Khan et al. (2026) A scalable framework for flash flood hazard assessment in data-scarce catchments using coupled modeling

Identification

• Journal: Modeling Earth Systems and Environment
• Year: 2026
• Date: 2026-03-03
• Authors: Moiz Ahmed Khan, Muhammad Masood, Mudassar Iqbal, Saliha Qamar, Muhammad Awais Zafar, Khalil Ahmad
• DOI: 10.1007/s40808-026-02751-6

Research Groups

• Centre of Excellence in Water Resources Engineering, UET, Lahore, Pakistan
• Herff College of Engineering, The University of Memphis, Memphis, TN, USA

Short Summary

This study developed a scalable framework for flash flood hazard assessment in data-scarce catchments by coupling HEC-HMS and HEC-RAS 2D with remotely sensed data and transposed rainfall. The framework successfully mapped flood hazards for various return periods, revealing a significant increase in extreme hazard zones from 514 hectares (2%) to 2,498 hectares (7%) between 10-year and 100-year return period floods.

Objective

• To develop a robust and transferable framework for flash flood hazard assessment in data-scarce and ungauged catchments using coupled hydrological (HEC-HMS) and 2D hydraulic (HEC-RAS) modeling, driven by transposed rainfall data.

Study Configuration

• Spatial Scale: Vidor Hill Torrent catchment, southwestern Punjab, Pakistan (approximately 1,346 square kilometers).
• Temporal Scale: Rainfall data from 1971–2022 (Barkhan station, transposed for 1983–2022 for Vidor); model calibrated using the 2022 flood event; simulations for 10, 25, 50, and 100-year return periods.

Methodology and Data

• Models used:
  • Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) version 4.11
  • Hydrologic Engineering Center’s River Analysis System (HEC-RAS) 2D unsteady flow model version 6.4.1
• Data sources:
  • Rainfall: Conventional Weather Stations (Pakistan Meteorological Department), transposed from Barkhan station.
  • Soil parameters: Harmonized World Soil Database (HWSD).
  • Digital Elevation Models (DEMs): SRTM DEM (30 meters resolution) for HEC-HMS, ALOS PALSAR DEM (12.5 meters resolution) for HEC-RAS.
  • Land Use/Land Cover (LULC): Sentinel-2 imagery (10 meters resolution), classified.
  • Flood extent validation: Sentinel-1 SAR imagery (VH polarization band), processed in Google Earth Engine (GEE).
  • Calibration data: 100-year return period flood hydrograph (Punjab Irrigation Department, based on 2022 event).

Main Results

• HEC-HMS model calibration for the 100-year flood event achieved a Nash–Sutcliffe Efficiency (NSE) of 0.948, Root Mean Square Error (RMSE) of 0.2, and Percent Bias (PBIAS) of −16.88%. The simulated peak flow (5026.2 cubic meters per second) deviated by only 1.8% from the observed (4937.42 cubic meters per second).
• Simulated peak flows increased with return period: 2544.74 cubic meters per second (10-year), 3450.93 cubic meters per second (25-year), 4268.04 cubic meters per second (50-year), and 5026.2 cubic meters per second (100-year).
• Total inundated area increased from 33,146.36 hectares (24.62% of catchment) for the 10-year event to 34,160.97 hectares (25.38%) for the 100-year event.
• Flood velocities intensified, with large sections of the floodplain exhibiting velocities between 2.0 and 3.0 meters per second, and isolated hotspots surpassing 3.0 meters per second for the 100-year event.
• HEC-RAS 2D model validation against Sentinel-1 SAR imagery for the 100-year flood showed a Probability of Detection (POD) of 0.952, a False Alarm Ratio (FAR) of 0.456, and a Critical Success Index (CSI) of 0.529. The Bias Score of 1.75 indicated a tendency to over-predict flood extent.
• Flood hazard mapping revealed a progressive increase in extreme hazard zones from 514 hectares (2%) for the 10-year return period to 2,498 hectares (7%) for the 100-year return period. Low hazard areas decreased from 27,500 hectares (83%) to 26,683 hectares (78%).

Contributions

• Successfully integrated rainfall transposition with event-based HEC-HMS and HEC-RAS 2D simulations to achieve high-quality flood hazard outputs in ungauged, data-scarce catchments.
• Developed a practical and transferable methodology for flash flood hazard assessment that simplifies data requirements while preserving the physical consistency of rainfall inputs.
• Provided actionable flood hazard maps for different return periods, supporting flood risk management, land-use planning, and disaster preparedness in vulnerable regions.

Funding

• Not applicable (No funding was available).

Citation

@article{Khan2026scalable,
  author = {Khan, Moiz Ahmed and Masood, Muhammad and Iqbal, Mudassar and Qamar, Saliha and Zafar, Muhammad Awais and Ahmad, Khalil},
  title = {A scalable framework for flash flood hazard assessment in data-scarce catchments using coupled modeling},
  journal = {Modeling Earth Systems and Environment},
  year = {2026},
  doi = {10.1007/s40808-026-02751-6},
  url = {https://doi.org/10.1007/s40808-026-02751-6}
}