Flooding vulnerability in Algiers (Algeria): An Analytic Hierarchy Process

Abstract

Flooding is the second most serious hazard in Algeria, after earthquakes. According to the Civil Protection Services census, the department of Algiers experienced 174 floods between 1946 and 2021, several devastating floods. This study examines Algiers’ vulnerability to flooding using the Hierarchical Multicriteria Analysis (AHP) method, which aggregates eight criteria: altitude distribution, slopes, drainage density, topographic wetness index, land cover and land use, normalized difference vegetation index, soil types, and precipitations. With an accuracy of 85%, the resulting vulnerability map is an essential tool for better risk and land use management. The municipalities most vulnerable to flooding are located in the Mitidja (east of Algiers) and Algiers’ Western Sahel. These areas cover 71.29 km2 (10% of Algiers’ area) and are primarily located in the watersheds of El Harrach, El Hamiz, and Reghaia, while 25.8% of urbanized areas are moderately vulnerable. However, these areas require special attention because of their high population density. Flood risk has undeniably become more frequent and intense due to Algiers’ significant and often anarchic increase in urbanization in recent years, particularly at the edge of the major Wadis beds (nearly half of their watershed area is urbanized). This trend will worsen as extreme weather events increase, necessitating a stricter application of land use planning regulations and prevention, adaptation, and mitigation measures.