Integration of Remote Sensing and Hydraulic Modeling for Dynamic Flood Monitoring: A Copernicus Emergency Management Service for retrospective flood temporal analysis in Saarland, Germany

Floods affect many regions of the world every year and are the most deadly natural hazard. The increasing pressures of a growing global population, widespread ecosystem degradation, and the compounding effects of climate variability and change are significantly increasing flood risks worldwide. Hydrodynamic models, combined with Earth Observations (EO), play an increasingly important role in the comprehensive analysis and characterization of floods, providing a deeper understanding of their dynamics in past, present, and future scenarios.

Under the “Copernicus Emergency Management Service (CEMS) Risk and Recovery Mapping (RRM)” framework, this on-call study (i.e., CEMS activation “ΕMSN: Retrospective flood temporal analysis of floods in Saarland, Germany”) focused on the mid-May 2024 (16/05/2024-22/05/2024) flood in Saarland, Germany, which resulted in extensive damage across the Saarland state capital Saarbrücken and several districts in Saarland. Leveraging advancements in Earth observation (EO), this study integrated multi-source remote sensing data into a 2D hydraulic modeling framework to enhance the understanding of flood dynamics in the region through a comprehensive temporal analysis.

Using the HEC-RAS hydraulic modeling open-source software of the United States Army Corps of Engineers (USACE), a rain-on-grid approach was employed to simulate direct rainfall runoff to supplement fluvial model simulation of flood propagation over a 7-day period. Model calibration was based on observed water depth data from Gauging stations’ recordings, with adjustments made to improve accuracy. Validation was conducted using EO-derived flood delineations from multitemporal post-event imagery, spanning multi-Platform Satellite products including SAR (Sentinel-1A, RadarSat-2, COSMO-SkyMed and TerraSAR-X) and Optical (Planet Scope) imagery. Therefore, the outputs of the study including the water depth and the flood persistence were derived from the combination of the hydraulic modeling and remote sensing methodologies.

Despite the relatively lower flood thematic accuracy of EO-derived flood outlines in urban and forested areas given the inherent limitations of the SAR analysis techniques, the availability of multitemporal EO imagery was decisive in validating the hydraulic modelling accuracy and robustness. The study findings emphasize the emerging potential of EO data for validating hydraulic models and therefore enhancing flood mapping and monitoring capabilities. In this context, the availability of multitemporal EO datasets further enhanced the flood modelling performance in providing a better insight into the flood propagation and dynamics over the whole period of impact.

Acknowledgment: The service took place under the Framework Service Contract 945236–IPR–2023 “Copernicus Emergency Management Service (CEMS) Risk and Recovery Mapping (RRM) Tailor-Made Products. 

We would like to acknowledge the great support of the JRC CEMS team memebrs, namely Guido Di Carlo, Cristina Rosales Sanchez, and Emanuele Sapino, for the completion of this service contract.