Abstract
Flooding is the most widespread hydrological hazard worldwide that affects water management, nature protection, economic activities, hydromorphological alterations on ecosystem services, and human health. The mitigation of the risks associated with flooding requires a certain management of flood zones, sustained by data and information about the events with the help of flood maps with sufficient temporal and spatial resolution. This paper presents the potential use of the Sentinel-1 SAR (Synthetic Aperture Radar) images as a powerful tool for flood mapping applied in the event of extraordinary floods that occurred during the month of April 2018 in the Ebro (Spain). More specifically, in this study, we describe accurate and robust processing that allows real-time flood extension maps to be obtained, which is essential for risk mitigation. Evaluating the different Sentinel-1 parameters, our analysis shows that the best results on the final flood mapping for this study area were obtained using VH (Vertical-Horizontal) polarization configuration and Lee filtering 7 × 7 window sizes. Two methods were applied to flood maps from Sentinel-1 SAR images: (1) RGB (Red, Green, Blue color model) composition based on the differences between the pre- and post-event images; and (2) the calibration threshold technique or binarization based on histogram backscatter values. When comparing our flood maps with the flood areas digitalized from vertical aerial photographs, done by the Hydrological Planning Office of the Ebro Hydrographic Confederation, the results were coincident. The result of the flooding map obtained with the RADAR (Radio Detection and Ranging) image were compared with the layers with different return periods (10, 50, 100, and 500 years) for a selected zone of the study area of SNCZI (National Flood Zone Mapping System in Spain). It was found that the images are consistent and correspond to a flood between 10 and 50 years of return. In view of the results obtained, the usefulness of Sentinel-1 images as baseline data for the improvement of the methodological guide is appreciated, and should be used as a new source of input, calibration, and validation for hydrological models to improve the accuracy of flood risk maps.
Highlights
A river flood occurs when the river flow can no longer be contained within its bed, and over spills its banks
A functional methodology was proposed for flood monitoring at a necessary spatial resolution derived from Synthetic Aperture Radar (SAR) images
It aimed to highlight the potential use of the Sentinel-1 SAR data sets of the European Earth Observation mission for flood monitoring occurring in the middle course of the Ebro River (Spain) in April 2018
Summary
A river flood occurs when the river flow can no longer be contained within its bed, and over spills its banks. Extreme flooding is a hydrological event that affects water management, conservation efforts, economic activities, hydromorphological alterations on the ecosystem services, and human health It presents a large number of technical challenges in terms of efficient management and public policy worldwide [5]. When major progressive flooding occurs, it is essential to delimit the affected areas, and to be able to assess the damage caused, in order to provide a “ground truth” of great interest for better empirical knowledge of the water environment. These accurate mappings of the flooded areas are needed when monitoring and evaluating the status, impact, and effectiveness of efforts [7].
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