the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 May 2024
Risk of compound flooding substantially increases in the future Mekong River delta
Abstract. Floods are consistently identified as the most serious global natural hazard, causing devastating loss of life and economic damages that run into multiple billions of dollars each year. At the coastline, many flood disasters are in fact compound flood events, with two or more flood drivers occurring concurrently or in quick succession. In coastal regions the combined effect of fluvial (river) and coastal (storm-tides – storm surges plus high astronomical tides) floods together has a greater impact than if each occurred separately. Deltas in south-east Asia are particularly exposed to coastal compound floods as they are low-lying, densely populated regions subject to both intense rainfall and tropical cyclone (TC) derived storm tides. For our study we used a sophisticated 1D river model, combined with 2D storm tide levels, to analyse past/present and future compound flood hazard and exposure for the Mekong River delta, one of the most flood-vulnerable deltas in the world. We found that with compound flooding a greater area of the delta will be inundated, some parts will flood to greater flood depth. Central areas around Ang Giang and the Dong Thap provinces would be particularly impacted. In the future delta, the impact of compound flooding is potentially more significant, as compound floods inundate a greater area, to greater depth in many locations, and floods last longer too. Compound flooding therefore has clear implications for flood managers of the future delta, who will need to ensure that existing and future flood defences are to the right standard and in the right locations to offer effective protection against this future risk.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(3230 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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- BibTeX
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-949', Anonymous Referee #1, 10 Jun 2024
The article "Risk of Compound Flooding Substantially Increases in the Future Mekong River Delta" explores the compounded impact of simultaneous or sequential river and coastal floods on the low-lying, densely populated Mekong River delta. Using advanced 1D and 2D modeling, the study examines flood hazards across past, present, and future scenarios. It finds that compound flooding will increasingly inundate larger areas and cause deeper floods, especially in central areas like Ang Giang and Dong Thap provinces. The study stresses the need for updated and robust flood defenses to mitigate these future risks.
Strengths
- Comprehensive Analysis: Combines historical data, advanced modeling, and future projections to thoroughly assess flood risks.
- Relevance: The focus on the Mekong River delta is timely, given the rising frequency of extreme weather events due to climate change.
- Detailed Methodology: Extensive descriptions of model setup, calibration, and validation add credibility.
- Clear Objectives: Clearly examines differences between single-source and compound flooding, changes over time, and flood-dominated regions.
Minor issues
- Model Limitations: Heavy reliance on assumptions and projections for future climate scenarios and river discharge estimates introduces uncertainties.
- Local Adaptations: The study suggests updating flood defenses but lacks in-depth discussion on specific local adaptation strategies or policy recommendations.
- Economic and Social Impacts: Insufficient analysis of the socio-economic consequences of increased flooding.
- Scope of Analysis: Only part of the document was reviewed, possibly omitting critical findings or discussions.
Overall:
The article provides essential insights into the future risks of compound flooding in the Mekong River delta, emphasizing the need for improved flood management strategies. It would further benefit from a deeper exploration of adaptive measures and a more detailed socio-economic impact assessment.
Citation: https://doi.org/10.5194/egusphere-2024-949-RC1 -
AC2: 'Reply on RC1', Melissa Wood, 02 Aug 2024
Kind thanks to this reviewer for their time to review this manuscript, and comments. In response to minor issue #1 we have inserted additional text to highlight the uncertainties inherent in the interpretation of these model results. In our conclusions section we inserted the following sentences:
“There are inherent uncertainties built into our modelled results, due to the series of assumptions made in the construction of future river discharges, and future extreme sea levels based on projections for our changing climate. Future studies could explore the bounds of this uncertainty with more data, or with new techniques”
For issues #2 and #3 raised, we fully agree that local adaption strategies and impact of policy recommendations are important, and are interesting things to consider in relation to the changing profile of compound flood hazard in this region. There is plenty of information publicly available where this could be more roundly explored. However, on these topics, and also on the socio-economic impacts of compound flooding, we feel (especially given that the length of the existing document is already long), that these avenues go beyond the scope of the aims and objectives of the original manuscript. Instead, we have named these as specific recommendations for future study, and within the conclusions section we have added the following paragraph:
“... there are clear socio-economic impacts from compound flooding and future studies could explore this more widely. In our analysis we employed a scenario assuming a worst case scenario of a TC strike and river flood peak occurring almost concurrently, at a date in the middle of the wet season. Variations of this set up will alter model outcomes and be interesting to explore. In particular, the compound hazard where TCs make landfall at different locations/orientations has not been explored here, nor the impact of compound flooding in a delta with changing morphologies due to sand mining, coastal development, or land subsidence. These topics could also be interesting and rewarding areas of future research”Citation: https://doi.org/10.5194/egusphere-2024-949-AC2
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RC2: 'Comment on egusphere-2024-949', Anonymous Referee #2, 19 Jun 2024
This paper investigates future risk of compound flood in the Mekong River delta using 1D river and 2D coastal models. It provides detailed analysis of compound flood risk in the delta, particularly intriguing the results of the compound ratio in Figure 8 showing that even inland areas may be susceptible to compound flooding. The paper itself is well written and fits the scope of the journal NHESS.
I only found it a minor concern that the introduction part does not clarify the research gap of past studies and the scientific question that should be addressed in the present study. In page 3 line 88– the objective is described, but it does not mention its scientific significance, making the paper look a technical report at a specific region. Therefore, minor revision is necessary before being considered for publication.
Citation: https://doi.org/10.5194/egusphere-2024-949-RC2 -
AC1: 'Reply on RC2', Melissa Wood, 02 Aug 2024
Kind thanks to this anonymous reviewer for their time and comments. We have rewritten parts of the introduction in order to better frame the scientific gap and question behind this study, as suggested. The following paragraph has been inserted before the text outlining our three core objectives:
“Despite it being an economic powerhouse for the region, and it’s strategic value to regional food security, no research has been carried out specifically to look at TC-linked compound flood risk within the wider Mekong River delta area. The recent work of Rodrigues do Amaral et al., (2023) explored the compound flood hazards to the adjacent city of Ho Chi Minh, from Typhoon Usagi (2018) and found that river flooding and rainfall runoff caused flooding up to 0.8m because of the co-occurrence of high sea levels which prevented normal drainage. However, Ho Chi Minh City is not within the large Mekong River delta catchment. Triet at al., (2020) assessed the combined impacts of climate change: increased river discharges, and rising sea levels (including tides), on the future (2036-2065) Mekong River delta assuming representative concentration pathway (RCP) number 4.5. This was within the context of continued hydropower development within the catchment. They found that flood waters would submerge some new areas, and prolong the flood in some parts of the delta by an additional 1-2 months. However, neither of these studies examine multi-driver or compound flood risk from TC activity in the delta, specifically the combination of river flooding combined with TC-linked storm surges at the coastline. The research question for this study is therefore, “how is the Mekong River delta impacted by compound flooding linked to TC-activity in the region (river flooding + storm surges), and to what extent will these impacts change due to climate change by year 2050?”Citation: https://doi.org/10.5194/egusphere-2024-949-AC1
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AC1: 'Reply on RC2', Melissa Wood, 02 Aug 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-949', Anonymous Referee #1, 10 Jun 2024
The article "Risk of Compound Flooding Substantially Increases in the Future Mekong River Delta" explores the compounded impact of simultaneous or sequential river and coastal floods on the low-lying, densely populated Mekong River delta. Using advanced 1D and 2D modeling, the study examines flood hazards across past, present, and future scenarios. It finds that compound flooding will increasingly inundate larger areas and cause deeper floods, especially in central areas like Ang Giang and Dong Thap provinces. The study stresses the need for updated and robust flood defenses to mitigate these future risks.
Strengths
- Comprehensive Analysis: Combines historical data, advanced modeling, and future projections to thoroughly assess flood risks.
- Relevance: The focus on the Mekong River delta is timely, given the rising frequency of extreme weather events due to climate change.
- Detailed Methodology: Extensive descriptions of model setup, calibration, and validation add credibility.
- Clear Objectives: Clearly examines differences between single-source and compound flooding, changes over time, and flood-dominated regions.
Minor issues
- Model Limitations: Heavy reliance on assumptions and projections for future climate scenarios and river discharge estimates introduces uncertainties.
- Local Adaptations: The study suggests updating flood defenses but lacks in-depth discussion on specific local adaptation strategies or policy recommendations.
- Economic and Social Impacts: Insufficient analysis of the socio-economic consequences of increased flooding.
- Scope of Analysis: Only part of the document was reviewed, possibly omitting critical findings or discussions.
Overall:
The article provides essential insights into the future risks of compound flooding in the Mekong River delta, emphasizing the need for improved flood management strategies. It would further benefit from a deeper exploration of adaptive measures and a more detailed socio-economic impact assessment.
Citation: https://doi.org/10.5194/egusphere-2024-949-RC1 -
AC2: 'Reply on RC1', Melissa Wood, 02 Aug 2024
Kind thanks to this reviewer for their time to review this manuscript, and comments. In response to minor issue #1 we have inserted additional text to highlight the uncertainties inherent in the interpretation of these model results. In our conclusions section we inserted the following sentences:
“There are inherent uncertainties built into our modelled results, due to the series of assumptions made in the construction of future river discharges, and future extreme sea levels based on projections for our changing climate. Future studies could explore the bounds of this uncertainty with more data, or with new techniques”
For issues #2 and #3 raised, we fully agree that local adaption strategies and impact of policy recommendations are important, and are interesting things to consider in relation to the changing profile of compound flood hazard in this region. There is plenty of information publicly available where this could be more roundly explored. However, on these topics, and also on the socio-economic impacts of compound flooding, we feel (especially given that the length of the existing document is already long), that these avenues go beyond the scope of the aims and objectives of the original manuscript. Instead, we have named these as specific recommendations for future study, and within the conclusions section we have added the following paragraph:
“... there are clear socio-economic impacts from compound flooding and future studies could explore this more widely. In our analysis we employed a scenario assuming a worst case scenario of a TC strike and river flood peak occurring almost concurrently, at a date in the middle of the wet season. Variations of this set up will alter model outcomes and be interesting to explore. In particular, the compound hazard where TCs make landfall at different locations/orientations has not been explored here, nor the impact of compound flooding in a delta with changing morphologies due to sand mining, coastal development, or land subsidence. These topics could also be interesting and rewarding areas of future research”Citation: https://doi.org/10.5194/egusphere-2024-949-AC2
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RC2: 'Comment on egusphere-2024-949', Anonymous Referee #2, 19 Jun 2024
This paper investigates future risk of compound flood in the Mekong River delta using 1D river and 2D coastal models. It provides detailed analysis of compound flood risk in the delta, particularly intriguing the results of the compound ratio in Figure 8 showing that even inland areas may be susceptible to compound flooding. The paper itself is well written and fits the scope of the journal NHESS.
I only found it a minor concern that the introduction part does not clarify the research gap of past studies and the scientific question that should be addressed in the present study. In page 3 line 88– the objective is described, but it does not mention its scientific significance, making the paper look a technical report at a specific region. Therefore, minor revision is necessary before being considered for publication.
Citation: https://doi.org/10.5194/egusphere-2024-949-RC2 -
AC1: 'Reply on RC2', Melissa Wood, 02 Aug 2024
Kind thanks to this anonymous reviewer for their time and comments. We have rewritten parts of the introduction in order to better frame the scientific gap and question behind this study, as suggested. The following paragraph has been inserted before the text outlining our three core objectives:
“Despite it being an economic powerhouse for the region, and it’s strategic value to regional food security, no research has been carried out specifically to look at TC-linked compound flood risk within the wider Mekong River delta area. The recent work of Rodrigues do Amaral et al., (2023) explored the compound flood hazards to the adjacent city of Ho Chi Minh, from Typhoon Usagi (2018) and found that river flooding and rainfall runoff caused flooding up to 0.8m because of the co-occurrence of high sea levels which prevented normal drainage. However, Ho Chi Minh City is not within the large Mekong River delta catchment. Triet at al., (2020) assessed the combined impacts of climate change: increased river discharges, and rising sea levels (including tides), on the future (2036-2065) Mekong River delta assuming representative concentration pathway (RCP) number 4.5. This was within the context of continued hydropower development within the catchment. They found that flood waters would submerge some new areas, and prolong the flood in some parts of the delta by an additional 1-2 months. However, neither of these studies examine multi-driver or compound flood risk from TC activity in the delta, specifically the combination of river flooding combined with TC-linked storm surges at the coastline. The research question for this study is therefore, “how is the Mekong River delta impacted by compound flooding linked to TC-activity in the region (river flooding + storm surges), and to what extent will these impacts change due to climate change by year 2050?”Citation: https://doi.org/10.5194/egusphere-2024-949-AC1
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AC1: 'Reply on RC2', Melissa Wood, 02 Aug 2024
Peer review completion
Journal article(s) based on this preprint
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- 1
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Melissa Wood
Ivan D. Haigh
Quan Quan Le
Hung Nghia Nguyen
Hoang Tran Ba
Stephen E. Darby
Robert Marsh
Nikolaos Skliris
Joël J.-M. Hirschi
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3230 KB) - Metadata XML