Mapping drought characteristics in northern Algerian Basins using the ERA5-Land dataset

Over the past decades, drought events have led to significant agricultural losses and water shortages in the Algerian catchments; these hydro-meteorological phenomena strongly affect the entire Mediterranean region, and its frequency and intensity may increase due to climate change. The purpose of this study is to investigate drought conditions in the northern region of Algeria using the standardized precipitation index (SPI) at different monthly scales (3, 6, 12, 24 months), calculated through the ERA5-Land monthly dataset, which provides a much more detailed mapping of drought vulnerability across the country compared to observed rain gauge data, whose ground distribution is sparse and whose data archive is neither homogeneous nor complete for the study area. The main characteristics of drought events (e.g., quantity, duration, severity, and intensity), that have historically affected several hydrological basins in the northern part of the nation, are examined using the run theory applied to SPI values from 1950 to 2022. Although a high number of occurrences appear at shorter timescales, the results indicate that these episodes generally have shorter durations and lower severity compared to long-timescale droughts. Specifically, a decrease in the average number of drought events as the timescale increases is found: from 69 events for the 3-month SPI, with an average duration of about 2 months, to 17 events for the 24-month SPI, with an average duration of approximately 8 months. By analysing the spatial and temporal distribution of drought features, this approach aims to identify areas experiencing water stress and support more effective water management and mitigation strategies.