Oerlemans et al. (2025) Flood exposure in Rotterdam's unembanked areas from 1970 to 2150: sensitivities to urban development, sea level rise, and adaptation

Identification

• Journal: Natural hazards and earth system sciences
• Year: 2025
• Date: 2025-10-14
• Authors: Cees Oerlemans, M. van den Boomen, Ties Rijcken, M. Kok
• DOI: 10.5194/nhess-25-3921-2025

Research Groups

• Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, the Netherlands
• Risk and Disaster Management, HKV, Lelystad, the Netherlands
• Centre of Expertise HRTech, Rotterdam University of Applied Sciences, Rotterdam, the Netherlands

Short Summary

This study quantifies historical (1970-2020) and projected (to 2150) residential flood exposure in Rotterdam's unembanked areas, attributing changes to urban development, sea level rise, and the Maeslant storm surge barrier. It finds that without further adaptation, flood exposure is projected to increase significantly by 2150, primarily driven by sea level rise, despite the historical mitigating effect of the Maeslant barrier.

Objective

• To analyze the historical (1970–2020) evolution and future projections (to 2150) of extreme water level hazards and urban development in Rotterdam’s unembanked areas under low- (RCP2.6) and high-emission (RCP8.5) scenarios.
• To determine the historical (1970–2020) and projected (to 2150) trajectory of total residential flood exposure in Rotterdam’s unembanked areas, considering sea level rise, planned urban development, and the Maeslant storm surge barrier’s construction.
• To investigate the spatial variation of flood exposure across different unembanked neighborhoods and its temporal changes.
• To quantify the relative contributions of urban development, sea level rise, and the Maeslant storm surge barrier to changes in flood exposure from 1970 to 2150.
• To assess the sensitivity of future flood exposure to different design flood elevation policies for new urban developments.

Study Configuration

• Spatial Scale: Rotterdam's unembanked areas, located in the Rhine–Meuse delta, Netherlands, focusing on 14 specific neighborhoods.
• Temporal Scale: Historical analysis from 1970 to 2020, and future projections from 2020 to 2150. Urban development data extends to 2040.

Methodology and Data

• Models used:
  • WAQUA (2D hydrodynamic model, part of WBI2017 dataset) for hydrodynamic simulations.
  • Hydra-NL (v.2.8.2, open-source probabilistic model) for translating hydrodynamic computations into water level frequency lines.
• Data sources:
  • WBI2017 dataset (official governmental dataset) for flood hazard.
  • KNMI’23 climate change scenarios (RCP2.6 and RCP8.5) for future sea level rise projections.
  • Sea Level Rise Monitor 2022 (Deltares, 2023) for historical local sea level rise trends (1.8 mm/year for 1970–1990 and 2.9 mm/year for 1990–2020).
  • BAG dataset (Kadaster, 2022) for existing residential building footprints and attributes.
  • Digital terrain model of the Netherlands (AHN3, 0.5 m resolution raster) for ground-level elevation data.
  • Planned urban development data from the Municipality of Rotterdam (Gemeente Rotterdam, 2023) for future housing units up to 2040.

Main Results

• Without additional adaptation, residential flood exposure in Rotterdam’s unembanked areas is projected to increase significantly, particularly in the 22nd century under the high-emission (RCP8.5) scenario.
• Under RCP8.5, exposure for 10-year flood events is projected to increase 7-fold by 2150 compared to 2020 (from 800 to 5700 houses). For 100-year events, a 6-fold increase (from 1600 to 9100 houses), and for 1000-year events, an 8-fold increase (from 4700 to 39400 houses).
• Under the low-emission (RCP2.6) scenario, 10-year and 100-year events project a 3-fold increase, and 1000-year events a 2-fold increase by 2150 compared to 2020.
• The Maeslant storm surge barrier, operationalized in 1997, significantly reduced historical flood exposure, decreasing exposed houses by approximately 62% for 100-year events and 67% for 1000-year events compared to 1996 levels.
• By 2150 under RCP8.5, 1000-year flood levels are projected to approach pre-barrier conditions, indicating that the barrier in its current configuration does not offer indefinite protection against long-term sea level rise.
• Flood exposure varies considerably across Rotterdam’s 14 unembanked neighborhoods, with Nieuwe Werk, Heijplaat, and Noordereiland projected to face disproportionately high exposure rates (exceeding 65% for 100-year events by 2150 under RCP8.5).
• Attribution analysis reveals that the Maeslant barrier had the largest historical impact on decreasing exposure. For future projections, sea level rise is the primary driver of increasing exposure, outweighing the impact of planned urban development under current design flood elevation policies.
• The current design flood elevation policy of NAP +3.6 m for new constructions effectively reduces their future exposure. Raising this standard to NAP +3.8 m offers incremental benefits, primarily delaying exposure to very extreme, late-century events by approximately 30 years.

Contributions

• Developed and applied a structured and flexible assessment framework to analyze historical, present, and future residential flood exposure in unembanked urban areas.
• Provided a detailed, long-term (1970–2150) quantification of flood exposure in Rotterdam’s unembanked areas, explicitly attributing changes to urban development, sea level rise, and the Maeslant storm surge barrier.
• Offered a granular, neighborhood-level analysis of flood exposure, highlighting spatial heterogeneity and the need for tailored adaptation strategies, which refines broader-scale flood risk assessments.
• Extended the temporal scope of flood risk assessments beyond 2100, addressing a gap in existing literature and informing longer-term urban planning and water management decisions.
• Utilized detailed object-level building data (BAG dataset) for residential assets, providing higher precision for exposure assessment compared to studies using broader land use classifications.

Funding

• Project RED and BLUE, Real Estate Development and Building in Low Urban Environments (project number NWA.1389.20.224)
• Dutch Research Agenda (NWA)
• Dutch Research Council (NWO)

Citation

@article{Oerlemans2025Flood,
  author = {Oerlemans, Cees and Boomen, M. van den and Rijcken, Ties and Kok, M.},
  title = {Flood exposure in Rotterdam's unembanked areas from 1970 to 2150: sensitivities to urban development, sea level rise, and adaptation},
  journal = {Natural hazards and earth system sciences},
  year = {2025},
  doi = {10.5194/nhess-25-3921-2025},
  url = {https://doi.org/10.5194/nhess-25-3921-2025}
}