Analysis of extreme climatic phenomena in northern Algeria

Within the framework of climate change, droughts and flooding have significant societal and environmental ramifications, which prompts research into management strategies, associated risks, and resulting crises. This study aims to demonstrate the historical occurrence of droughts and inondations and their effects on agriculture and the environment. In order to implement various countermeasures, such as early warning systems in the event of an outbreak or drought, surveillance, and emergency planning, indices that are now invaluable tools were used. These indices constitute a practical way to turn large amounts of data into quantitative information for applications like forecasting droughts and flooding, communicating the severity of these phenomena, and raising public awareness of the potential consequences of droughts and flooding. The public’s increased awareness of these implications and anticipated consequences is the study's social advantage. Our study is based on the analysis of the impact of temperature and precipitation on extreme drought and flooding in the Wadi Lakhdar watershed located in northwest Algeria. We performed calculations to assess extreme droughts using the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) at different time scales (1, 3, 6, 9, 12 and 24 months). Applying the SPI drought indices and SPEI shows that the wet years were 1972, 1978, 1997, 1998, 2009, 2010, 2013 and 2014 and the dry years were 1982, 1983, 1984, 1988, 1989, 1990, 1995, 1999, 2000, 2001, 2005, 2006, 2007, 2020 and 2021. Subsequently, 33 extreme floods were studied (6 in autumn; 9 in winter; 18 in spring and 3 in summer) and it is obvious that floods autumn and spring present risk than floods winter and summer. The 18 spring floods, which represent 54% of the floods over a period of 52 years, are the most important compared to other seasons, with high flows and water levels, which can reach successive maximum values of 138 m 3 /s and 2.5 m recorded on March 29, 1973. Furthermore, the 6 autumn floods, which represent 18% of the total floods, can reach maximum values of 2.48 m for the water height and 138.2 m 3 / s for flow. Furthermore, the 9 winter floods and 3 summer floods, which respectively represent 27% and 9% of the total floods, do not present a significant trend, with the exception of the winter flood recorded on January 25,26, 2013, with a flow of 37.8 m 3 /s and a water depth of 1.31 m.