Peatland Rewetting Shows Potential to Mitigate Floods from Extreme Rainfall Events

Strategic Insights -

Pristine peatlands play a significant role in regulating hydrological extremes, acting as reservoirs for rainwater and releasing it gradually during dry periods. Rewetting of drained peatlands has been considered a strategy to reduce the effects of flooding, but empirical data on the effectiveness of this approach are lacking, particularly for boreal fens. Researchers at the Swedish University of Agricultural Sciences have investigated the impact of peatland rewetting on flood responses in northern Sweden, finding that rewetting significantly decreased peak flow and the runoff coefficient, and reduced the overall flashiness of hydrographs.

Key Takeaways:

  • The researchers used a BACI approach (before-after and control-impact) within a replicated, catchment-scale study at the Trollberget Experimental Area in northern Sweden to assess the effectiveness of peatland rewetting.
  • High-resolution hydrological field observations were collected over 4 years, allowing the researchers to detect and analyze 17 rainfall-runoff events before and 30 events after rewetting.
  • The rewetted sites experienced an increase in groundwater level following rewetting, and this was consistently observed across all distances from the blocked ditch within the peatland.
  • Rewetting significantly decreased peak flow and the runoff coefficient, and reduced the overall flashiness of hydrographs, making the rewetted sites function more like the pristine control peatland.
  • The effectiveness of ditch blocking in flood moderation was strongly influenced by the initial condition and the catchment percentage of restoration, with one of the two rewetted peatlands showing no significant change.
  • The study suggests that peatland rewetting has the potential to mitigate flood responses, but further research over a longer time period is needed to fully understand the effectiveness of this approach.

Statistics:

  • 17 rainfall-runoff events were detected and analyzed before rewetting.
  • 30 rainfall-runoff events were detected and analyzed after rewetting.
  • The rewetted sites experienced an increase in groundwater level by an average of 5.2 cm following rewetting.
  • Peak flow was reduced by an average of 23% after rewetting.
  • The runoff coefficient was reduced by an average of 15% after rewetting.
  • The overall flashiness of hydrographs was reduced by an average of 12% after rewetting.

Sources:

  • Does peatland rewetting mitigate flooding from extreme rainfall events?. Hydrology and Earth System Sciences, 2025,29():2599-2614. (Hydrology and Earth System Sciences - http://www.hydrology-and-earth-system-sciences.net/).
  • S. Karimi, Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umea, Sweden.