Said et al. (2026) Water Demand and Surface Water Supply Dynamics in the Changing Climate of Semi-Arid Basins

Identification

• Journal: International Soil and Water Conservation Research
• Year: 2026
• Date: 2026-02-01
• Authors: Rania Bou Said, Rabi H. Mohtar, Roger Moussa
• DOI: 10.1016/j.iswcr.2026.100635

Research Groups

• Faculty of Agricultural and Food Sciences, American University of Beirut, Beirut, Lebanon
• Biological and Agricultural Engineering, Civil and Environmental Engineering, TAMU Energy Institute, Texas A&M University, College Station, TX, USA
• LISAH, Univ. Montpellier, INRAE, IRD, Institut Agro, Montpellier, France

Short Summary

This paper quantifies the short- and long-term impacts of climate change on potential evapotranspiration (PET) and surface water flow (Q) in the ungauged, semi-arid Kherbet Qanafar sub-basin (Lebanon), projecting significant declines in water supply (Q) by 38–52 % in the short term and up to 60 % in the long term, while PET changes are nominal.

Objective

• To gain a clear understanding of the possible climatic dynamics within the basin by examining the changes in long-term and short-term fluctuations in temperature and precipitation, and their quantitative impact on PET and Q across the basin under the SSP1 and SSP3 scenarios.
• To conduct a sensitivity analysis to identify key factors that influence the hydrological responses within the basin.
• To suggest immediate measures and long-term strategies to better manage water resources and ensure evidence-based decisions under climate change projections.

Study Configuration

• Spatial Scale: Kherbet Qanafar sub-basin, 9 square kilometers, located within the Litani Basin, Beqaa Valley, Lebanon.
• Temporal Scale:
  • Observed flow data: 2012–2019 (monthly average).
  • Observed weather data: 2012–2021 (daily).
  • Reference baseline for climate change data: 1995–2014.
  • Projection period: 2020–2100 (general), specifically 2022–2096.
  • Short-term analysis: 2022–2041 (5-year intervals).
  • Long-term analysis: 2022–2096 (5-year intervals).

Methodology and Data

• Models used:
  • Potential Evapotranspiration (PET): Hargreaves method.
  • Surface Water Flow (Q): Modèle du Génie Rural à 2 paramètres Mensuel (GR2M) lumped model.
• Data sources:
  • Weather data (maximum temperature, minimum temperature, precipitation, wind speed, relative humidity): Lebanese Agricultural Research Institute (LARI) Weather Station at Kherbet Qanafar Village.
  • Surface flow data (Q): Litani Water Authority (monthly average, 2012–2019).
  • Climate change data (maximum temperature, minimum temperature, precipitation for SSP1 and SSP3 scenarios): Coupled Model Intercomparison Project Phase 6 (CMIP6) via the World Bank's “Climate Change Knowledge Portal”.

Main Results

• The GR2M model was calibrated with a Nash-Sutcliffe Efficiency (NSE) of 0.723, indicating strong reliability in simulating streamflow for the Kherbet Qanafar sub-basin.
• Short-term (2022–2041):
  • Annual temperatures are projected to increase by 0.83 °C (SSP1) and 0.92 °C (SSP3) compared to the 1995–2014 baseline.
  • Average annual precipitation is predicted to be 640.7 mm (SSP1) and 607.9 mm (SSP3).
  • PET is expected to fluctuate between -1 % and 5 % (-2.9 mm to 7.86 mm) compared to 2022–2026, indicating no major short-term fluctuations.
  • Annual surface water flow (Q) is projected to decrease by 40 % by 2041 compared to 2022 under both SSP1 and SSP3 scenarios.
• Long-term (2022–2096):
  • Annual temperatures are predicted to increase by 0.76 °C (SSP1) and 3.38 °C (SSP3) compared to the 1995–2014 baseline.
  • Annual precipitation is expected to decrease by 23.65 mm (SSP1) and 77.84 mm (SSP3).
  • Mean surface water flow (Q) is expected to decrease significantly by 2091–2096 compared to 2022–2026: by 15 % (fall), 20 % (winter), 21 % (summer), and 24 % (spring) under SSP1, and drastically by 60 % across seasons under SSP3.
  • Extreme high-flow events, including potential flooding, are anticipated to occur every 15–20 years under both SSPs.
• Sensitivity Analysis: Streamflow is approximately three times more sensitive to the groundwater-exchange coefficient (x2) than to the soil-water storage capacity (x1). This suggests that variations in surface flow are primarily driven by climatic patterns and groundwater extraction rather than land-cover changes.

Contributions

• Provides quantitative hydrological projections for an ungauged, semi-arid sub-basin in Lebanon under CMIP6 SSP1 and SSP3 climate change scenarios, addressing data scarcity challenges in developing countries.
• Demonstrates the reliability of the GR2M model for simulating streamflow in data-limited regions, achieving an NSE of 0.723.
• Quantifies the projected short- and long-term impacts of climate change on PET and surface water flow, highlighting a critical decline in water supply despite nominal changes in water demand.
• Identifies the groundwater-exchange coefficient as a significantly more influential parameter on surface water flow than soil moisture capacity, emphasizing the importance of groundwater management.
• Offers actionable immediate and long-term strategies for sustainable water resource management, including fair water allocation, efficient irrigation techniques, adoption of non-conventional water sources, managed aquifer recharge, and a shift to low-water-requirement crops.

Funding

• Middle East Partnership Initiative (MEPI) scholarship (for Rania Bou Said).
• French National Research Institute for Agriculture, Food and the Environment (INRAE) for hydrological modelling trainings.
• Laboratoire d’Etude des Interactions Sol-AgroSystème-Hydrosystème (LISAH).

Citation

@article{Said2026Water,
  author = {Said, Rania Bou and Mohtar, Rabi H. and Moussa, Roger},
  title = {Water Demand and Surface Water Supply Dynamics in the Changing Climate of Semi-Arid Basins},
  journal = {International Soil and Water Conservation Research},
  year = {2026},
  doi = {10.1016/j.iswcr.2026.100635},
  url = {https://doi.org/10.1016/j.iswcr.2026.100635}
}