future. The proposed approach and developed indicators are generic and may be replicated and adopted in other coastal megacities.
Mazen Hoballah Jalloul et al.
Status: closed
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RC1: 'Comment on nhess-2022-238', Anonymous Referee #1, 12 Oct 2022
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AC1: 'Reply on RC1', Leon Scheiber, 23 Dec 2022
Dear Reviewer,
we would like to express our sincere gratitude for the time and effort you invested in studying our manuscript and for the valuable feedback you provided. You may now find our response letter attached to this comment.
Thank you and kind regards,
Leon Scheiber
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AC1: 'Reply on RC1', Leon Scheiber, 23 Dec 2022
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RC2: 'Comment on nhess-2022-238', Anonymous Referee #2, 09 Nov 2022
General comments:
The paper demonstrated how to process and applying open-access data to an urban surface run-off model. The authors also combined flood depth and duration into a so-called normalized flood severity index (NFSI) to identify urban inundation hotspots. Overall, this paper might be useful in demonstrating how open access data can be processed into hydrological model. However, the methodology to achieve this need to be more systematically presented. Whether this methodology can be considered novel or not is unclear as the process seemed quite intuitive. Besides, the applicability of the research is thin. Vulnerability assessment is being conducted in cities to identify the areas that need response measures. Moreover, the application of the flood severity index is rather thin. As mentioned above, inundation hotspots can be identified through vulnerability assessment. The thresholds for the NFSI were not mentioned. What insights or new implications can be extracted from using the NFSI?
How can the data processing method be applied to other megacities? Why the authors selected HCMC for model validation? Why not different locations around the planet?
Specific comments:
Line 24: adaptation to what, increasing precipitation? Sea level rise? Usually, adaptation refers to responses to changing risk. I don’t think it is applicable to this manuscript. In this case it is more like responding to floods.
Line 55 – 59: why there is a need for the complete surface runoff model while vulnerability assessment is being conducted? What is the application of the proposed flood severity index?
Line 66: how about flood frequency? Why is flood frequency excluded from this index?
Table 1: this table can be improved by incorporating errors or each DEM, and how these errors can be addressed.
Figure 2: if my understanding is right, it should be: subtract (c) from (b) rather than add (b) to (c).
Line 172 – 174: how about natural waterways inside HCMC? There is informal settlement encroaching on natural waterways inside HCMC, which also get flooded frequently during high tides and heavy rains (ex. Tran Xuan Soan street).
Line 231: why not using data from Phu An station?
Line 244: why an eight-day time series?
Line 261: why only a 2-year flood selected? How about 5-year, 10-year floods?
Comment for the 2.2. section: How about reservoirs and groundwater? Why are these excluded from the model?
Method section: there should be one graph summarize the proposed methodology. So far, these are scatter over different section of each type of date, which is difficult to grasp the bif picture of the proposed methodology. Besides, methodology for processing each element should be presented in equation form rather than figures (i.e., figure 2 and figure 7).
Line 335: what do the authors mean by the threshold of the NFSI is at its maximum? Maximum of what? How are the factors of changing climate considered? Why did the authors give equal weights to flood depth and duration? How about flood frequency?
Citation: https://doi.org/10.5194/nhess-2022-238-RC2 -
AC2: 'Reply on RC2', Leon Scheiber, 23 Dec 2022
Dear Reviewer,
on behalf of all co-authors, I would like to express our sincere gratitude for the time and effort you invested in studying our manuscript and for the valuable feedback you provided. You may now find our response letter attached to this comment.
Thank you and kind regards,
Leon Scheiber
-
AC2: 'Reply on RC2', Leon Scheiber, 23 Dec 2022
Status: closed
-
RC1: 'Comment on nhess-2022-238', Anonymous Referee #1, 12 Oct 2022
-
AC1: 'Reply on RC1', Leon Scheiber, 23 Dec 2022
Dear Reviewer,
we would like to express our sincere gratitude for the time and effort you invested in studying our manuscript and for the valuable feedback you provided. You may now find our response letter attached to this comment.
Thank you and kind regards,
Leon Scheiber
-
AC1: 'Reply on RC1', Leon Scheiber, 23 Dec 2022
-
RC2: 'Comment on nhess-2022-238', Anonymous Referee #2, 09 Nov 2022
General comments:
The paper demonstrated how to process and applying open-access data to an urban surface run-off model. The authors also combined flood depth and duration into a so-called normalized flood severity index (NFSI) to identify urban inundation hotspots. Overall, this paper might be useful in demonstrating how open access data can be processed into hydrological model. However, the methodology to achieve this need to be more systematically presented. Whether this methodology can be considered novel or not is unclear as the process seemed quite intuitive. Besides, the applicability of the research is thin. Vulnerability assessment is being conducted in cities to identify the areas that need response measures. Moreover, the application of the flood severity index is rather thin. As mentioned above, inundation hotspots can be identified through vulnerability assessment. The thresholds for the NFSI were not mentioned. What insights or new implications can be extracted from using the NFSI?
How can the data processing method be applied to other megacities? Why the authors selected HCMC for model validation? Why not different locations around the planet?
Specific comments:
Line 24: adaptation to what, increasing precipitation? Sea level rise? Usually, adaptation refers to responses to changing risk. I don’t think it is applicable to this manuscript. In this case it is more like responding to floods.
Line 55 – 59: why there is a need for the complete surface runoff model while vulnerability assessment is being conducted? What is the application of the proposed flood severity index?
Line 66: how about flood frequency? Why is flood frequency excluded from this index?
Table 1: this table can be improved by incorporating errors or each DEM, and how these errors can be addressed.
Figure 2: if my understanding is right, it should be: subtract (c) from (b) rather than add (b) to (c).
Line 172 – 174: how about natural waterways inside HCMC? There is informal settlement encroaching on natural waterways inside HCMC, which also get flooded frequently during high tides and heavy rains (ex. Tran Xuan Soan street).
Line 231: why not using data from Phu An station?
Line 244: why an eight-day time series?
Line 261: why only a 2-year flood selected? How about 5-year, 10-year floods?
Comment for the 2.2. section: How about reservoirs and groundwater? Why are these excluded from the model?
Method section: there should be one graph summarize the proposed methodology. So far, these are scatter over different section of each type of date, which is difficult to grasp the bif picture of the proposed methodology. Besides, methodology for processing each element should be presented in equation form rather than figures (i.e., figure 2 and figure 7).
Line 335: what do the authors mean by the threshold of the NFSI is at its maximum? Maximum of what? How are the factors of changing climate considered? Why did the authors give equal weights to flood depth and duration? How about flood frequency?
Citation: https://doi.org/10.5194/nhess-2022-238-RC2 -
AC2: 'Reply on RC2', Leon Scheiber, 23 Dec 2022
Dear Reviewer,
on behalf of all co-authors, I would like to express our sincere gratitude for the time and effort you invested in studying our manuscript and for the valuable feedback you provided. You may now find our response letter attached to this comment.
Thank you and kind regards,
Leon Scheiber
-
AC2: 'Reply on RC2', Leon Scheiber, 23 Dec 2022
Mazen Hoballah Jalloul et al.
Mazen Hoballah Jalloul et al.
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