Regmi et al. (2025) Enhancing hydropower resilience through dynamic rule curve modifications under climate change in the Sunkoshi multipurpose scheme, Nepal

Identification

• Journal: Scientific Reports
• Year: 2025
• Date: 2025-10-09
• Authors: Ram Krishna Regmi, AK Shrestha, Vishan Dahal, Subash Kunwar
• DOI: 10.1038/s41598-025-19252-8

Research Groups

• Department of Civil Engineering, Institute of Engineering, Tribhuvan University, Pulchowk Campus, Patan, Nepal

Short Summary

This study assesses climate change impacts on the Sunkoshi River Basin and proposes dynamic rule curve modifications for four hydropower projects to optimize reservoir operations. The adaptive strategy significantly increases average yearly energy generation, with up to 71.26% for Sunkoshi No.1, enhancing hydropower resilience under future climate scenarios.

Objective

• To examine climate variable alterations using CMIP6 GCMs under SSP245 and SSP585 scenarios in the Sunkoshi River Basin.
• To evaluate the impact of these alterations on the hydrological regime and hydropower generation of four planned reservoir projects (Sunkoshi No.1, No.2, No.3, and Dudhkoshi).
• To propose dynamic rule curves for cascading reservoirs in the Sunkoshi Basin to ensure sustainable and efficient hydropower generation under future climate conditions.

Study Configuration

• Spatial Scale: Sunkoshi River Basin, a transboundary basin in Nepal and Tibet (China), covering approximately 18,140 km² with elevations from 111 meters to 8,777 meters above sea level. The study focuses on four planned cascading hydropower projects: Sunkoshi No.1, Sunkoshi No.2, Sunkoshi No.3, and Dudhkoshi.
• Temporal Scale: Historical (1990–2014), baseline (1993–2014), and future projections (2015–2100) analyzed in three timeframes: 2030s (2015–2039), 2060s (2040–2064), and 2080s (2065–2089). Daily time step for simulations.

Methodology and Data

• Models used: CMIP6 General Circulation Models (ACCESS-CM2, BCC-CSM2-MR, CanESM5, EC-Earth3, MPI-ESM1-2-HR, MPI-ESM1-2-LR, NorESM2-MM), CMhyd (bias correction), Soil and Water Assessment Tool (SWAT) / ArcSWAT 10.8, SWAT-CUP (SUFI-2 algorithm for calibration/validation), Hydrologic Engineering Center-Reservoir System Simulation (HEC-ResSim) 3.3.
• Data sources:
  • Observed Hydro-meteorological: Daily hydrological data (1990–2014) from DHM, Nepal (Pachuwarghat, Rabuwa Bazar, Hampachuwar); daily meteorological data (1990–2014) from 13 stations (DHM, Nepal); APHRODITE precipitation data; daily maximum/minimum temperature from Dhulikhel, Jiri, Okhaldhunga.
  • Geospatial: NASA Digital Elevation Model (NASADEM); Land Use and Land Cover (LULC) map (2010) from ICIMOD; Soil map from FAO.
  • Climate Projections: Bias-corrected CMIP6 GCM data (1951–2100) for SSP245 and SSP585 scenarios (Mishra et al., 2020).
  • Reservoir System: Physical and operational data from Nepal Electricity Authority (NEA) reports and prior studies.

Main Results

• Climate Projections:
  • Precipitation: Projected irregular trends. Under SSP245, September shows a maximum increase of 33.81% (2030s), while January shows a maximum decrease of 36.02% (2080s). Under SSP585, May shows a maximum increase of 50.40% (2080s), and January a maximum decrease of 33.75% (2080s). Seasonal analysis indicates increases in pre-monsoon, monsoon, and post-monsoon precipitation (larger under SSP585 in 2080s), but consistent declines in winter precipitation.
  • Maximum Temperature: Anticipated to rise by 1–3 °C under SSP245 and 1–10 °C under SSP585, with the highest increases observed in the 2080s and most significantly during winter seasons.
  • Minimum Temperature: Projected to increase consistently across all decades, ranging from 0.20 °C to 4.83 °C under SSP245 and 0.18 °C to 8.10 °C under SSP585, with a significant rise during the monsoon season.
• Hydrological Analysis:
  • The SWAT model demonstrated good performance with R² > 0.5, NSE > 0.5, and PBIAS < ±25% for calibration and validation periods.
  • Future discharge at Sunkoshi No.3 is projected to increase from March to November (peaking in June) under SSP245, with decreases from November to December (maximum in January 2080s). Under SSP585, discharge generally increases across all months (peaking in June), with only January 2030s showing a decrease, while 2060s and 2080s show consistent increases.
• Energy Generation Projections:
  • Baseline average yearly energy generation ranged from 1648.88 GWh/yr (Sunkoshi No.3) to 2963.55 GWh/yr (Dudhkoshi).
  • Under SSP245 (2080s), generation is projected to reach 3258.38 GWh/yr (Sunkoshi No.1), 3082.27 GWh/yr (Sunkoshi No.2), 1838.91 GWh/yr (Sunkoshi No.3), and 3186.79 GWh/yr (Dudhkoshi).
  • Under SSP585 (2080s), generation is projected to reach 4072.33 GWh/yr (Sunkoshi No.1), 3852.88 GWh/yr (Sunkoshi No.2), 2067.69 GWh/yr (Sunkoshi No.3), and 3273.94 GWh/yr (Dudhkoshi). Sunkoshi No.1 shows a remarkable 70.15% increase in generation during the 2080s under SSP585.
• Dynamic Rule Curve Modifications:
  • Six different rule curves were proposed, with Rule Curve 06 identified as the most effective for maximizing energy generation across future periods.
  • Implementation of dynamic rule curves resulted in significant increases in average yearly energy generation compared to baseline:
    • Sunkoshi No.3: 7% to 25.5% increase.
    • Sunkoshi No.2: 19% to 61.07% increase.
    • Sunkoshi No.1: 23% to 71.26% increase.
    • Dudhkoshi: 4% to 10.50% increase.

Contributions

• Integrates CMIP6 GCMs, SWAT, and HEC-ResSim in a novel framework to assess climate change impacts on hydropower operations in Nepal.
• Proposes and evaluates dynamic rule curve modifications as an adaptive strategy for cascading reservoirs, bridging hydrological modeling with real-time hydropower management.
• Offers a new operational framework for climate adaptation in complex multi-reservoir systems, moving beyond impact assessment to provide concrete adaptive strategies.

Funding

No specific funding projects or reference codes for this research were listed in the paper.

Citation

@article{Regmi2025Enhancing,
  author = {Regmi, Ram Krishna and Shrestha, AK and Dahal, Vishan and Kunwar, Subash},
  title = {Enhancing hydropower resilience through dynamic rule curve modifications under climate change in the Sunkoshi multipurpose scheme, Nepal},
  journal = {Scientific Reports},
  year = {2025},
  doi = {10.1038/s41598-025-19252-8},
  url = {https://doi.org/10.1038/s41598-025-19252-8}
}