the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Low-regret Climate Change Adaptation in Coastal Megacities – Evaluating Large-Scale Flood Protection and Small-Scale Rainwater Detention Measures for Ho Chi Minh City, Vietnam
Leon Scheiber
C. Gabriel David
Mazen Hoballah Jalloul
Jan Visscher
Hong Quan Nguyen
Roxana Leitold
Javier Revilla Diez
Torsten Schlurmann
Abstract. The risk of urban flooding is a major challenge for many megacities in low elevation coastal zones (LECZ), especially in Southeast Asia. Here, the effects of environmental stressors overlap with rapid urbanization, which significantly aggravates the hazard potential in these regions. Ho Chi Minh City (HCMC) in Southern Vietnam is a prime example of this set of problems and therefore a meaningful study case to apply the concept of low-regret disaster risk adaptation as defined by the Intergovernmental Panel on Climate Change (IPCC). In order to explore and evaluate potential options for hazard mitigation, a hydro-numerical model was employed to scrutinize the effectiveness of two adaptation strategies: (1) a large-scale flood protection scheme as currently constructed in HCMC and (2) the widespread installation of small-scale rainwater detention as envisioned in the framework of the Chinese Sponge City Program (SPM). A third adaptation scenario (3) assesses the combined implementation of both approaches (1) and (2).
From a hydrological point of view, the reduction of various flood intensity proxies suggests that the effectiveness of large-scale flood protection outweighs that of small-scale rainwater storage by far. For example, an assessment of the Normalized Flood Severity Index (NFSI) suggests a potential flood reduction that is 3.5 times higher for a classic infrastructure solution than for the Sponge City approach. In contrast, the number of manufacturing firms that are protected from risk after the implementation of disaster risk adaptation significantly excels for the latter response option: while the ring dike mitigates flooding at about 20 % of all considered locations, the assumed rainwater detention would protect up to 93 %. And also, from a governance perspective, decentralized rainwater storage conforms better to the low-regret paradigm: while the large-scale ring dike depends on a binary commitment (to build or not to build), decentralized small- and micro-scale solutions can be implemented gradually (through targeted subsidies) and add technical redundancy to the overall system. In the end, both strategies are highly complementary in their spatial and temporal reduction of flood intensity, so local decision-makers may specifically seek multi-faceted strategies, avoiding singular approaches and designing adaptation pathways in order to successfully prepare for a deeply uncertain future.
Leon Scheiber et al.
Status: closed
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RC1: 'Comment on nhess-2022-239', Anonymous Referee #1, 04 Nov 2022
This paper compares the effectiveness of two adaptation strategies: (1) a large-scale flood
protection scheme as currently constructed in HCMC and (2) the widespread installation of small-scale rainwater detention as envisioned in the framework of the Chinese Sponge City Program (SPM). As authors claimed, it is important to explore and evaluate potential options of hazard mitigation as flood risk is becoming a major challenge for many cities in low elevation coastal zones. The topic of this study is valuable. But the quality and innovation of the current manuscript are not satisfactory. In any case, I have a few recommendations that I believe will help the authors to clarify their contribution and improve the readability of the manuscript.
Specific points are:
- Most of the figures in the manuscript are very poor in quality and hard to meet the standard for this journal, such as Figs. 2, not clear enough. Generally some of the figures are too small.
- How to simulate the small-scale rainwater detention in the HEC-RAS model? What is the limitation or uncertainty?
- I am not convinced by the model setup given limited information, more information for the validity of flood simulation by HEC-RAS should be described in the paper.
- What is " Flood Severity Index (NFSI) ", how is it measured?
- Drainage capacity should be considered for the flood simulation.
- In Table 1, Flood depth (dmax) is the average for all the raster cells? This seems very simple. More analysis should be done for different cells, especially considering the spatial distribution.
- Spatial distribution of Flood Severity (NFSI) for different cells?
- This study only considers three scenarios of the mitigation scenarios, I think more analysis considering different sponge city measures would be very interesting. You will want to discuss this.
Citation: https://doi.org/10.5194/nhess-2022-239-RC1 -
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 best regards,
Leon Scheiber
-
RC2: 'Comment on nhess-2022-239', Anonymous Referee #2, 14 Nov 2022
This study presents an interesting topic on low-regret climate change adaption for flood hazard in Ho Chi Minh City of Vietnam. The study has compared the effectiveness of three techniques in flood adaption strategies including: (1) a large-scale protection project using a ring dike; (2) a small-scale rainwater detention scheme; and (3) a combined application of both strategies.
The authors should consider the following specific points:
- Please include a flowchart of data processing in the manuscript for better understanding of the framework of this study.
- How the Normalized Flood Severity Index (NFSI) was generated from the input parameters?
- Line 162: Using reported data in 2010 for validation of the model is out of date. Please use the most recent field data for evaluation.
- Figure 2: all of the legends in this figure should be more clearly presented.
Citation: https://doi.org/10.5194/nhess-2022-239-RC2 -
AC2: 'Reply on RC2', 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 best regards,
Leon Scheiber
-
AC2: 'Reply on RC2', Leon Scheiber, 23 Dec 2022
Status: closed
-
RC1: 'Comment on nhess-2022-239', Anonymous Referee #1, 04 Nov 2022
This paper compares the effectiveness of two adaptation strategies: (1) a large-scale flood
protection scheme as currently constructed in HCMC and (2) the widespread installation of small-scale rainwater detention as envisioned in the framework of the Chinese Sponge City Program (SPM). As authors claimed, it is important to explore and evaluate potential options of hazard mitigation as flood risk is becoming a major challenge for many cities in low elevation coastal zones. The topic of this study is valuable. But the quality and innovation of the current manuscript are not satisfactory. In any case, I have a few recommendations that I believe will help the authors to clarify their contribution and improve the readability of the manuscript.
Specific points are:
- Most of the figures in the manuscript are very poor in quality and hard to meet the standard for this journal, such as Figs. 2, not clear enough. Generally some of the figures are too small.
- How to simulate the small-scale rainwater detention in the HEC-RAS model? What is the limitation or uncertainty?
- I am not convinced by the model setup given limited information, more information for the validity of flood simulation by HEC-RAS should be described in the paper.
- What is " Flood Severity Index (NFSI) ", how is it measured?
- Drainage capacity should be considered for the flood simulation.
- In Table 1, Flood depth (dmax) is the average for all the raster cells? This seems very simple. More analysis should be done for different cells, especially considering the spatial distribution.
- Spatial distribution of Flood Severity (NFSI) for different cells?
- This study only considers three scenarios of the mitigation scenarios, I think more analysis considering different sponge city measures would be very interesting. You will want to discuss this.
Citation: https://doi.org/10.5194/nhess-2022-239-RC1 -
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 best regards,
Leon Scheiber
-
RC2: 'Comment on nhess-2022-239', Anonymous Referee #2, 14 Nov 2022
This study presents an interesting topic on low-regret climate change adaption for flood hazard in Ho Chi Minh City of Vietnam. The study has compared the effectiveness of three techniques in flood adaption strategies including: (1) a large-scale protection project using a ring dike; (2) a small-scale rainwater detention scheme; and (3) a combined application of both strategies.
The authors should consider the following specific points:
- Please include a flowchart of data processing in the manuscript for better understanding of the framework of this study.
- How the Normalized Flood Severity Index (NFSI) was generated from the input parameters?
- Line 162: Using reported data in 2010 for validation of the model is out of date. Please use the most recent field data for evaluation.
- Figure 2: all of the legends in this figure should be more clearly presented.
Citation: https://doi.org/10.5194/nhess-2022-239-RC2 -
AC2: 'Reply on RC2', 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 best regards,
Leon Scheiber
-
AC2: 'Reply on RC2', Leon Scheiber, 23 Dec 2022
Leon Scheiber et al.
Leon Scheiber et al.
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