Al-Hilali et al. (2025) Effects of climate change on precipitation and runoff in semi-arid regions: future scenarios and implications for water

Identification

• Journal: Theoretical and Applied Climatology
• Year: 2025
• Date: 2025-12-01
• Authors: Sahar Sameer Al-Hilali, Ahmed Ali Hassan, A. Moussa, Sherien Ahmed Zahran, Samia Abou El-Fotouh
• DOI: 10.1007/s00704-025-05949-3

Research Groups

• Dams and Water Resources Engineering Department, College of Engineering, University of Mosul, Mosul, Iraq
• Irrigation and Hydraulics Department, Faculty of Engineering, Ain Shams University, Cairo, Egypt
• Coastal Research Institute, National Water Research Center, Alexandria, Egypt
• Environment and Climate Change Research Institute, National Water Research Center, Cairo, Egypt

Short Summary

This study investigates the impact of climate change on precipitation and runoff in Northwestern Iraq under a high emission scenario (RCP8.5), using regional climate and hydrological models. It projects a significant decrease in annual precipitation and a substantial reduction in annual runoff in the Al-Khoser River Basin by the end of the century, highlighting the need for water harvesting solutions.

Objective

• To examine variations in yearly, seasonal, and monthly precipitation stemming from climate change under a high emission scenario (RCP8.5) for four major stations in Northwestern Iraq.
• To assess the implications of these precipitation changes for runoff flow in the Al-Khoser River Basin.

Study Configuration

• Spatial Scale: Northwestern Iraq, focusing on four stations (Dohuk, Mosul, Tal-Afar, Rabia) and the Al-Khoser River Basin (area of 694 km²).
• Temporal Scale:
  • Baseline: 1970–2005
  • Future Projections: 2006–2039 (near future), 2040–2069 (mid-century), 2070–2099 (end of century).

Methodology and Data

• Models used:
  • Regional Climate Model: RegCM4-7 (driven by Global Climate Model MIROC-MIROC5)
  • Hydrological Model: HEC-HMS (version 4.11)
  • Bias Correction: Distribution Mapping (using Gamma distribution)
  • Infiltration Loss: Deficit and Constant method (linked to simple canopy and simple surface methods)
  • Runoff Transmission: Soil Conservation Services-Unit Hydrograph (SCS-UH)
• Data sources:
  • Observed precipitation data: Iraqi Meteorological Organization and Seismology (IMOS) for four stations (Dohuk, Mosul, Tal-Afar, Rabia), with daily data for Mosul and Dam stations.
  • Simulated climate data: CORDEX platform (http://cordexesg.dmi.dk/esgf-web-fe/) for MIROC-RegCM4-7 model (0.22° / 25 km resolution) under RCP8.5 emission scenario.
  • Al-Khoser Basin characteristics (land cover, soil texture, saturated hydraulic conductivity): Previous field measurements by Mohammad (2005).
  • Observed storm data for HEC-HMS calibration/verification: Mohammad (2005) for five storms at Al-Khoser Basin outlet (2002-2004).

Main Results

• Precipitation Projections:
  • Annual precipitation: Overall decrease during the 2006–2099 period across all stations.
  • Near future (2006–2039): Slight increase in average annual precipitation (e.g., Duhok 11%, Mosul 7%, Rabia 2.5%).
  • Mid-century (2040–2069): Decrease in annual precipitation (not exceeding 2% at all stations).
  • End of century (2070–2099): Significant decrease in annual precipitation (ranging from 5% to 12% across stations, e.g., Duhok 12%, Mosul 5%).
  • Interannual variability: Increased variability in annual precipitation, particularly during 2006–2039 and 2070–2099, with more years experiencing below-average precipitation by the end of the century.
  • Seasonal precipitation: General decrease in winter (up to 19.3% by 2070–2099), general increase in spring, and general decrease in autumn.
  • Monthly precipitation: Irregular increases and decreases, leading to increased monthly distribution variation, with January showing the highest decrease by 2070–2099.
• Bias Correction Performance: Distribution Mapping effectively removed bias from daily precipitation data, with the Bias Percent (BP) approaching zero.
• HEC-HMS Model Performance: Achieved good performance during calibration and verification with Bias Percent (BP) of 4.8% for flow and 12.9% for runoff volume, and Nash Sutcliffe Coefficient (NS) values of 0.95 for flow and 0.99 for runoff volume.
• Runoff Projections:
  • Annual runoff volume in the Al-Khoser Basin is projected to decrease.
  • Decrease rates compared to the baseline (1970–2005): 15% during 2006–2039, 22% during 2040–2069, and 33% during 2070–2099.
  • The decrease in runoff, even with an initial increase in average annual precipitation, is attributed to a decrease in the number of precipitation events equal to or greater than 10 mm, which are critical for generating surface runoff.
• Runoff-Precipitation Relationship: A new empirical equation was developed to estimate annual runoff depth based on the total depth of precipitation exceeding 10 mm, achieving a high coefficient of determination (0.96).

Contributions

• First study to evaluate future precipitation changes (annual, seasonal, monthly) in Northwestern Iraq using the MIROC-RegCM4-7 Regional Climate Model under the RCP8.5 emission scenario.
• Comprehensive assessment of climate change impacts on runoff in the Al-Khoser River Basin, a semi-arid region with limited previous research, using the HEC-HMS model.
• Demonstrated the critical role of precipitation events exceeding a specific threshold (10 mm) in generating runoff in semi-arid regions, leading to a more accurate empirical runoff-precipitation relationship.
• Provided quantitative support for decision-making regarding water resource management, specifically advocating for the establishment of rainwater harvesting dams in the Al-Khoser River Basin to mitigate water scarcity under future climate scenarios.

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Citation

@article{AlHilali2025Effects,
  author = {Al-Hilali, Sahar Sameer and Hassan, Ahmed Ali and Moussa, A. and Zahran, Sherien Ahmed and El-Fotouh, Samia Abou},
  title = {Effects of climate change on precipitation and runoff in semi-arid regions: future scenarios and implications for water},
  journal = {Theoretical and Applied Climatology},
  year = {2025},
  doi = {10.1007/s00704-025-05949-3},
  url = {https://doi.org/10.1007/s00704-025-05949-3}
}