Multi-scale analysis of drought events in Northern Algeria based on ERA5-Land SPI data

Drought poses significant environmental and socio-economic challenges in Mediterranean countries such as Algeria, where rain-fed agriculture dominates, and climate change exacerbates water scarcity. In this paper, an investigation of meteorological drought in Northern Algeria in the period 1950–2022 was carried out focusing on its spatiotemporal characteristics. The analysis focuses on drought events identification through the Standardized Precipitation Index (SPI), calculated at several timescales with the run theory methodology. Using the Copernicus Climate Change Service high-resolution ERA5-Land monthly data set, SPI values were computed across 3,983 grid points to derive key drought characteristics, including frequency, and maximum duration values, severity, and intensity. An additional analysis was carried out to detect possible temporal tendencies in the SPI across multiple time scales, ranging from short to long term. The findings reveal that while drought frequency remains relatively consistent across timescales, shorter-term droughts exhibit lower maximum duration and severity compared to longer-term events. In addition, maximum drought intensity tends to decrease as the SPI timescale increases. The spatial granularity offered by the ERA5-Land data significantly enhances the precision of drought characterization compared to traditional rain gauge networks, which are often unevenly distributed. Finally, a decrease in the 6- and the 12-month SPI values, meaning more severe droughts, has been identified in the north-western area. These insights underscore the importance of scale-dependent analysis in drought assessment, and support more informed water resource planning and climate adaptation strategies for vulnerable regions like Northern Algeria.