Ho et al. (2025) The impact of climate change on dam overtopping floods in Australia

Identification

• Journal: Hydrology and earth system sciences
• Year: 2025
• Date: 2025-11-03
• Authors: Michelle Ho, Declan O’Shea, Conrad Wasko, Rory Nathan, Ashish Sharma
• DOI: 10.5194/hess-29-5851-2025

Research Groups

• Department of Infrastructure Engineering, The University of Melbourne
• HARC-Hydrology and Risk Consulting
• School of Civil Engineering, The University of Sydney
• School of Civil and Environmental Engineering, The University of New South Wales

Short Summary

This study projects changes in the exceedance probabilities of dam overtopping floods for 18 large Australian dams under various global warming scenarios. It finds that under 4 °C of global warming, the probability of overtopping floods increases by 2.4–17 times compared to historical conditions, primarily driven by increases in rainfall depth.

Objective

• To project changes in the exceedance probabilities of dam overtopping floods for 18 large dams in Australia under a range of global warming assumptions.
• To explicitly consider the impacts of climate change on rainfall depth, rainfall temporal patterns, and rainfall losses resulting from changes in antecedent catchment wetness.

Study Configuration

• Spatial Scale: 18 large water-supply dams across Australia, with wall heights ranging from 16–166 m and catchments from 28–15 300 km². These dams are located across arid, temperate, and tropical climate zones, and five Probable Maximum Precipitation (PMP) zones.
• Temporal Scale: Historical baseline period of 1961–1990; future projections for global warming increments of 1–5 °C (relative to the 1961–1990 baseline), approximating conditions towards the end of the 21st century under high emissions scenarios.

Methodology and Data

• Models used:
  • Event-based flood modelling within a Monte Carlo framework.
  • RORB (Runoff Routing Program) emulated in the R software environment (R2ORB).
  • Initial Loss Continuing Loss (ILCL) model for rainfall partitioning.
  • Non-linear storage routing power function for streamflow and reservoir routing.
• Data sources:
  • Rates of change (uplift factors) for rainfall depth, temporal patterns, and rainfall losses derived from systematic reviews and meta-analyses of climate change impacts (Wasko et al., 2024a, b; Visser et al., 2022, 2023; Ho et al., 2023).
  • Historical design information from Australian Rainfall and Runoff (Ball et al., 2019).
  • PMP zone-specific temporal patterns (Bureau of Meteorology, 2006; Green et al., 2005; Nathan, 1992; Walland et al., 2003).
  • Empirical distribution for initial rainfall losses (Hill et al., 2014).
  • IPCC AR6 Shared Socioeconomic Pathway (SSP) global mean surface temperature change projections (Fyfe et al., 2021; IPCC, 2021b) for contextualizing global warming scenarios.
  • Catchment models and dam operational data provided by dam owners.

Main Results

• Under 4 °C of global warming, the probability of overtopping floods for the 18 investigated dams increases by 2.4–17 times (with a median of 5.5) compared to historical conditions (1961–1990 baseline).
• Current global warming (approximately 1 °C above the 1961–1990 baseline) has already more than doubled the overtopping probability for two of the 18 dams.
• Increases in rainfall depth had the largest impact on overtopping probability for all 18 dams, increasing it by approximately an order of magnitude under 4 °C of global warming.
• Changes in storm temporal patterns had marginal impacts, with the direction and magnitude of change being catchment-specific and not necessarily unidirectional with increased global temperature.
• Changes in rainfall losses slightly decreased the probability of overtopping floods across all locations, dampening the impact of increased rainfall intensity.
• The combined impacts of all three flood drivers consistently showed an overall increase in overtopping probability.
• It is currently not possible to provide general heuristics for estimating changes in flood frequency based on dam-specific attributes (e.g., location, climate zone, or catchment/dam size); site-specific assessments are required.

Contributions

• Presents the first assessment quantifying changes in flood-induced dam overtopping probabilities under climate change for a broad sample of Australian dams.
• Explicitly considers the combined and individual impacts of climate change on rainfall depth, storm temporal patterns, and rainfall losses in a practical, industry-adoptable manner.
• Provides a tractable approach for estimating extreme flood frequency and dam overtopping probability under climate change that aligns with methods widely used by practitioners, making it feasible for global adoption.
• Conditions the assessment on global mean temperature increases, allowing results to be translated to various climate change scenarios and future time horizons without requiring complex climate model evaluations.

Funding

• Australian Research Council (ARC) Discovery Projects (DP200101326)
• Australian Research Council (ARC) (DE210100479)
• Industry support from Queensland Department of Natural Resources, Mines and Energy, Hydro Tasmania, Melbourne Water Corporation, Murray-Darling Basin Authority, Seqwater, Snowy Hydro, Sunwater, West Australia Water Corporation, and WaterNSW.
• Australian Government Research Training Program Scholarship (Declan O’Shea)
• University of Melbourne Lochrie Engineering Scholarship (Declan O’Shea)
• University of Sydney Horizon Fellowship (Conrad Wasko)

Citation

@article{Ho2025impact,
  author = {Ho, Michelle and O’Shea, Declan and Wasko, Conrad and Nathan, Rory and Sharma, Ashish},
  title = {The impact of climate change on dam overtopping floods in Australia},
  journal = {Hydrology and earth system sciences},
  year = {2025},
  doi = {10.5194/hess-29-5851-2025},
  url = {https://doi.org/10.5194/hess-29-5851-2025}
}