Kok et al. (2026) Ecosystem service trade-offs of upstream afforestation: an integrated hydrological-economic assessment in the Sorraia basin, Portugal

Identification

• Journal: Frontiers in Environmental Science
• Year: 2026
• Date: 2026-09-22
• Authors: S. Kok, L. Hein, S. Le Clec'h, J.P. Nunes, M. Glavan
• DOI: 10.3389/fenvs.2026.1838037

Research Groups

• Earth Systems and Global Change, Wageningen University and Research, Wageningen, Netherlands
• Urban Resilience and Spatial Transformation, Deltares, Delft, Netherlands
• Soil Physics and Land Management, Wageningen University and Research, Wageningen, Netherlands
• Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia

Short Summary

This study conducted an integrated hydrological-economic assessment of upstream afforestation scenarios in the Sorraia basin, Portugal, revealing that restoring native cork-oak forests (RESTOAK) generates substantial net welfare gains, while expanding eucalyptus plantations (EUCINT) results in net welfare losses, despite both improving water quality.

Objective

• To assess the basin-wide economic implications of upstream afforestation scenarios (eucalyptus expansion vs. native cork-oak restoration) by linking economic valuation to a process-based hydrological model, evaluating impacts on reservoir inflows, water quality, sediment dynamics, and related ecosystem services under current and future climate conditions.

Study Configuration

• Spatial Scale: Sorraia basin, Portugal (7,730 km²), focusing on upstream areas of the Montargil and Maranhão reservoirs.
• Temporal Scale:
  • Climate conditions: Historical (1976–2005) and mid-century future (2041–2070).
  • Economic assessment appraisal period: 2025–2070.
  • Sediment management costs planning horizon: 100 years.

Methodology and Data

• Models used:
  • Hydrological: SWAT2012 (Soil and Water Assessment Tool).
  • Economic: Integrated hydrological-economic assessment framework using various valuation approaches (market prices for land-use returns, avoided damage costs for sediment management, demand function for recreation, replacement costs for water purification).
• Data sources:
  • Land cover: Portuguese land use maps (COS 2018, COS 1995).
  • Climate: SMHI3 climate model, RCP 4.5 emissions pathway.
  • Hydrological observations: Portuguese Water Resources Information System (SNIRH).
  • Soil: European Soil Database (ESDAC ROO map).
  • Eucalyptus suitability: Site index map (Phuong, 2021).
  • Economic: Agricultural and forestry market price data (ESTAT), national economic coefficients (Eurostat), reservoir-elevation data (www.barragens.pt), accommodation inventory, consumer surplus data (Börger et al., 2021; Loomis and Bair, 2023), constructed wetland cost and design parameters (Kok et al., 2025; La Notte et al., 2017).

Main Results

• Streamflow: Afforestation effects on streamflow are modest compared to climate change. EUCINT reduces mean annual inflow to Montargil by 9% (current climate) and 7% (future), with no net decline for Maranhão. RESTOAK increases annual inflows by approximately 1% in both reservoirs. Climate change alone projects a 29% reduction in mean annual inflows by 2041–2070.
• Sediment Loads: Land cover change significantly impacts sediment loads. EUCINT increases sediment inflow to Montargil by 85–185% and Maranhão by 11–47%. RESTOAK reduces sediment loads in both reservoirs by 11–47%.
• Phosphorus Loads: Land cover change strongly influences phosphorus dynamics. Both EUCINT and RESTOAK substantially reduce annual total phosphorus (TP) loads (EUCINT: 26–69% reduction; RESTOAK: 33–75% reduction) and concentrations in the reservoirs, with Maranhão even falling below the good ecological status threshold under current climate conditions for both scenarios.
• Economic Impacts (Present Value 2025–2070, € million):
  • Net land-use returns: EUCINT results in a loss of -6,388 € million; RESTOAK generates a gain of +23,849 € million.
  • Reservoir sediment management costs: EUCINT leads to increased costs of -228 € million; RESTOAK results in avoided costs of +152 € million.
  • Water purification: Both scenarios show benefits: EUCINT +275 € million; RESTOAK +195 € million.
  • Irrigation water availability: EUCINT shows a minor loss of -1 € million; RESTOAK a minor gain of +4 € million.
  • Water-based recreation: EUCINT results in a loss of -18 € million; RESTOAK a gain of +12 € million.
  • Total Balance: EUCINT results in a net loss of -6,360 € million; RESTOAK yields a substantial net gain of +24,212 € million.
• Sensitivity Analysis: The total economic balance is most sensitive to assumptions regarding cork oak productivity and market prices. RESTOAK consistently shows a positive balance across all tested assumptions, while EUCINT generally maintains a negative balance.

Contributions

This study provides an integrated hydrological-economic assessment framework that explicitly quantifies basin-scale ecosystem service trade-offs of upstream afforestation, demonstrating how outcomes depend on biophysical conditions, species choice, and management. It offers a practical basis for comprehensive assessment of nature-based solutions, informing integrated river basin management under climate change, and strengthening the economic rationale for investments in line with EU Water Framework Directive and Nature Restoration Plans by avoiding scope bias in appraisal.

Funding

This work was supported by the MERLIN project, funded by European Union’s Horizon 2020 research and innovation programme grant agreement (101036337).

Citation

@article{Kok2026Ecosystem,
  author = {Kok, S. and Hein, L. and Clec'h, S. Le and Nunes, J.P. and Glavan, M.},
  title = {Ecosystem service trade-offs of upstream afforestation: an integrated hydrological-economic assessment in the Sorraia basin, Portugal},
  journal = {Frontiers in Environmental Science},
  year = {2026},
  doi = {10.3389/fenvs.2026.1838037},
  url = {https://doi.org/10.3389/fenvs.2026.1838037}
}