Pokhrel et al. (2026) Upstream hydrology and the importance of snowmelt in buffering droughts in the Karnali basin in Nepal

Identification

• Journal: Frontiers in Water
• Year: 2026
• Date: 2026-02-24
• Authors: Pranisha Pokhrel, Jasper Griffioen, Thom A. Bogaard, Philip Kraaijenbrink, Joel Fiddes, Walter Immerzeel
• DOI: 10.3389/frwa.2025.1720178

Research Groups

• Copernicus Institute of Sustainable Development, Utrecht University, Utrecht, Netherlands
• TNO Geological Survey of the Netherlands, Utrecht, Netherlands
• Department Water Management, Delft University of Technology, Delft, Netherlands
• Department of Physical Geography, Utrecht University, Utrecht, Netherlands
• WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland

Short Summary

This study quantifies the water balance and drought buffering capacity in Nepal's Karnali basin using a distributed hydrological model, revealing that snowmelt contributes 24% of total discharge and significantly buffers hydrological droughts for up to 6 months.

Objective

• Quantify a benchmark water balance and assess hydrological shifts in the Karnali River basin using a high-resolution distributed hydrological model.
• Evaluate drought response and the critical role of snow storage in buffering droughts in the Karnali River basin.
• Investigate the propagation of meteorological drought to hydrological droughts and explore how snow storage alters their onset and recovery.

Study Configuration

• Spatial Scale: Karnali River basin (45,496 km² upstream of Chisapani). Model resolution: 500 meters. Model domain: 86,758 km².
• Temporal Scale: Period: 1991–2022 (32 years). Temporal resolution: daily.

Methodology and Data

• Models used: Spatial Processes in Hydrology (SPHY) model (version 3.0).
• Data sources:
  • Digital Elevation Model (DEM): ALOS Global Digital Surface Model (AW3D30) (30 m resolution, resampled to 500 m).
  • Meteorological forcing: ERA5 reanalysis (hourly, bias-corrected and downscaled to 500 m daily fields).
  • Glacier outlines: Randolph Glacier Inventory 6 (RGI6).
  • Land cover: European Space Agency’s Climate Change Initiative (ESA CCI) (300 m resolution, reclassified and resampled to 500 m).
  • Soil hydraulic properties: global HiHydroSoil v2.0 database (250 m resolution, resampled to 500 m).
  • Observed discharge data: Department of Hydrology and Meteorology of Nepal (DHM Nepal) from three stations.
  • Observed meteorological data: 10 stations from DHM Nepal for comparison.

Main Results

• The SPHY model showed good performance, with Kling-Gupta efficiency (KGE) ranging from 0.79 to 0.84 and a bias between -3.33% and 10.70% during calibration.
• The overall Karnali basin receives an annual average precipitation of 1,485 mm/year, with an actual evapotranspiration of 574 mm/year (39% of precipitation) and an average discharge of 914 mm/year (1,291 m³/s).
• Discharge composition for the overall Karnali basin is 40% rain runoff, 35% baseflow, 24% snowmelt, and 0.8% glacier melt.
• Snowmelt contribution to monthly average discharge ranges from 26% in January to a peak of 74% in May, significantly influencing water availability during spring and early summer.
• Monthly streamflow anomalies have increased over the last decade, indicating a more variable and less predictable streamflow regime.
• Meteorological droughts generally propagate to hydrological droughts with a lag time of less than 1 month, showing a high correlation (0.74 for 3-month indices). The average duration of a hydrological drought period is approximately 6 months.
• Initial snow storage substantially influences discharge variability for several months, with an impact comparable to meteorological variability. This buffering role is more pronounced at higher elevations and decreases downstream.

Contributions

• Bridges the scale gap in hydrological studies in High Mountain Asia by providing a high-resolution, distributed hydrological model application for the medium-scale Karnali River basin.
• Quantifies a detailed benchmark water balance and the specific contributions of different flow components (rain runoff, baseflow, snowmelt, glacier melt) for the Karnali basin.
• Provides a comprehensive assessment of hydrological shifts and drought response, highlighting the critical role of snowmelt and initial snow storage in buffering droughts and influencing streamflow variability for up to 6 months.
• Demonstrates the decreasing natural buffering capacity downstream, emphasizing the need for integrated upstream-downstream water management strategies to enhance drought resilience.

Funding

• Dutch Research Council NWO, with co-financing partners Planet, Rotterdam Zoo, Himalayan Tiger Foundation, and Practical Action (Grant No. NWA.1292.19.146).
• Swiss National Science Foundation (Grant No. 179130) for co-author J. Fiddes.

Citation

@article{Pokhrel2026Upstream,
  author = {Pokhrel, Pranisha and Griffioen, Jasper and Bogaard, Thom A. and Kraaijenbrink, Philip and Fiddes, Joel and Immerzeel, Walter},
  title = {Upstream hydrology and the importance of snowmelt in buffering droughts in the Karnali basin in Nepal},
  journal = {Frontiers in Water},
  year = {2026},
  doi = {10.3389/frwa.2025.1720178},
  url = {https://doi.org/10.3389/frwa.2025.1720178}
}