Li et al. (2025) Multi-objective optimization of seasonal emergency storage in cascade reservoirs for enhanced drought resilience and hydropower synergy

Identification

• Journal: Journal of Water and Climate Change
• Year: 2025
• Date: 2025-10-03
• Authors: Shufei Li, Jun Xia, Yanlai Zhou, Chong‐Yu Xu, Fi-John Chang
• DOI: 10.2166/wcc.2025.816

Research Groups

• State Key Laboratory of Water Resources Engineering and Management, Wuhan University, Wuhan, China
• Department of Geosciences, University of Oslo, Oslo, Norway
• Department of Bioenvironmental Systems Engineering, National Taiwan University, Taipei, Taiwan

Short Summary

This study presents a multi-objective optimization framework for enhancing seasonal emergency storage capacity (SESC) in cascade reservoirs to simultaneously improve hydropower generation (HG) and drought resilience. Applied to a five-reservoir cascade on the Yangtze River, the model outperforms the standard operation policy (SOP), yielding an 8.7% increase in hydropower output, a 45.5% reduction in river drought duration, and a 4.5% improvement in low-flow conditions.

Objective

• To develop a multi-objective optimization framework for seasonal emergency storage capacity (SESC) in cascade reservoirs to enhance drought resilience and hydropower generation synergy, considering spatiotemporal drought variability and complex hydraulic interconnections.

Study Configuration

• Spatial Scale: Five-reservoir cascade system (Wu-Dong-De, Bai-He-Tan, Xi-Luo-Du, Xiang-Jia-Ba, and Three Gorges Reservoirs) in the upper Yangtze River basin, China.
• Temporal Scale: Drawdown period from December 1st to June 10th, analyzed using historical data from 1966 to 2022. The dry season is divided into pre-drought (December), main drought (January-April), and post-drought (May) sub-seasons.

Methodology and Data

• Models used:
  • Month-by-month moving calculation method (MMCM) for determining Seasonal Emergency Storage Capacity (SESC).
  • Standardized Runoff Index (SRI) and Standardized Precipitation Evapotranspiration Index (SPEI) for drought identification.
  • Non-dominated Sorting Genetic Algorithm-II (NSGA-II) for multi-objective optimization of cascade reservoir drawdown operations.
  • Combinative Distance-based Assessment (CODAS) method for multi-criteria decision-making (MCDM) to select the optimal scheme from Pareto solutions.
• Data sources:
  • Historical flow data from hydrological stations (54,790 records from 1966 to 2022).
  • Characteristic parameters of the five cascade reservoirs (e.g., normal water level, flood-limited water level, dead water level, total storage capacity, installed power output, maximal/minimal outflow).
  • Inflow processes for representative hydrological scenarios (wet, normal, dry, and extremely dry years, e.g., 1966 for P=95%).

Main Results

• The multi-objective optimization framework, incorporating SESC, significantly outperforms the Standard Operation Policy (SOP) across various hydrological scenarios.
• A nonlinear competitive relationship exists between hydropower generation (HG) and river drought risk (RDR); maximizing HG tends to increase RDR, especially during pre- and main drought seasons.
• The optimal operational scheme, selected by the CODAS method, demonstrates substantial improvements compared to the SOP:
  • Hydropower output increased by 6.2–10.7% (7.28–9.89 TWh annually), with greater gains under drier conditions.
  • River Drought Risk (RDR) reduced by 3.1–19.3%.
  • Time length of river water shortages (LWS) decreased by 42.9–67.3%.
  • Minimum water release increased by 4.5% (improving low-flow conditions).
• The optimized strategy involves upstream reservoirs releasing water first while downstream reservoirs activate emergency storage capacity (ESC) below the SESC during extreme drought years, leveraging seasonal inflow characteristics.

Contributions

• Introduces a novel month-by-month moving calculation method (MMCM) to determine Seasonal Emergency Storage Capacity (SESC), explicitly accounting for drought seasonality and improving water resource allocation accuracy.
• Develops an NSGA-II-based multi-objective optimization model specifically tailored for cascade reservoir drawdown operations, integrating complex hydraulic interconnections and SESC constraints.
• Employs the CODAS method for rigorous multi-criteria decision-making, enabling the identification of the most effective drawdown strategy that balances hydropower generation and drought resilience.
• Provides a robust framework for climate-adaptive water resource management, offering operational synergies and data-driven strategies for sustainable hydropower development and drought defense in cascade reservoir systems.

Funding

• National Key Research and Development Program of China (No. 2024YFC3212700)
• Hubei Provincial Natural Science Foundation of China (2025AFA023)

Citation

@article{Li2025Multiobjective,
  author = {Li, Shufei and Xia, Jun and Zhou, Yanlai and Xu, Chong‐Yu and Chang, Fi-John},
  title = {Multi-objective optimization of seasonal emergency storage in cascade reservoirs for enhanced drought resilience and hydropower synergy},
  journal = {Journal of Water and Climate Change},
  year = {2025},
  doi = {10.2166/wcc.2025.816},
  url = {https://doi.org/10.2166/wcc.2025.816}
}