Assessing flood dynamics in Algiers, Algeria: influence of land cover change and precipitation regimes

Recent climate change has altered global precipitation patterns, resulting in a variety of natural hazards, including flash floods, exacerbated by intensive land use and urbanization. This paper examines the spatiotemporal evolution of flooding in the Department of Algiers, focusing on two major causes: land cover and precipitation regimes and patterns. It investigates changes in land cover distribution between 1984 and 2022 using supervised classification techniques. The National Agency of Hydraulic Resources (ANRH) provided daily precipitation data from three meteorological stations over a 50-year period. Our findings show a significant increase in flood occurrences, from an average of two floods per year prior to 2006 to ten floods per year. This intensification can be attributed to the significant expansion of the urbanized area in Algiers, which increased from 18.89% in 1984 to 43.2% in 2022, with an annual growth rate of 2.92 km² to 9.68 km². Despite a decrease in annual precipitation totals and a reduction in heavy rainfall episodes due to climate change, flooding is becoming more common. Variations in rainfall patterns, particularly the intensity and duration of wet periods, play a significant role in flooding peaks, as evidenced by the extremely wet period at the end of the 2000s after a long dry spell. These findings can help civil protection and relevant authorities develop future flood risk prevention strategies.