Johary R. auteur aut IRD Révillion C. auteur aut IRD Catry Thibault auteur aut IRD Alexandre Cyprien auteur aut IRD Mouquet Pascal auteur aut IRD Rakotoniaina S. auteur aut IRD Pennober Gwenaelle auteur aut IRD Rakotondraompiana S. auteur aut IRD text journalArticle eng text/pdf reformatted digital access This paper presents an operational approach for detecting floods and establishing flood extent using Sentinel-1 radar imagery with Google Earth Engine. The methodology relies on change detection, comparing pre-event and post-event images. The change-detection method is based on the normalised difference ratio. Additionally, the HAND model is employed to delineate zones for processing only in flood-prone areas. The approach was tested and calibrated at a small scale to optimise parameters. In these calibration tests, an accuracy of 85% is achieved. The approach was then applied to the whole of the island of Madagascar after Cyclone Batsirai in 2022. The proposed method is enabled by the computing power and data availability of Google Earth Engine and Google Colab. The results show satisfactory accuracy in delineating flooded areas. The advantages of this approach are its rapidity, online availability and ability to detect floods over a wide area. The approach relying on Google Tools thus offers an effective solution for generating a large-scale synoptic picture to inform hazard management decision making. However, one of the method's drawbacks is that it depends to a large extent on frequent radar imagery being available at the time of flood events and on free access to the platform. These drawbacks will need to be taken into account in an operational scenario. specialized flood radar imagery Sentinel-1 Google Earth Engine Python MADAGASCAR 062 126 021 15 22 5368 [19 ] 2023 https://www.documentation.ird.fr/hor/fdi:010088785 10.3390/rs15225368 [F B010088785] https://www.documentation.ird.fr/hor/fdi:010088785 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2024-01/010088785.pdf IRD - Base Horizon / Pleins textes 2024-01-12 2025-02-24 fdi:010088785 fre