The Application of Remote Sensing and GIS Tools in Mapping of Flood Risk Areas in the Souss Watershed Morocco

Abstract

The Souss watershed in the Souss-Massa region of Morocco is dominated by a semi-arid climate. The rainfall pattern is highly variable with frequent droughts and floods. The changing climatic conditions and the ongoing trends of overexploitation of water resources exacerbated the frequency and intensity of these climate hazards. The changing hazard characteristics have a significant impact on the communities who largely depend on agriculture, tourism and fishing activities. Detailed characterization of hazard risks is the first step for management of risks associated with climate extremes and optimal use water resources. This study presents a comprehensive methodology for mapping of flood risk areas to support decision-making in relation to flood hazard risk management, including flood prevention and preparedness. The methodology employs a multicriteria analysis in a GIS environment for identification of vulnerable flood-prone areas. The methodology involves combination of several thematic maps representing the most determining factors of flooding. The factors include geographic (elevation, slope, curvature, lithology) biophysical (land use, Normalized Difference Vegetation Index-NDVI) and hydrological (rainfall, stream density, stream power index, topographic wetness index) features. The weighted values of the parameters were used for mapping based on their relative importance for flood occurrence and severity. With the weighted values, the maps of the above parameters were overlaid and flood hazard maps were produced. The resulting maps were used to divide the watershed into five flood severity regions. The historical flood event data from the Souss-Massa Draa Hydraulic Basin Agency (ABHSMD) was used to validate the reliability of the flood hazard maps. The results showed that the parameters selected for mapping capture the variability of flood risks and could be used for planning and decision-making for both flood risk and water resources management.