Aminzadeh et al. (2025) Water storage paradox of reservoir expansion and evaporative losses in the MENA region

Identification

• Journal: Scientific Reports
• Year: 2025
• Date: 2025-10-01
• Authors: Milad Aminzadeh, Sankeerth Narayanaswamy, Hannes Nevermann, Matteo Zampieri, Ibrahim Hoteit, Paolo D’Odorico, Amir AghaKouchak, Kaveh Madani, Nima Shokri
• DOI: 10.1038/s41598-025-21859-w

Research Groups

• Institute of Geo-Hydroinformatics, Hamburg University of Technology, Hamburg, Germany
• United Nations University Hub on Engineering to Face Climate Change at the Hamburg University of Technology, United Nations University Institute for Water, Environment and Health (UNU-INWEH), Hamburg, Germany
• Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
• Climate Change Center (CCC), National Center for Meteorology (NCM), Jeddah, Saudi Arabia
• Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA
• Department of Civil and Environmental Engineering, University of California, Irvine, CA, USA
• United Nations University Institute for Water, Environment and Health (UNU-INWEH), Richmond Hill, ON, Canada

Short Summary

This study quantifies the storage capacity and evaporative losses of over 133,700 small agricultural reservoirs (< 0.1 km²) in the Middle East and North Africa (MENA) region from 2016 to 2023, revealing a paradox where high evaporation rates, potentially exceeding 2.4 x 10⁹ cubic meters annually, significantly undermine their storage efficiency despite their crucial role in water supply.

Objective

• To provide a systematic assessment of small agricultural reservoirs (< 0.1 km²) across the MENA region from 2016 to 2023, quantifying both their annual storage capacity and evaporative losses by integrating fine-resolution satellite imagery with physics-based modeling.

Study Configuration

• Spatial Scale: Middle East and North Africa (MENA) region, covering -18.42° to 78.60°E and -1.80° to 44.47°N, analyzed within 50 km × 50 km grid cells. Focus on small agricultural reservoirs with surface areas less than 0.1 km².
• Temporal Scale: Annual assessment from 2016 to 2023.

Methodology and Data

• Models used:
  • Physically-based evaporation model (Aminzadeh et al., 2018, 2024) for quantifying evaporative fluxes.
  • Power-law relationship (Mady et al., 2020) for estimating reservoir storage capacity based on size distribution.
  • Normalized Difference Water Index (NDWI) with a threshold of 0.2 for water body detection.
• Data sources:
  • Sentinel-2 satellite images (10 m resolution) for identifying and mapping small water reservoirs.
  • Google Earth Engine for accessing and processing satellite imagery.
  • Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis datasets (0.625° × 0.5° resolution) for meteorological variables (wind speed, air temperature, humidity, radiation).
  • ESA WorldCover v200 land cover map (10 m resolution) and ESRI’s global 10-m land-cover data (2017-2023) for agricultural land extent and cropland area.
  • MERIT Hydro dataset for masking water canals and ephemeral streams.
  • ERA5-Land Daily Aggregated dataset (0.1° resolution) for annual precipitation and potential evapotranspiration.
  • Global irrigation water use estimates (Zhang et al., 2022) and GLW 4 Gridded Livestock Density dataset (10 km resolution) combined with species-specific water consumption for agricultural water use.
  • Direct evaporation measurements from Cartagena, Spain (April 2007–March 2008) and Isfahan, Iran (April 2019–March 2020) for model validation (RMSE of 14.38 mm).

Main Results

• Over 133,700 small agricultural reservoirs were identified in the MENA region, peaking in 2020, with a combined surface area of 1,408 km².
• The largest cumulative reservoir areas are located in Türkiye (309 km²), Pakistan (234 km²), Iran (168 km²), Iraq (108 km²), and Egypt (64 km²).
• The total storage capacity of these reservoirs reached 1.243 x 10⁹ cubic meters in 2020.
• Annual evaporative losses from these reservoirs may potentially exceed 2.4 x 10⁹ cubic meters, with a mean annual loss of 1.74 x 10⁹ cubic meters.
• Hotspots of cumulative evaporation, where rates can exceed 3,000 mm/year (3 m/year), correspond to regions with high reservoir surface area, including southern Pakistan, southwestern Iran, and southeastern Iraq.
• The volume of water potentially lost through evaporation annually can be as much as double the storage capacity of the reservoirs.
• Evaporation rates from reservoirs increase with rising air temperature, wind speed, and solar radiation, and decrease with higher humidity.
• The expansion of reservoirs shows positive correlations with the aridity index and cropland area, indicating strong climatic and anthropogenic influences.
• Small agricultural reservoirs contribute up to 16% of irrigation and livestock water use in most MENA countries.

Contributions

• Provides the first regional, annual, fine-resolution inventory of small agricultural reservoirs (< 0.1 km²) and their associated evaporative losses across the MENA region.
• Quantifies the significant, often overlooked, evaporative water losses from small reservoirs, highlighting a critical "water storage paradox" in water-stressed regions.
• Identifies geographical hotspots of reservoir expansion and evaporative losses, linking them to climatic and agricultural drivers.
• Offers crucial data and insights for developing targeted water management strategies, evaporation suppression techniques, and improved reservoir design to enhance agricultural water security.
• Establishes a benchmark for future assessments of similar challenges in other semi-arid regions globally.

Funding

• Projekt DEAL

Citation

@article{Aminzadeh2025Water,
  author = {Aminzadeh, Milad and Narayanaswamy, Sankeerth and Nevermann, Hannes and Zampieri, Matteo and Hoteit, Ibrahim and D’Odorico, Paolo and AghaKouchak, Amir and Madani, Kaveh and Shokri, Nima},
  title = {Water storage paradox of reservoir expansion and evaporative losses in the MENA region},
  journal = {Scientific Reports},
  year = {2025},
  doi = {10.1038/s41598-025-21859-w},
  url = {https://doi.org/10.1038/s41598-025-21859-w}
}