Overtopping risk of high-hazard embankment dam under climate change condition

crest level, necessitating comprehensive risk management strategies. Structural reinforce- ments, increased monitoring, and emergency preparedness plans are critical to mitigate the severe impacts projected. However, projections for the Early Century (2020–2046) indicate a significant increase in water levels, particularly for higher Average Recurrence Intervals (ARIs). In some scenarios, water levels approach the crest level, suggesting a growing risk of overtopping. This increase can be attributed to the anticipated changes in precipitation patterns and intensities due to cli- mate change. Studies such as those by [35] highlight the need for adaptive strategies to manage these increased risks in the near future. The Mid Century (2047–2073) projections present a more alarming scenario, with several ARI conditions exceeding the crest level, particularly under RCP 6.0 and RCP 8.5 scenarios. This suggests a tangible overtopping risk that could lead to dam failure if not addressed through structural and operational interventions. [31] emphasize the importance of integrat- ing climate projections into dam safety assessments to preemptively mitigate such risks. Looking further into the Late Century (2074–2100), the projections show the highest exceedances of the crest level, with multiple ARI values surpassing it. This period is marked by a severe overtopping risk, especially under the RCP 8.5 scenario, which represents the highest greenhouse gas concentration pathway [31, 35]. The findings by [42] reinforce the critical

need for robust risk-informed decision-making frameworks to enhance the resilience of embankment dams against the increasingly severe impacts of climate change. These projections underscore the urgency for proactive measures, including raising crest levels, enhancing spillway capacities, and adopting comprehensive risk management strategies to ensure the continued safety and functionality of embankment dams in the face of escalating climatic threats The findings from [31, 35] support these trends, indicating that climate change Fig 12. IDF Curve of Mid Century under scenario (a) RCP 4.5, (b) RCP 6.0, and (c) RCP 8.5. Rainfall Intensity vs. Duration for Various Average Recurrence Intervals (ARI), illustrating the decrease in intensity with longer storm durations across different ARI events, ranging from 1-year to 100,000-year return periods. https://doi.org/10.1371/journal.pone.0311181.g012 PLOS ONE Climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0311181 February 27, 2025 21 / 32

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substantially increases the likelihood of dam overtopping and failure, especially under the high emissions RCP 8.5 scenario. Discussion and conclusions This study underscores the significant implications of climate change on the safety of embank- ment dams, particularly highlighting the increasing risk of overtopping under various climate scenarios. The analysis of historical data (1975–2019) and projections for the early, mid, and late 21st century under RCP 4.5, 6.0, and 8.5 scenarios reveals a clear trend of rising water lev- els and heightened overtopping risks. This study underscores the importance of integrating cli- mate change projections into dam safety management. The findings highlight the need for immediate and long-term adaptive strategies to address the increasing risks posed by higher inflows and potential overtopping. Ensuring the safety and resilience of embankment dams under future climate scenarios will require a combination of structural enhancements, rigorous monitoring, and adaptive management practices. Conse- quently, the dam owner must remain vigilant and prepared for future inflow events. Utilizing the future prediction inflow return period can serve as a basis for determining dam decision- making strategies to reduce the impact of discharge on the surrounding community. Ensuring the dam’s safety and resilience against changing climate scenarios is paramount to safeguard- ing the dam infrastructure and the people living downstream. Addressing this challenge requires a multi-faceted approach that integrates climate adaptation

strategies, infrastructure resilience measures, and robust emergency preparedness protocols. By implementing proactive measures, monitoring systems, and structural upgrades, stakeholders can effectively mitigate the risk of dam overtopping and enhance the safety of communities and eco- systems downstream. Collaboration between government agencies, engineering professionals, and local communities is essential to navigate the complex dynamics of climate change and ensure the sustainable management of embankment dam at Batu Dam, in Malaysia. Fig 13. IDF Curve of Late Century under scenario (a) RCP 4.5, (b) RCP 6.0, and (c) RCP 8.5. Rainfall Intensity vs. Duration for Various Average Recurrence Intervals (ARI), illustrating the decrease in intensity with longer storm durations across different ARI events, ranging from 1-year to 100,000-year return periods. https://doi.org/10.1371/journal.pone.0311181.g013 Fig 14. Example PMF simulation of Batu Dam. Flow vs. Time for Various Durations, highlighting peak discharge rates for rainfall events from 1 hour to 5 days. https://doi.org/10.1371/journal.pone.0311181.g014 PLOS ONE Climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0311181 February 27, 2025 23 / 32

Fig 15. Historical peak inflow design flood at Batu Dam. Flow hydrographs showing peak discharge for ranging from 5 ARI to 100,000 ARI and the Probable Maximum Flood (PMF), illustrating the increase in peak flow with higher ARIs and extreme events. https://doi.org/10.1371/journal.pone.0311181.g015 Fig 16. RCP4.5 early century peak inflow design flood at Batu Dam. Flow hydrographs showing peak discharge for ranging from 5 ARI to 100,000 ARI and the Probable Maximum Flood (PMF), illustrating the increase in peak flow with higher ARIs and extreme events. https://doi.org/10.1371/journal.pone.0311181.g016 PLOS ONE Climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0311181 February 27, 2025 24 / 32

Fig 18. RCP8.5 early century peak inflow design flood at Batu Dam. Flow hydrographs showing peak discharge for ranging from 5 ARI to 100,000 ARI and the Probable Maximum Flood (PMF), illustrating the increase in peak flow with higher ARIs and extreme events. https://doi.org/10.1371/journal.pone.0311181.g018 Fig 17. RCP6.0 early century peak inflow design flood at Batu Dam. Flow hydrographs showing peak discharge for ranging from 5 ARI to 100,000 ARI and the Probable Maximum Flood (PMF), illustrating the increase in peak flow with higher ARIs and extreme events. https://doi.org/10.1371/journal.pone.0311181.g017 PLOS ONE Climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0311181 February 27, 2025 25 / 32

Fig 20. RCP6.0 mid century peak inflow design flood at Batu Dam. Flow hydrographs showing peak discharge for ranging from 5 ARI to 100,000 ARI and the Probable Maximum Flood (PMF), illustrating the increase in peak flow with higher ARIs and extreme events. https://doi.org/10.1371/journal.pone.0311181.g020 Fig 19. RCP4.5 mid century peak inflow design flood at Batu Dam. Flow hydrographs showing peak discharge for ranging from 5 ARI to 100,000 ARI and the Probable Maximum Flood (PMF), illustrating the increase in peak flow with higher ARIs and extreme events. https://doi.org/10.1371/journal.pone.0311181.g019 PLOS ONE Climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0311181 February 27, 2025 26 / 32

Fig 21. RCP8.5 mid century peak inflow design flood at Batu Dam. Flow hydrographs showing peak discharge for ranging from 5 ARI to 100,000 ARI and the Probable Maximum Flood (PMF), illustrating the increase in peak flow with higher ARIs and extreme events. https://doi.org/10.1371/journal.pone.0311181.g021 Fig 22. RCP4.5 mid century peak inflow design flood at Batu Dam. Flow hydrographs showing peak discharge for ranging from 5 ARI to 100,000 ARI and the Probable Maximum Flood (PMF), illustrating the increase in peak flow with higher ARIs and extreme events. https://doi.org/10.1371/journal.pone.0311181.g022 PLOS ONE Climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0311181 February 27, 2025 27 / 32

Fig 23. RCP6.0 mid century peak inflow design flood at Batu Dam. Flow hydrographs showing peak discharge for ranging from 5 ARI to 100,000 ARI and the Probable Maximum Flood (PMF), illustrating the increase in peak flow with higher ARIs and extreme events. https://doi.org/10.1371/journal.pone.0311181.g023 Fig 24. RCP8.5 mid century peak inflow design flood at Batu Dam. Flow hydrographs showing peak discharge for ranging from 5 ARI to 100,000 ARI and the Probable Maximum Flood (PMF), illustrating the increase in peak flow with higher ARIs and extreme events. https://doi.org/10.1371/journal.pone.0311181.g024 PLOS ONE Climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0311181 February 27, 2025 28 / 32

Fig 25. Maximum reservoir level based on inflow for PMF and return period. Projected flood levels between 1 and 100000 Average Recurrence Intervals (ARI) under three emission scenarios: RCP4.5, RCP6.0, and RCP8.5 across different time periods; the historical baseline from 1975–2019 is compared to early-century (2020–2046), mid-century (2047–2073), and late-century (2074–2100) projections. https://doi.org/10.1371/journal.pone.0311181.g025 Fig 26. Inflow for PMF and return period between 1 and 100 000-years. hydrograph at (a) Early Century (2020– 2046), (b) Mid Century (2047–2073), and (c) Late Century (2074–2100) under different climate scenarios. The upper line indicates inflows exceeding the dam crest level. In the historical period from 1975 to 2019, the water levels have consistently remained below the crest level of embankment dams, indicating no overtopping risk during this timeframe. This observation aligns with the stability and performance of existing dam structures under historical climate conditions. The absence of overtopping incidents suggests that the design and operational protocols in place were effective for the climatic conditions experienced during this period. https://doi.org/10.1371/journal.pone.0311181.g026 PLOS ONE Climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0311181 February 27, 2025 29 / 32

Acknowledgments The authors would like to thank the Department of Irrigation and Drainage (DID), National Water, Research Institute of Malaysia (NAHRIM), and Universiti Tenaga Nasional for sup- porting the research work. Author Contributions Conceptualization: Wan Noorul Hafilah Wan Ariffin, Lariyah Mohd Sidek. Data curation: Hazri Mohd Khambali, Muhammad Izzat Azhar Khebir, Ali Najah Ahmed. Formal analysis: Wan Noorul Hafilah Wan Ariffin. Funding acquisition: Lariyah Mohd Sidek. Investigation: Wan Noorul Hafilah Wan Ariffin, M. Torres Adrian, Muhammad Izzat Azhar Khebir. Methodology: Wan Noorul Hafilah Wan Ariffin, Hidayah Basri. Project administration: Hazri Mohd Khambali. Resources: Noorhayati Idros, Noor Hisham Abd Ghani, Hazri Mohd Khambali. Software: M. Torres Adrian, Siti Mariam Allias Omar. Supervision: Lariyah Mohd Sidek, Hidayah Basri. Validation: Hidayah Basri, Noor Hisham Abd Ghani, Siti Mariam Allias Omar, Muhammad Izzat Azhar Khebir. Visualization: Noorhayati Idros, M. Torres Adrian, Noor Hisham Abd Ghani, Ali Najah Ahmed. Writing – original draft: Siti Mariam Allias Omar. Writing – review & editing: Wan Noorul Hafilah Wan Ariffin, Noorhayati Idros, Ali Najah Ahmed. References 1. Zhang S., Hou W., Yin J., & Lin Z. (2022). A Review of Research and Practice on the Theory and Tech- nology of Reservoir Dam Risk Assessment. Sustainability, 14, 14984. https://doi.org/10.3390/ su142214984 2. ICOLD (2011). Definition of a Large Dam. Commission International des Grands Barrages, International

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