Shen et al. (2025) Two recent mega dams reshape Yangtze river hydrology with comparable impact to Three Gorges Dam

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2025
• Date: 2025-12-01
• Authors: Youjiang Shen, Dai Yamazaki, Yadu Pokhrel, Gang Zhao, Huy Dang
• DOI: 10.1016/j.ejrh.2025.103017

Research Groups

• Global Hydrological Prediction Centre, Institute of Industrial Science, The University of Tokyo, Tokyo, Japan
• Department of Civil Engineering, Graduate School of Engineering, The University of Tokyo, Tokyo, Japan
• Department of Civil and Environmental Engineering, Michigan State University, East Lansing, MI, USA
• Department of Transdisciplinary Science and Engineering, Institute of Science Tokyo, Tokyo, Japan

Short Summary

This study quantifies the hydrological impacts of two recently completed mega-dams (Wudongde and Baihetan, 2MDs) upstream of the Three Gorges Dam (TGD) in the Yangtze River basin, revealing that their collective effects on water levels and flood peak reductions are comparable to those of the TGD, necessitating coordinated basin-wide management.

Objective

• To provide a timely assessment of the impacts of two newly completed mega-dams (Wudongde and Baihetan, 2MDs) on Yangtze River hydrology, including their collective effects with the Three Gorges Dam (TGD), by quantifying their contribution to recent water level changes and exploring their impacts under varying hydrological conditions using a satellite-based target storage scheme.

Study Configuration

• Spatial Scale: Yangtze River basin, China. Model resolution of 3 arcminutes (approximately 5 kilometers).
• Temporal Scale: Simulation period from 1981 to 2023, with a focus on recent impacts (2022–2023 drought) and long-term potential hydrological alterations.

Methodology and Data

• Models used: CaMa-Flood river model, enhanced with a satellite-based target storage (SBTS) scheme for simulating reservoir operations.
• Data sources:
  • Runoff forcings: ERA5 runoff dataset.
  • Baseline topography: MERIT Hydro.
  • Dam attributes: GRanD database and parameters for 121 dams.
  • Validation data: Hydroweb satellite river water level data, in-situ streamflow and water level data from hydrologic stations, and in-situ reservoir operation data.

Main Results

• During the 2022–2023 drought, the 2MDs reduced high water levels by 1.2 %–6.0 % and increased low water levels by 11.0 %–36.2 % across the basin compared to simulations without dams.
• The 2MDs showed dual impacts, intensifying water stress during reservoir refill (September-October 2022) while alleviating it in dry seasons (November 2022-April 2023) through increased releases.
• Long-term simulations reveal that 2MDs achieve flood peak reductions (e.g., 3.3 % at Yichang, 1.7 % at Hankou) that are remarkably comparable to those of the TGD (e.g., 10.4 % at Yichang, 1.9 % at Hankou).
• The combined effect of TGD and 2MDs contributes approximately half of the total dam-induced flood risk mitigation at Yichang station.
• Under long-term mean climatological conditions, 2MDs reduce high water levels by 2.7 % and water level amplitude by 9.5 %.
• The TGD demonstrates a stronger capability in regulating seasonal flow variations, particularly in the middle and lower reaches, compared to the 2MDs.

Contributions

• Provides the first timely assessment quantifying the hydrological impacts of the recently completed Wudongde and Baihetan mega-dams (2MDs) in the Yangtze River basin, addressing a critical knowledge gap.
• Demonstrates that the 2MDs have impacts on water levels and flood peak reductions comparable to the Three Gorges Dam (TGD), highlighting their significant and far-reaching influence on the basin's hydrology.
• Utilizes and validates a novel satellite-based target storage (SBTS) scheme within the CaMa-Flood model to simulate dam operations without requiring in-situ operational data, enabling rapid assessment of newly built dams.
• Reveals complex interactions between 2MDs and extreme hydrological events (e.g., the 2022–2023 drought), showing dual impacts of intensifying water stress during refill and alleviating it in dry seasons.
• Underscores the urgent need for cohesive, basin-wide operational strategies for all mega-dams to manage water storage conflicts and optimize collective benefits, particularly under intensifying climate extremes.

Funding

• Japan Society for the Promotion of Science (JSPS) under KAKENHI 21H05002 and KAKENHI 24KJ0780.
• MEXT "Program for the advanced studies of climate change projection" (SENTAN: JPMXD0722680395).

Citation

@article{Shen2025Two,
  author = {Shen, Youjiang and Yamazaki, Dai and Pokhrel, Yadu and Zhao, Gang and Dang, Huy},
  title = {Two recent mega dams reshape Yangtze river hydrology with comparable impact to Three Gorges Dam},
  journal = {Journal of Hydrology Regional Studies},
  year = {2025},
  doi = {10.1016/j.ejrh.2025.103017},
  url = {https://doi.org/10.1016/j.ejrh.2025.103017}
}