Tügel et al. (2025) Extreme precipitation and flooding in Berlin under climate change and effects of selected grey and blue-green measures

Identification

• Journal: Natural hazards and earth system sciences
• Year: 2025
• Date: 2025-11-26
• Authors: Franziska Tügel, Katrin M. Nissen, Lennart Steffen, Yangwei Zhang, Uwe Ulbrich, Reinhard Hinkelmann
• DOI: 10.5194/nhess-25-4673-2025

Research Groups

• Chair of Water Resources Management and Modeling of Hydrosystems, Technische Universität Berlin, Berlin, Germany
• Institute for Meteorology, Freie Universität Berlin, Berlin, Germany
• Department of Water Resources, Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede, the Netherlands
• Multidisciplinary Water Management, Civil Engineering and Management, Faculty of Engineering Technology, University of Twente, Enschede, the Netherlands

Short Summary

This study quantifies the projected increase in extreme precipitation in Berlin under climate change (RCP8.5) and its impact on urban flooding, demonstrating that a 46 % increase in 1 h 100-year rainfall leads to a 51 % increase in maximum water depth. It further assesses the effectiveness of grey infrastructure, infiltration, and retention roofs in mitigating these impacts, highlighting the non-linear relationship between rainfall and flooding and the need for combined adaptation strategies.

Objective

• To quantify potential changes in extreme precipitation under climate change scenarios in Berlin, Germany, and their resulting impacts on urban flooding in a selected flood-prone area.
• To investigate the effectiveness of the existing drainage system, infiltration from unsealed surfaces, and retention roofs during extreme rainfall events under both current and future climate conditions.
• To address uncertainties in infiltration by varying soil hydraulic conductivity and the degree of surface sealing.

Study Configuration

• Spatial Scale: City of Berlin, Germany, with a focus on a 13 km² flood-prone area around the Gleimtunnel in Central Berlin. Hydrodynamic model uses 5 m rectangular cells.
• Temporal Scale: Three 30-year periods for climate simulations (1971–2000 historical, 2031–2060 RCP8.5, 2071–2100 RCP8.5). Hydrodynamic simulations use 1 h duration rainfall events over a 2 h total simulation time.

Methodology and Data

• Models used:
  • Climate model: COSMO-CLM (CCLM-CPS) at convection-permitting resolution (approximately 3 km).
  • Hydrodynamic models: hms++ (2D shallow water model) bi-directionally coupled with SWMM (1D Storm Water Management Model) for drainage.
  • Statistical analysis: Duration-dependent general extreme value distribution (d-GEV) for return level estimation.
• Data sources:
  • Climate simulations: CCLM-CPS (forced by MIROC5 global climate model).
  • Meteorological observations: KOSTRA-DWD (German Weather Service) for statistical extreme precipitation intensities.
  • Digital elevation model: ATKIS® DGM Berlin (1 m spatial resolution).
  • Building data: Geoportal Berlin.
  • Land use data: Geoportal Berlin.
  • Saturated hydraulic conductivity: Umweltatlas Berlin.
  • Surface sealing degrees: Umweltatlas Berlin.
  • Drainage system model: Berliner Wasserbetriebe (BWB).

Main Results

• Under RCP8.5 conditions, the 1 h rainfall sum for a 100-year return level is projected to increase by 46 % for 2031–2060 compared to the historical period (1971–2000). The strongest hourly intensity across all simulated periods increases by 123 %.
• For the future 100-year event, maximum water depth in the Gleimtunnel area increases by 51 %, maximum surface runoff by 43 %, and combined sewer overflow (CSO) volume by 33 %. For the strongest event, these increases are 137 %, 296 %, and 74 %, respectively.
• The existing drainage system significantly reduces flooding; neglecting it results in a 170 % increase in maximum water depth at the Gleimtunnel for the historical 100-year event, though its effectiveness decreases with higher rainfall intensity.
• Infiltration significantly reduces flooding; neglecting it increases maximum water depth at the Gleimtunnel by 33 % for the historical 100-year event and CSO volume by 19 %–30 %.
• Replacing all roofs with retention roofs (best-case scenario) reduces maximum water depth at the Gleimtunnel by 22 %–24 % and CSO volume by 15 %–20 %, also reducing surface runoff below the pedestrian stability threshold (0.22 m²/s) during the strongest event.
• Flood volumes increase non-linearly with rainfall sums; for the strongest event, flood volume increases by 189 % (after 30 min) and 219 % (after 120 min) compared to the historical 100-year event.
• The temporal distribution of rainfall is crucial; constant rainfall events produce 51 %–54 % smaller flood volumes at peak time compared to Euler-2 design rainfalls.
• Ranking of influencing factors on flood volume after 120 min (Historical 100a event): (1) Infiltration, (2) Drainage, (3) Retention roofs, (4) Temporal rainfall distribution.

Contributions

• Quantifies the local impacts of climate change on extreme precipitation and urban flooding in Berlin using a high-resolution, convection-permitting climate model and a bi-directionally coupled 2D-1D hydrodynamic model.
• Provides a systematic assessment of the effectiveness of both grey infrastructure (drainage system) and blue-green measures (infiltration, retention roofs) under current and future extreme rainfall scenarios.
• Highlights the non-linear relationship between increased rainfall intensity and flood severity, emphasizing the importance of temporal rainfall distribution.
• Addresses uncertainties in infiltration parameters, demonstrating its significant role even in highly urbanized areas.
• Underscores the urgent need for climate-aware urban flood risk maps and the implementation of combined, multi-functional mitigation strategies to adapt to increasing flood risks.

Funding

• Einstein Research Unit “Climate and Water under Change” of the Einstein Foundation Berlin and Berlin University Alliance (grant number ERU-2020-609).
• Open Access Publication Fund of TU Berlin.
• Deutsches Klimarechenzentrum (DKRZ) (project ID 1229).
• NHR Center NHR@ZIB (supported by the Federal Ministry of Education and Research and participating state governments).

Citation

@article{Tügel2025Extreme,
  author = {Tügel, Franziska and Nissen, Katrin M. and Steffen, Lennart and Zhang, Yangwei and Ulbrich, Uwe and Hinkelmann, Reinhard},
  title = {Extreme precipitation and flooding in Berlin under climate change and effects of selected grey and blue-green measures},
  journal = {Natural hazards and earth system sciences},
  year = {2025},
  doi = {10.5194/nhess-25-4673-2025},
  url = {https://doi.org/10.5194/nhess-25-4673-2025}
}