Villani et al. (2025) Large dams and small reservoirs: co-modeling water storage strategies in a Mediterranean catchment under a changing climate

Identification

• Journal: Frontiers in Water
• Year: 2025
• Date: 2025-10-28
• Authors: Lorenzo Villani, Giulio Castelli, Eleonora Forzini, Luigi Piemontese, Enrico Lucca, Ismail Bouizrou, Marco Lompi, Gabriele Bertoli, Ada Giuliano, Davide Danilo Chiarelli, Xenia Schneider, Tommaso Pacetti, Enrica Caporali, Elena Bresci
• DOI: 10.3389/frwa.2025.1673203

Research Groups

• Department of Agriculture, Food, Environment and Forestry (DAGRI), University of Florence, Florence, Italy
• Institute of Ecology and Landscape, Hochschule Weihenstephan-Triesdorf University (HSWT), Freising, Germany
• Department of Civil and Environmental Engineering, University of Florence, Florence, Italy
• Department of Civil and Environmental Engineering, Politecnico di Milano, Milan, Italy
• XPRO Consulting Limited, Strovolos, Cyprus

Short Summary

This study co-models water storage strategies (small agricultural reservoirs and a large dam) in a Mediterranean catchment under climate change, finding that future annual average water stored in both reservoir types is projected to decline by 6.3% by the end of the century due to reduced inflows and enhanced evaporation.

Objective

• Co-develop a hydrological model with local actors to simulate the effect of numerous small agricultural reservoirs (SmARs).
• Compare the effects on hydrological indicators of two types of water storage strategies (SmARs and a large dam) in the current climate.
• Simulate future climate and hydrological characteristics, focusing on reservoirs’ water stored, seepage, and evaporation in the Orcia catchment, comparing SmARs of different sizes and the large dam.

Study Configuration

• Spatial Scale: Orcia River catchment, Central Italy, covering 748 square kilometers.
• Temporal Scale: Baseline simulations from 2010 to 2020; climate change simulations for historical (1981–2014), near future (2009–2040), middle future (2035–2070), and far future (2065–2100) periods, with comparisons at 2.0 °C warming level and end of the century (2071–2100).

Methodology and Data

• Models used:
  • SWAT+ (v60.5.4) for hydrological modeling.
  • QSWAT+ v2.4.0 for watershed delineation and HRU creation.
  • SWAT+Editor v2.3.3 for data integration and parameter modification.
  • SWAT+Toolbox for calibration and validation.
  • HEC-RAS for deriving the gauging station rating curve.
• Data sources:
  • Daily maximum/minimum temperatures, precipitation, wind speed, relative humidity, solar radiation from CMIP6 bias-corrected General Circulation Models (GCMs) via ISIMIP3b climate input data (GFDL-ESM4, IPSL-CM6A-LR, MPI-ESM1-2-HR, MRI-ESM2-0, UKESM1-0-LL).
  • Historical precipitation and temperature data from Tuscany Region Hydrological Service (SIR).
  • Monthly actual evapotranspiration from MODIS16A2 remote sensing product.
  • Digital Elevation Model (DEM) (10 meter resolution) and river network from Tuscany Region.
  • Corine land use map and soil map from Tuscany Region.
  • Agricultural census data (ISTAT 2010, 2020) and ARTEA (2022) for cropland and irrigated area.
  • Shapefile of 1,097 SmARs from LaMMA consortium.
  • Information on the planned San Piero in Campo dam from Consorzio di Bonifica 6 Toscana Sud.
  • CO2 concentration values from ISIMIP3b atmospheric composition inputs.

Main Results

• By the end of the century under SSP585, the ensemble mean projects an average temperature rise of 4.9 ± 1.3 °C and a precipitation decrease of 156 ± 29 mm (-18.8%).
• Annual average water yield, percolation, and actual evapotranspiration are projected to decrease by 33%, 22%, and 11% respectively, while irrigation and potential evapotranspiration increase by 45.5% and 15%.
• Future annual average water stored in all reservoirs is expected to decline by 1.48 ± 0.42 million cubic meters (-6.3%) by the end of the century, driven by reduced inflows (-30%) and enhanced evaporation (8.7%).
• Seepage from all reservoirs is projected to decrease by 0.37 ± 0.11 million cubic meters (-9.8%) by 2100.
• Smaller reservoirs (SmARs) are more susceptible to climate change, experiencing water storage reductions of up to -21%, primarily due to reduced inflows.
• The large dam shows a smaller water storage reduction (-3.1%) but a significant increase in evaporation (17.9%).
• Both SmARs and the large dam reduce peak flows by up to 8.6% when simulated simultaneously, with average river flows reduced by no more than 3.4%.
• The co-modeling approach, involving local actors throughout the process, improved the quality and applicability of the research outputs.

Contributions

• Provides a direct comparison of the hydrological impacts of small agricultural reservoirs (SmARs) and a planned large dam under current and future climate conditions, a comparison often lacking in existing literature.
• Utilizes a highly detailed, process-based hydrological model (SWAT+) to simulate complex water dynamics, including numerous small reservoirs, at an unprecedented level of detail for the study area.
• Integrates a comprehensive co-modeling approach guided by the RRI Roadmap©TM, ensuring active stakeholder involvement from problem articulation to model application, thereby enhancing the relevance, acceptance, and legitimacy of the research findings for local water management.
• Quantifies the differential susceptibility of various reservoir sizes to climate change impacts, highlighting that smaller reservoirs are more vulnerable to reduced inflows while larger ones face greater increases in evaporation.
• Offers valuable insights for developing context-specific, integrated watershed management practices and adaptation strategies in Mediterranean catchments facing water scarcity under a changing climate.

Funding

• AG-WaMED Project (CUP B53C22004860003), funded by the Partnership for Research and Innovation in the Mediterranean Area Programme (PRIMA), an Art.185 initiative supported and funded under Horizon 2020, the European Union’s Framework Programme for Research and Innovation, Grant Agreement Number [Italy: 391 del 20/10/2022, Egypt: 45878, Tunisia: 0005874-004-18-2022-3, Greece: Γ Γ P21-0474657, Spain: PCI2022-132929, Algeria: N◦04/PRIMA_section 2/2021].
• RETURN Extended Partnership, funded by the European Union Next-GenerationEU (National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.3 – D.D. 1243 2/8/2022, PE0000005).

Citation

@article{Villani2025Large,
  author = {Villani, Lorenzo and Castelli, Giulio and Forzini, Eleonora and Piemontese, Luigi and Lucca, Enrico and Bouizrou, Ismail and Lompi, Marco and Bertoli, Gabriele and Giuliano, Ada and Chiarelli, Davide Danilo and Schneider, Xenia and Pacetti, Tommaso and Caporali, Enrica and Bresci, Elena},
  title = {Large dams and small reservoirs: co-modeling water storage strategies in a Mediterranean catchment under a changing climate},
  journal = {Frontiers in Water},
  year = {2025},
  doi = {10.3389/frwa.2025.1673203},
  url = {https://doi.org/10.3389/frwa.2025.1673203}
}