Elenius et al. (2025) Where can rewetting of forested peatland reduce extreme flows? Model experiment on the hydrology of Sweden

Identification

• Journal: Hydrology and earth system sciences
• Year: 2025
• Date: 2025-09-11
• Authors: Maria Elenius, Charlotta Pers, Sara Schützer, Göran Lindström, Berit Arheimer
• DOI: 10.5194/hess-29-4307-2025

Research Groups

• Hydrological Research Unit, SMHI, Norrköping, Sweden
• FOI, Linköping, Sweden (present address for one author)

Short Summary

This study used a national hydrological model to investigate the impact of rewetting drained forested peatlands in Sweden on extreme water flows. It found that rewetting has a negligible effect on extreme flows in larger catchments (≥10 km²), but can significantly alter local runoff and groundwater levels in small streams draining only peatlands, with effects depending on pre-rewetting conditions and tree cover reduction.

Objective

• To clarify the potential impact of rewetting drained forested peatlands on extreme water flows in Sweden and to understand the main drivers behind the heterogeneous hydrological responses.

Study Configuration

• Spatial Scale: National scale across Sweden (450 000 km²), divided into approximately 40 000 sub-catchments with an average size of 10 km². A detailed study focused on the Motala Ström catchment (15 000 km²) in south-east Sweden, comprising 882 sub-catchments. Calculations were performed within up to 116 hydrological response units (HRUs) per sub-catchment.
• Temporal Scale: Simulations covered a 10-year period (2012–2021) following a 5-year initialization (2007–2011), with results provided at a daily time step.

Methodology and Data

• Models used: HYPE (Hydrological Predictions for the Environment) model, specifically the S-HYPE setup (version 2016i).
• Data sources:
  • National data set of ditches (Lidberg et al., 2023).
  • National land cover data NMD (Swedish Environmental Protection Agency, 2023) with 10 m resolution.
  • Soil-type data (including peat) from the Swedish Geological Survey (2024), with resolutions between 1:25000 and 1:750000.
  • Total soil depth from Daniels and Thunholm (2014).
  • Precipitation and temperature as meteorological forcing data.

Main Results

• Rewetting drained forested peatlands has a negligible impact on extreme discharge (minimum and maximum yearly flows) in catchments of 10 km² or larger, with changes typically less than 5%. This is attributed to the small proportion of drained forested peatlands (approximately 1% of Sweden's surface area) relative to other land cover types, leading to considerable mixing of runoff.
• For small streams draining only rewet peatlands, rewetting can have a substantial local impact on runoff and groundwater levels.
• Rewetting combined with reduced tree cover (Rewet2 scenario) often leads to significant increases in simulated low runoff (up to a factor of 10) in peatland-dominated streams, which can improve water security during droughts.
• Conversely, the Rewet2 scenario also generally results in increased high runoff (up to 3–6 mm d⁻¹) in these small streams, which is undesirable for flood management.
• Rewetting by ditch blocking alone (Rewet1 scenario) showed smaller and more variable impacts on runoff extremes; sometimes reducing low runoff if ditches were very active, and sometimes reducing high runoff.
• Minimum and maximum groundwater levels in rewet peatlands increased substantially, up to 0.7 m and 0.8 m respectively, with larger increases observed when tree cover was reduced.
• The groundwater level prior to rewetting and the extent of tree cover reduction are identified as major drivers governing the hydrological response to rewetting.

Contributions

• This study provides the first national-scale hydrological model experiment in Sweden to assess the impact of rewetting forested peatlands on extreme water flows.
• It clarifies that rewetting is not an effective measure for improving water security (reducing floods or increasing low flows) at larger catchment scales (≥10 km²).
• It identifies critical factors (pre-rewetting groundwater levels and tree cover density) that determine the variable hydrological responses of rewetting at local scales, particularly in streams draining only peatlands.
• The findings offer crucial guidance for policymakers on the effective allocation of resources for rewetting actions, distinguishing between large-scale water management and local ecosystem benefits.
• The study involved the development of new model capabilities for routing runoff between recharge and discharge hydrological response units (HRUs) to better represent landscape position.
• It integrated a recently published national dataset of drainage ditches into the hydrological modeling framework.

Funding

• Naturvårdsverket (grant nos. NV-01874-23 and NV-08138-18)
• Svenska Forskningsrådet Formas (grant no. FR-2022/0006)
• Swedish Research Council, Forte, Formas, and Vinnova (for publication)

Citation

@article{Elenius2025Where,
  author = {Elenius, Maria and Pers, Charlotta and Schützer, Sara and Lindström, Göran and Arheimer, Berit},
  title = {Where can rewetting of forested peatland reduce extreme flows? Model experiment on the hydrology of Sweden},
  journal = {Hydrology and earth system sciences},
  year = {2025},
  doi = {10.5194/hess-29-4307-2025},
  url = {https://doi.org/10.5194/hess-29-4307-2025}
}