Arnáez et al. (2026) Hydrological Challenges and Competing Demands in the Mediterranean Region

Identification

• Journal: Water Resources Management
• Year: 2026
• Date: 2026-02-01
• Authors: José Arnáez, Estela Nadal-Romero, Noemí Solange Lana-Renault, José M. García‐Ruiz
• DOI: 10.1007/s11269-025-04467-1

Research Groups

• Area of Physical Geography, University of La Rioja, Spain
• Instituto Pirenaico de Ecología (IPE-CSIC), Zaragoza, Spain

Short Summary

This review examines the severe hydrological challenges in the Mediterranean region, highlighting the growing conflicts between declining water resources in mountainous headwaters (due to climate change and revegetation) and increasing water demand in lowlands (driven by agriculture, tourism, and urban expansion), which leads to environmental and social tensions.

Objective

• To present the primary challenges concerning surface water availability in the Mediterranean region, particularly in European countries.
• To examine the complex interactions between factors explaining river regimes, streamflow evolution, and their consequences for sediment yield and river dynamics.
• To assess conflicts between runoff generation in the highlands and water consumption in the lowlands in an integrated manner.

Study Configuration

• Spatial Scale: The entire Mediterranean region, with specific focus on European countries (e.g., Spain, Italy, France, Greece, Portugal), North Africa (e.g., Morocco, Tunisia, Egypt), and the Middle East (e.g., Lebanon, Israel). This includes mountain ranges (Alps, Pyrenees, Atlas), major river basins (Po, Ebro, Rhône, Nile), and coastal lowlands.
• Temporal Scale: Multi-decadal to over a century, covering trends since the mid-20th century (e.g., 1871–2020 for precipitation, 1979–2024 for temperature anomalies, 1958–2017 for snow cover, 1991–2025 for literature review period).

Methodology and Data

• Models used: The review synthesizes findings from studies that used hydrological models such as RHESSys and HSPF.
• Data sources: A comprehensive literature review of 176 publications (1991–2025) from Scopus and Web of Science, supplemented by extensive data produced by the authors themselves. This includes observational data, reanalysis data, and climate projections (e.g., IPCC reports).

Main Results

• Mountainous areas are critical for runoff generation, but climate change (rising temperatures, increased evaporative demand, more frequent droughts) and land use changes (woody encroachment, reforestation) have reduced water yield and altered river regimes.
• River discharge has significantly declined, with estimates showing a reduction of approximately 30% in water yield over 50 years in some areas and a 40% reduction in the Ebro River mouth discharge. Projections indicate a 19% mean runoff decline across 262 Mediterranean basins by the end of the 21st century, potentially reaching 39% in extreme scenarios.
• Rising temperatures have led to earlier snowmelt, advancing spring runoff peaks (e.g., Po River peak shifted from May to April), and significant glacier shrinkage (e.g., Italian Alps glacier area declined by 23% between 1973–2017, Pyrenean glaciers lost 6.3 meters thickness from 2011–2020).
• Lowland areas face unsustainable water demand, primarily from irrigated agriculture (accounting for 85% of withdrawals in Spain, 50% in Italy), tourism, and urban/industrial centers. Irrigated land in Spain grew from 1.3 million hectares in 1940 to 3.7 million hectares in 2004.
• This imbalance has led to severe hydrological conflicts, including large-scale river water extractions, groundwater depletion (e.g., Doñana National Park water table lowered by more than 6 meters), coastal salinization (e.g., Nile, Ebro, Po deltas), and wetland degradation.
• Dam construction, while securing water supply, has drastically reduced sediment delivery to deltas (e.g., Ebro Delta receives only 3% of its historical sediment load, Nile flow reduced from 2700 cubic meters per second to approximately 150 cubic meters per second), contributing to their retreat.

Contributions

• Provides a comprehensive synthesis of the complex, interacting factors driving hydrological challenges and conflicts in the Mediterranean region, integrating climate change, land use change, and socio-economic demands.
• Highlights the critical dichotomy between water generation in highlands and consumption in lowlands as a central issue for water management.
• Identifies specific environmental consequences of these conflicts, including river discharge reduction, groundwater depletion, coastal salinization, and wetland degradation.
• Proposes a framework for future management strategies, emphasizing the need for improved understanding, optimized mountain water yield, and demand reduction in lowlands through adaptive governance and socio-hydrological scenarios.

Funding

• MOUNTWATER research project (TED2021-131982BeI00 and MCIN/AEI/https://doi.org/10.13039/501100011033), funded by the MICINN and NextGeneration EU/PRTR.
• FORWARD project (PID2024-1613140B-100), funded by the MICINN-FEDER.
• Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.

Citation

@article{Arnáez2026Hydrological,
  author = {Arnáez, José and Nadal-Romero, Estela and Lana-Renault, Noemí Solange and García‐Ruiz, José M.},
  title = {Hydrological Challenges and Competing Demands in the Mediterranean Region},
  journal = {Water Resources Management},
  year = {2026},
  doi = {10.1007/s11269-025-04467-1},
  url = {https://doi.org/10.1007/s11269-025-04467-1}
}