Yang et al. (2026) Improved Comprehensive Flood Risk Index Method and Multi-Scenario Flood Simulation for Downstream Area of the Reservoir

Identification

• Journal: Water Resources Management
• Year: 2026
• Date: 2026-01-01
• Authors: Nijuan Yang, Ting Zhang, Jie Li, Ping Feng
• DOI: 10.1007/s11269-025-04370-9

Research Groups

• State Key Laboratory of Hydraulic Engineering Intelligent Construction and Operation, Tianjin University, Tianjin, China

Short Summary

This study developed an improved comprehensive flood risk index method integrating flood probability, hazard, and socioeconomic vulnerability, and applied it with multi-scenario flood simulations to assess flood risk downstream of Fenglongwan Reservoir. The research revealed that dam-break events cause significantly higher economic losses (4–10 times) and expand high-risk areas compared to emergency flood discharges, with agricultural losses dominating.

Objective

• To employ the Integrated Flood Modeling System (IFMS) and a flood loss assessment model to simulate flood processes and quantify losses under six flooding scenarios, including emergency flood discharge and dam-break events across design, check, and overtopping flood magnitudes.
• To develop an improved comprehensive flood risk index model to characterize flood risk zoning under both emergency flood discharge and dam-break events.
• To provide a theoretical basis and robust guidance for reservoir flood safety management and risk mitigation strategies.

Study Configuration

• Spatial Scale: Downstream area of Fenglongwan Reservoir in Xundian County, Yunnan Province, China. The reservoir watershed covers an area of 957 square kilometers. Geospatial data resolutions include 5-meter DEMs and 1-meter land cover data.
• Temporal Scale: Simulation of flood processes for six scenarios (emergency flood discharge and dam-break events under design, check, and overtopping flood magnitudes). Flood durations ranged from 32.20 to 49.96 hours. Historical flood archives from 1978–2020 were used for vulnerability assessment.

Methodology and Data

• Models used:
  • Integrated Flood Modeling System (IFMS) (a multi-dimensional flood analysis platform coupling 1D river network, 2D hydrodynamic, and urban drainage models).
  • Flood Loss Assessment Model (developed by China Institute of Water Resources and Hydropower Research, based on GIS platform).
  • Improved Comprehensive Flood Risk Index Method (integrating flood hazard factors: inundation depth, flow velocity, inundation duration; and flood vulnerability factors: population exposure density, cultivated land vulnerability, slope, and GDP density).
• Data sources:
  • Geospatial data: 1:2000-scale topographic maps (processed into 5-meter resolution DEMs), 1-meter resolution land cover data (9 categories), 5-meter × 5-meter slope data.
  • Socio-economic data: Population and GDP data from WorldPop platform, Yunnan Statistical Yearbook 2024, Xundian County Statistical Yearbook 2024, and Socioeconomic Statistical Bulletins 2024.
  • Hydrological records: Monitoring station data (coordinates, discharge, precipitation records) from Yunnan Hydrology Bureau, historical flood archives, Flood Control Plan for Fenglongwan Reservoir in Xundian, Kunming, Yunnan Province (2022), and Hydrological Analysis Results of Flood-Drought Disasters in Xundian County (2022).

Main Results

• The IFMS model accurately simulated flood dynamics, with a 6.1% peak discharge deviation at Qixingqiao Station and water level errors of 7–14 centimeters at three control sections. Hydrograph agreement was high (R² = 0.86–0.92) with low bias (PBIAS = 0.17–3.7%).
• Dam-break scenarios generated significantly larger peak discharges (e.g., 10,994 cubic meters per second for overtopping flood) and shorter flood arrival times compared to emergency flood discharge scenarios (e.g., 946 cubic meters per second for overtopping flood).
• Across the six scenarios, inundation areas ranged from 8.22 to 36.01 square kilometers, mean flow velocities from 1.39 to 4.44 meters per second, and mean inundation durations from 32.20 to 49.96 hours. The dam-break overtopping flood (DOF) scenario showed catastrophic characteristics, with 33% of the inundated region experiencing depths greater than 3 meters.
• Total economic losses ranged from 0.79 billion Chinese Yuan (CNY) for emergency flood discharge to 38.96 billion CNY for dam-break scenarios, with agricultural loss comprising the overwhelming majority (82–93%). Dam-break scenarios incurred 4–10 times higher economic losses than emergency flood discharge scenarios.
• Low-risk areas predominated in both events (63.07% for emergency flood discharge and 56.55% for dam-break). However, dam-break events substantially increased high-risk (from 1.67 square kilometers to 5.10 square kilometers) and extremely high-risk zones (from 0.13 square kilometers to 2.89 square kilometers). High-risk zones clustered in river-adjacent agricultural and densely populated regions, with Jiangwai Village and Lawei Village exhibiting high risk in the dam-break event.
• The improved comprehensive flood risk index method, by integrating vulnerability, reduced low-risk areas by 35.9% (emergency discharge) and 32.4% (dam-break flood) compared to the original method, reclassifying these zones to higher risk levels and providing a more accurate risk assessment.

Contributions

• Proposed and validated an improved comprehensive flood risk index method that integrates flood probability, multi-dimensional hazard factors (inundation depth, flow velocity, duration), and socioeconomic vulnerability factors (population density, cultivated land ratio, slope, GDP density).
• Conducted a comprehensive multi-scenario flood simulation for a reservoir downstream area, covering both emergency flood discharge and dam-break events under varying flood magnitudes (design, check, overtopping).
• Quantified and compared the socioeconomic impacts and economic losses across these diverse flood scenarios, highlighting the disproportionate impact of dam-break events and the dominance of agricultural losses.
• Established a robust framework for reservoir safety management and targeted flood control planning, demonstrating the critical importance of incorporating socioeconomic vulnerability for more accurate and actionable flood risk assessment.

Funding

• Key Technologies Research and Development Program (2023YFC3006501, 2023YFC3006503)
• National Natural Science Foundation of China (No. 52579014, 52279022)
• Open Research Fund of Key Laboratory of Water Safety for Beijing-Tianjin-Hebei Region of Ministry of Water Resources (No. IWHR-JJJ-202405)

Citation

@article{Yang2026Improved,
  author = {Yang, Nijuan and Zhang, Ting and Li, Jie and Feng, Ping},
  title = {Improved Comprehensive Flood Risk Index Method and Multi-Scenario Flood Simulation for Downstream Area of the Reservoir},
  journal = {Water Resources Management},
  year = {2026},
  doi = {10.1007/s11269-025-04370-9},
  url = {https://doi.org/10.1007/s11269-025-04370-9}
}