Hidayatulloh et al. (2026) From dry Wadi bed to flashflood: decoding climate-driven flood hazards in arid environments, Saudi Arabia

Identification

• Journal: Natural Hazards
• Year: 2026
• Date: 2026-02-01
• Authors: Asep Hidayatulloh, Jarbou Bahrawi, Mohamed Elhag
• DOI: 10.1007/s11069-025-07787-y

Research Groups

• Department of Water Resources, Faculty of Environmental Sciences, King Abdulaziz University, Jeddah, Saudi Arabia
• The State Key Laboratory, of Remote Sensing, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing, China
• Laboratory of Ecohydraulics & Inland Water Management, Department of Ichthyology and Aquatic Environment, University of Thessaly, Nea Ionia, Magnisias, Greece
• Department of Geoinformation in Environmental Management, CI-HEAM/Mediterranean Agronomic Institute of Chania, Chania, Greece
• Department of Applied Geosciences, Faculty of Science, German University of Technology in Oman, Muscat, Oman

Short Summary

This study quantifies future climate-driven flash flood hazards in the Wadi Ibrahim catchment, Makkah, by coupling downscaled climate projections with 2D hydrodynamic modeling, revealing a significant intensification of flood volumes, depths, and hazard zones under RCP 4.5 and RCP 8.5 scenarios.

Objective

• Project future extreme rainfall depths using bias-corrected climate model data and frequency analysis.
• Simulate flood inundation extent, depth, volume, and peak discharge under current and future climate scenarios.
• Analyze the evolution of flood hazard zones.
• Validate simulated peak discharges and volumes against established regional envelope curves.
• Provide scientifically robust insights to inform urgent upgrades to flood protection infrastructure and early warning systems for safeguarding lives, the Grand Mosque precinct, and critical urban infrastructure against escalating climate-driven flood risks.

Study Configuration

• Spatial Scale: Wadi Ibrahim Watershed, Makkah Al-Mukarramah City, Saudi Arabia, spanning approximately 120 km². High-resolution 2D grid modeling.
• Temporal Scale: Historical rainfall data from 1967–2022 (J114) and 2017–2024 (other stations); climate projections (SSP2-4.5 and SSP5-8.5, equivalent to RCP 4.5 and RCP 8.5) spanning 2006–2100 with a focus on mid-century (2040–2070); flood simulations over a 48-hour horizon for 50-, 100-, and 200-year return periods.

Methodology and Data

• Models used:
  • HEC-RAS (two-dimensional Rain-on-Grid hydrodynamic model)
  • HEC-HMS (hydrological model for rainfall-runoff dynamics using SCS-CN methods)
  • CORDEX (Coordinated Regional Climate Downscaling Experiment) MENA domain, specifically SMHI-RCA4 Regional Climate Model (RCM) driven by NOAA-GFDL-ESM2M Global Climate Model (GCM) for climate projections.
  • CMhyd tool for bias correction of climate data.
  • Gumbel distribution for rainfall frequency analysis.
• Data sources:
  • Copernicus Digital Elevation Model (DEM) 2021 release (30-meter resolution).
  • Rainfall data from six local stations (J114, MK139, Al Adel, Mena, Electricity, Al Maesem).
  • Land Cover (2023 Sentinel-2 classification).
  • Regional soil texture maps and Antecedent Moisture Conditions (AMC-II) for Curve Number (CN) derivation.
  • Regional envelope curves for flood validation.

Main Results

• Present-day flood volumes range from 18.9 × 10^6 m^3 (50-year event) to 24.8 × 10^6 m^3 (200-year event), with an average inundation depth of 0.2 m for the 200-year event.
• Under RCP 4.5, flood volumes nearly double, reaching 33.4 × 10^6 m^3 (50-year) and 64.9 × 10^6 m^3 (200-year), with average depths increasing to 0.6 m.
• Under RCP 8.5, flood volumes triple, peaking at 44.5 × 10^6 m^3 (50-year) and 86.1 × 10^6 m^3 (200-year), and average depths rising to 0.8 m.
• High-hazard zones (> 2 m depth) expand from 7.2–9.8 km^2 under current conditions to 5.3–12.0 km^2 under RCP 4.5, and significantly to 9.5–16.6 km^2 under RCP 8.5.
• Peak discharges for 100- and 200-year events under RCP 4.5 and RCP 8.5 exceed the established Saudi Arabian envelope curve, indicating non-stationary extreme flood events.
• Climate forcing (emission intensity) is identified as the principal flood hazard multiplier, exerting a stronger control on flood severity than return period progression alone.

Contributions

• Provides the first comprehensive, high-resolution 2D hydrodynamic assessment of future climate-driven flash flood hazards in the critical Wadi Ibrahim catchment, Makkah, integrating CORDEX-downscaled rainfall under RCP 4.5 and RCP 8.5 scenarios.
• Quantifies the projected intensification of flood volumes, depths, and spatial extent of hazard zones, demonstrating that future extreme events will significantly surpass historical design standards.
• Highlights the non-stationarity of flood extremes, showing that future peak discharges for higher return periods exceed existing regional envelope curves, necessitating their urgent update.
• Offers scientifically robust insights crucial for informing adaptive flood management strategies, including infrastructure upgrades (e.g., enlarged culverts, detention basins) and the development of real-time early-warning systems to protect lives and critical infrastructure, including the Grand Mosque environs.

Funding

This project was funded by the Deanship of Scientific Research (DSR) at King Abdulaziz University, Jeddah, under grant no. IPP: 118-155-2025.

Citation

@article{Hidayatulloh2026From,
  author = {Hidayatulloh, Asep and Bahrawi, Jarbou and Elhag, Mohamed},
  title = {From dry Wadi bed to flashflood: decoding climate-driven flood hazards in arid environments, Saudi Arabia},
  journal = {Natural Hazards},
  year = {2026},
  doi = {10.1007/s11069-025-07787-y},
  url = {https://doi.org/10.1007/s11069-025-07787-y}
}