Kumar et al. (2025) Impact of climate change on flood properties in a mountainous catchment of Nepal Himalayas

Identification

• Journal: Natural Hazards
• Year: 2025
• Date: 2025-12-26
• Authors: Sanjay Kumar, Pankaj Dey, Brijesh Kumar Yadav
• DOI: 10.1007/s11069-025-07775-2

Research Groups

• Department of Hydrology, Indian Institute of Technology, Roorkee, Uttrakhand, India
• College of Forestry, Banda University of Agriculture and Technology, Banda, Uttar Pradesh, India
• Mehta Family School of Sustainability, Indian Institute of Technology, Indore, India

Short Summary

This study assesses the impact of climate change on flood properties (peak, volume, duration, seasonality, and sensitivity) in the West Seti River Basin, Nepal Himalayas, finding increased flood peaks, decreased durations, delayed timing, and higher sensitivity to precipitation in future scenarios.

Objective

• To explore the changes in the distribution of flood hydrograph properties such as flood peaks, flood volumes, and flood duration.
• To investigate the changes in the flood seasonality and timing of annual maximum floods.
• To assess the sensitivity of flood peaks and flood volumes to changing precipitation and temperature patterns.

Study Configuration

• Spatial Scale: West Seti River Basin (WSRB), Nepal Himalayas, covering approximately 7368.26 square kilometers. The elevation ranges from 335 meters to 7013 meters above mean sea level. Analysis was conducted at two gauging stations: Gopaghat and Banga.
• Temporal Scale:
  • Historical period: 1986–2019 (for flood properties analysis, streamflow at Gopaghat), 1963–2019 (streamflow at Banga).
  • Future period: 2031–2100 (for flood properties analysis), 2015–2100 (CMIP6 projections).
  • Rainfall data: 1970–2022 (some stations), 1980–1999 (some stations), 2000–2022 (all 29 stations).
  • Temperature data: 1980–2022 (5 stations).
  • ERA5 reanalysis: 1979–2019.

Methodology and Data

• Models used:
  • Hydrological model: Soil and Water Assessment Tool (SWAT).
  • Calibration and sensitivity analysis: Sequential Uncertainty Fitting (SUFI-2) technique using SWAT-CUP.
  • Climate models: 13 General Circulation Models (GCMs) from Coupled Model Intercomparison Project-6 (CMIP6) for Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5).
  • Bias correction: Empirical Quantile Mapping (EQM).
  • Flood event identification: Annual Maximum Series (AMS) approach with empirical formulation for start/end dates, and the Recession Curve (RC) method (Wittenberg, 1999) for baseflow separation.
  • Seasonality analysis: Circular statistical method.
  • Sensitivity analysis: Quantile regression.
• Data sources:
  • Observed station data: Daily rainfall, maximum/minimum temperature, and streamflow from the National Hydro Power Corporation (NHPC), India, and the Department of Hydrology and Meteorology (DHM), Nepal.
  • Reanalysis data: ERA5 gridded rainfall and temperature data (0.1° spatial resolution).
  • Digital Elevation Model (DEM): ALOS PALSAR radiometric terrain corrected (RTC) product (30 m spatial resolution).
  • Land Use Land Cover (LULC) data: SWAT data for Europe/Asia (resampled, ~30 m resolution), derived from 1-kilometer Advanced Very High-Resolution Radiometer (AVHRR) data (Global Land Cover Characterization - GLCC).
  • Soil data: Terrain database for Nepal primary data (version 1.0, 1:1 million scale) from FAO and Survey Department Nepal.
  • Climate datasets: Bias-corrected CMIP6 GCM outputs for future precipitation and temperature.
  • Atmospheric drivers: El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Indian Ocean Dipole (IOD), and Atlantic Multidecadal Oscillation (AMO) for exploratory analysis.

Main Results

• Future floods are projected to have increased flood peaks and decreased flood durations compared to the historical period.
• The timing of future flood occurrences is delayed, on average, by 15 days, with potential variability of at least 40 days.
• While median flood volumes are comparable between historical and future periods, their distribution changes.
• Decadal analysis shows flood peaks increasing by 50% to 200% at Gopaghat and 10% to 50% at Banga. Flood volume at Gopaghat decreases until the 2070s then increases, while at Banga it steadily increases. Flood duration decreases at both stations, more significantly at Gopaghat.
• Flood properties (peak and volume) are more sensitive to changes in event precipitation than to concurrent air temperature, both historically and in future scenarios.
• A consistent monotonic increase in the sensitivity of flood peaks to both precipitation and temperature is observed for future warming scenarios across increasing quantiles of peak distribution.
• In future warming scenarios, a significant positive correlation exists between the sensitivity of flood peak and flood volume to both precipitation and temperature, indicating proportional changes in these flood characteristics.
• Exploratory analysis of large-scale atmospheric drivers revealed a statistically significant negative correlation between the previous year's average ENSO index and flood peak magnitude.

Contributions

• Provides a comprehensive assessment of climate change impacts on multiple flood properties (peak, volume, duration, seasonality, and sensitivity) in a critical mountainous catchment of the Nepal Himalayas, using the latest CMIP6 climate projections.
• Quantifies the differential sensitivity of flood peaks and volumes to precipitation versus temperature, highlighting the dominant role of precipitation in modulating flood dynamics in steep topography.
• Offers crucial insights for regional water and risk management, particularly for hydropower planning and flood defense strategies, by projecting changes in flood magnitude, timing, and duration.
• Demonstrates a transferable hydrological modeling framework, combining a calibrated SWAT model with globally available datasets, applicable to other mountainous catchments worldwide for comparative flood regime assessments.

Funding

• National Hydroelectric Power Corporation (NHPC), India, under the project “Study on Assessment of Impact of Climate Change on West Seti and SR-6 H.E. Projects” (Project Number: HYD-6003/23-24).
• DST INSPIRE Faculty Fellowship (DST/INSPIRE/04/2022/001952, Faculty Reference no. IFA22-EAS 114) from the Department of Science and Technology, Government of India (for Dr. Pankaj Dey).

Citation

@article{Kumar2025Impact,
  author = {Kumar, Sanjay and Dey, Pankaj and Yadav, Brijesh Kumar},
  title = {Impact of climate change on flood properties in a mountainous catchment of Nepal Himalayas},
  journal = {Natural Hazards},
  year = {2025},
  doi = {10.1007/s11069-025-07775-2},
  url = {https://doi.org/10.1007/s11069-025-07775-2}
}