Résumés
Résumé
L’urbanisation rapide et non maîtrisée dans les zones basses de Pikine et Keur Massar, deux départements du Sénégal, a fortement accru la susceptibilité et l’exposition aux inondations récurrentes. Dans ce contexte, la cartographie de la susceptibilité aux inondations constitue un outil stratégique pour la planification urbaine et la réduction des risques. Cette étude vise à élaborer une carte de susceptibilité aux inondations dans les départements de Pikine et de Keur Massar, au Sénégal, en combinant l’analyse multicritère (AHP) avec des outils de Système d’Information Géographique (SIG). Six facteurs déclencheurs ont été intégrés : la pluviométrie, l’élévation, la pente, la densité de drainage, le type de sol et l’occupation du sol. Les pondérations des critères ont été établies selon la méthode de Saaty, et la carte finale a été obtenue par superposition pondérée. Les données satellitaires Landsat-8 et SRTM, analysées via Google Earth Engine, ont permis de cartographier les zones inondées sur la période 2015-2024, subdivisée en trois sous-périodes. L'indice de différence normalisée modifiée de l’eau (MNDWI) a été utilisé pour détecter les inondations, tandis que l’indice de végétation par différence normalisée (NDVI) a permis d’éliminer les faux positifs liés à la végétation. La carte de fréquence des inondations a ensuite servi à valider la carte de susceptibilité. Les résultats indiquent que 56,60 % de la superficie des départements de Keur Massar et Pikine présentent une susceptibilité élevée à très élevée. En croisant ces données avec les infrastructures, il apparaît que 67,46 % des bâtiments et plus de la moitié du réseau routier et ferroviaire sont fortement inondables. Ces vulnérabilités s’expliquent par une urbanisation non planifiée dans des zones basses, jadis réservées à la rétention d’eau. L’étude souligne l’urgence d’une gestion territoriale intégrée et résiliente.
Mots-clés :
- susceptibilité,
- inondations,
- analyse par procédé hiérarchique (AHP),
- Système d’Information Géographique (SIG),
- Google Earth Engine (GEE)
Abstract
Rapid and unplanned urban expansion in low-lying zones of Pikine and Keur Massar has significantly increased flood susceptibility and exposure. In response, flood susceptibility mapping is a strategic tool for urban planning and risk reduction. This study aims to produce a flood susceptibility map for the departments of Pikine and Keur Massar in Senegal, by combining Analytical Hierarchy Process (AHP) with Geographic Information Systems (GIS) . Six triggering factors were integrated: rainfall, elevation, slope, drainage density, soil type, and land use. Weighting of the criteria was based on the Saaty method, and the final map was generated through weighted overlay analysis. Landsat-8 and SRTM satellite data, processed via Google Earth Engine, were used to map flooded areas over the period 2015–2024, divided into three sub-periods. The Modified Normalized Difference Water Index (MNDWI) was used to detect flood, while the NDVI helped reduce false detections due to vegetation. The flood frequency map served to validate the AHP-based susceptibility results. Findings show that 56.60% of the study area’s surface exhibits high and very high susceptibility. By overlaying this data with infrastructure layers, the study reveals that 67.46% of buildings and more than half of the road and railway networks are highly flood-prone. This exposure is largely due to unplanned urban expansion into former water retention basins. The results underscore the urgent need for integrated and resilient spatial planning strategies to mitigate the growing flood risks in these densely urbanized areas. The approach provides a replicable framework for flood risk assessment and infrastructure vulnerability analysis in similar contexts.
Keywords:
- susceptibility,
- floods,
- Analytic Hierarchy Process (AHP),
- Geographic Information Systems (GIS),
- Google Earth Engine (GEE)
Parties annexes
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