Environmental Technology Research Reveals Insights into Extreme Flooding Mechanisms

A recent study on environmental technology has provided new information on the mechanisms behind extreme flooding events. In mid-July 2021, a quasi-stationary extratropical cyclone over western Germany and eastern Belgium led to sustained widespread precipitation, nearly doubling monthly rainfall amounts in less than 72 hours. The resulting extreme flooding in the Eifel-Ardennes low mountain range river catchments resulted in loss of lives and substantial damage. Researchers from the Institute of Biosciences and Geosciences have used a numerical laboratory approach to simulate the event using the integrated hydrological surface-subsurface model ParFlow.

Key Takeaways:

• The quasi-stationary extratropical cyclone led to unprecedented sustained widespread precipitation, almost doubling monthly rainfall amounts in less than 72 hours.
• The event resulted in extreme flooding in the Eifel-Ardennes low mountain range river catchments, causing loss of lives and substantial damage.
• The numerical laboratory approach using ParFlow was able to reproduce the timing and order of magnitude of the flood event without additional calibration or tuning.
• The soil buffer capacity played a significant role in the flood event, with the upper soil able to buffer between one third to half of the precipitation that does not contribute immediately to the streamflow response.
• In the case of the Vesdre river catchment, the initially higher soil water saturation levels resulted in a lower buffering capacity, leading to more precipitation being transferred into discharge.
• The study highlights the prognostic capabilities of ParFlow and its ability to explore the physical mechanisms of extreme flooding events.
• The research was conducted by a team of researchers from the Institute of Biosciences and Geosciences, led by Klaus Goergen, with additional authors Alexandre Belleflamme, Suad Hammoudeh, Jan Vanderborght, and Stefan Kollet.
• The study suggests that explicit consideration of soil buffer capacities is crucial for accurate forecasting of flood events, particularly in regions with high precipitation variability.

Statistics:

• 52-member spatially and temporally consistent high-resolution hindcast reconstruction of the event.
• 72 hours: the time it took for the precipitation to nearly double monthly rainfall amounts.
• 1/3 to 1/2: the proportion of precipitation that was buffered by the upper soil in the highly affected river catchments.
• 30%: the reduction in water balance deficit in the Ahr, Erft, and Kyll river catchments when including the soil buffer capacity in the model.
• 1.5: the factor by which the ParFlow simulations increased the critical zone infiltration velocities.

Sources:

• The July 2021 flood event in the Eifel-Ardennes mountains as simulated by the high-resolution integrated hydrologic model ParFlow. Frontiers in Water, 2025,7.
• doi-org.sdpl.idm.oclc.org/10.3389/frwa.2025.1571704
• Klaus Goergen, Institute of Biosciences and Geosciences (IBG-3, Agrosphere), Forschungszentrum Julich, Julich, Germany.