This study aims to investigate the shifts in rainfall patterns in the southwestern Mediterranean. It focuses on the upper Oum Er-Rbia basin in Morocco. Rainfall series from six stations, spanning over half a century (1970-2022), were analyzed at multiple temporal scales. Three key aspects of climate dynamics were targeted: variability using the coefficient of variation (CV), drought using the Standardized Precipitation Index (SPI), and trend based on the Mann-Kendall test, Sen's slope, and Innovative Trend Analysis (ITA). Results show a high rainfall variability, with an annual CV reaching 36 %. It exceeds 50 % at the seasonal scale. The SPI analysis highlights a structural drought, as 44 to 54 % of years are dry. Seasonal severe to extreme droughts are recurrent during spring and summer. Mann-Kendall and Sen's slope analysis indicates a general rainfall decrease, reaching-6.3 mm/yr. A significant reduction of winter and spring precipitation explains this trend. The ITA confirms this overall tendency. It further reveals a decline in low annual precipitation and an intensification in high values. These findings point to a shift toward more irregular and less predictable rainfall regimes, characterized by increased variability and concentration of precipitation. Such changes have critical implications for water resource management, particularly in terms of groundwater recharge, dam inflows, and long-term system resilience in semi-arid environments.