the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 May 2025
Mitigating the Impact of Increased Drought-Flood Abrupt Alternation Events under Climate Change: The Role of Reservoirs in the Lancang-Mekong River Basin
Abstract. The Lancang-Mekong River (LMR) Basin is highly vulnerable to extreme hydrological events, including Drought-Flood Abrupt Alternation (DFAA). The impact of climate change on DFAA and the efficacy of potential mitigation measures such as reservoirs remain poorly understood. This study investigates these dynamics using five Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6). It employs the Revised Short-cycle Drought-Flood Abrupt Alteration Index (R-DFAI), alongside the Tsinghua Representative Elementary Watershed (THREW) model integrated with the developed reservoir module. Results reveal that future DFAA trend varies widely in upstream and downstream, with significant increases respectively in FTD (flood to drought) upstream and DTF (drought to flood) downstream. FTD is more challenging though DTF is more probable to occur. Under SSP126 and SSP245 scenarios, DFAA risks escalate, especially during the wet season, whereas under SSP585, these risks decline. Reservoirs as a promising adaptation strategy can significantly mitigate year-round DTF and wet season's FTD, particularly in regions with higher total reservoir storage. Reservoir operations reduce DFAA's intensity, limit multiple peaks and shorten its monthly span. Hydrological forecasting and resilient storage enables to be viable options for climate change to help LMR Basin smooth out DFAA. These insights offer valuable guidance for effective water resource cooperative management across LMR Basin countries.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Hydrology and Earth System Sciences.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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RC1: 'Comment on egusphere-2025-1126', Anonymous Referee #1, 20 Jun 2025
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This paper analysed the Drought-Flood Abrupt Alternation (DFAA) in the Lancang-Mekong River Basin under three climate projection scenarios from five Global Climate Models (GCMs) of CMIP6. Authors found that future DFAA trend varies widely in upstream and downstream and reservoirs operations can reduce DFAA’s intensity, limit multiple peaks and shorten the monthly span. The paper is structured, however, there are some concerns.
- The introduction lacks sufficient discussion and comparison with recently published studies that examine the role of reservoir modules in hydrological modeling under climate projections.
- Authors mentioned CMIP6 data collected from five GCMs, but only show the averaged meteorological data. Since each GCM may incorporate different assumptions and mechanisms for projecting climate variables, relying solely on the mean values could introduce bias or obscure important variability. If averaging is justified, please provide a clear rationale.
- Please list the equations to calculate the Standardized Runoff Index (SRI).
- It is unclear that how the probability calculates in equation (22).
- While the results show changes in indicator probabilities across different scenarios and time scales, the influence of reservoir operations on DFAA remains unclear. Are the operations temporally and spatially variable? Further clarification is necessary to understand the extent and mechanism of reservoir operations.
- Are the reservoirs operations the dominant factor of DFAA events in the Lancang-Mekong River Basin? Please comment it.
Citation: https://doi.org/10.5194/egusphere-2025-1126-RC1 -
RC2: 'Comment on egusphere-2025-1126', Anonymous Referee #2, 22 Jun 2025
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This study evaluated the impacts of climate change and reservoir operations on Drought-Flood Abrupt Alternation (DFAA) using five Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) in the Lancang-Mekong River Basin. The authors have contributed to the understanding of future DFAA. But there are still some issues that need to be clarified:
1. Line 18: It is recommended to describe the results using the conditions of the emission scenario rather than the version of the scenario.
2. Line 36: Please supplement which secondary disasters.
3. Line 63: How did previous hydrological models simulate DFAA? How has the reservoir module progressed in hydrological models?
4. Line 78: Where is the population data obtained?
5. Line 100: Are there any other GCMs? Are only these five available, or do these five have better effects?
6. Section 2.2: There need usage instructions for the data. For instance, if the precipitation and temperature of ERA5 are used to correct GCMs, then what is the potential evapotranspiration used for?
7. Section 2.3: As the core method of this section, the main formulas of MBG should be listed.
8. Section 2.4: Why are Formula 3 and Formula 8 repeated? Can so many simple formulas be explained in the main text? The principle of reservoir allocation is suggested to be shown in a schematic diagram because these formulas are both numerous and simple.
9. Line 145: For the complex physical mechanisms in the model, there are no formulas at all? What are the equilibrium equations, geometrical relationships, and constitutive relationships in the model? The Nash efficiency coefficient is relatively less necessary to present.
10. Section 2.4: The GCM model is spatially distributed grid data, and the reservoir here is a lumped water distribution. How can a simple lumped water distribution be regulated regionally?
11. Line 215: I thought that the five GCMs used for simulation could mutually test the reliability, but here the average value was directly used without analyzing the sensitivity of the five models. GCMs’ errors are not complementary. Some may be more accurate, while others have larger errors. A simple average value is of no help to the research.
12. Line 214: According to the abstract, "Reservoir operations reduce DFAA's intensity." It should be getting the intensity of the DFAA, why there is a probability, and how to quantify intensity.
13. Please pay attention to the garbled characters that appear in lines 156, 242, and 243.
14. When many formulas are piled up and there are no corresponding textual descriptions, it is very difficult to know what the logic between them is. Here, it is necessary to select the most important ones from these formulas for listing and then describe the logic of the formulas. Furthermore, what’s these methods’ regional applicability? What are their advantages and limitations?
15. Section 3.1: Since the study originally used ERA5 for correction, it doesn't mean that being closer to ERA5 is accurate. ERA5 also has errors. It can only be said that after correction, the GCM is closer to ERA5, and this cannot be used as an accurate basis here. Even this subsection can be transformed into a description of the spatiotemporal distribution of climate data.
16. Section 3.2: The absence of reservoirs before 2009 and the existence of reservoirs after 2010 should be very important background. When the coupled reservoir module is used for DFAA simulation, it should be simulated in segments. For those after 2010, additional reservoirs should be added. What will the situation of reservoirs be like in future scenarios? This needs to be explained in the summary and subsequent sections of the DFAA results.
17. Section 3.3: Shouldn't this probability be compared with the occurrence of a single disaster before? The probability can be calculated based on the time within a year.
18. Section 3.4: How will the future reservoir operation information be obtained?
19. The discussion section should use more literature to support the causes and reliability of the results. Here, for example, in the first part of the discussion, except for the first sentence, which is cited, the rest is all about explaining the results.
20. The second part of the discussion talked about the reservoir's ability to respond to DFAA. Here, in addition to considering the changes in the water volume of the reservoir, it is also necessary to consider how long the reservoir operation occurred before or after the disaster. The occurrence time of reservoir operation will have a timely impact on the specific disaster.
21. The discussion in the third part also rarely cites literature, and the utilization of the resilient storage should not be the focus of the discussion in this article. The focus is on the influence of the reservoir in the process of disaster simulation.
22. In addition, the bar charts and line charts from Figure 4 to Figure 6 are all numbers that can be presented in a table, and the richness of the accompanying figures should be increased.
Citation: https://doi.org/10.5194/egusphere-2025-1126-RC2
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