Meteorological and Hydrological Drought Variability and Trends in the Oued Rdat Basin, Morocco: An Integrated SPI–SSFI and Trend Analysis Approach

Drought is a major hydroclimatic hazard in Mediterranean environments, affecting water availability and agricultural systems. This study investigates meteorological and hydrological drought variability and trends in the Oued Rdat Basin, Morocco, over 1970–2022. Meteorological and hydrological droughts were characterized using the Standardized Precipitation Index (SPI) and Standardized Streamflow Index (SSFI), respectively. Trends were assessed using the non-parametric Mann–Kendall and Spearman’s Rho tests, while Innovative Trend Analysis (ITA) was used to examine changes across different portions of the index distributions. The results reveal pronounced interannual variability, with recurrent alternation between dry and wet years and differences in hydrological variability between the upper and lower parts of the basin. Although positive and negative Sen’s slope estimates were observed for some SPI and SSFI series, all Mann–Kendall p-values exceeded 0.05, indicating that none of the detected monotonic trends were statistically significant at the 5% level. ITA nevertheless indicated distribution-dependent tendencies across different portions of the index distributions that were not identified by the conventional monotonic trend tests. Overall, drought variability was characterized by substantial interannual and distributional variability rather than a statistically significant long-term monotonic trend. The integrated SPI–SSFI framework provides useful information for drought assessment and water-resource management in the basin.