Recommended citation: Stojanovic, M., Sori, R., Pérez-Alarcón, A., Hassan, R. H., Ismail, F. R. A., Eldeen, R. E., Nieto, R., Gimeno, L. (2025). Multiscale drought episodes and long-term drying trends in Northwestern Africa during 1950–2022. MedGU Annual Meeting. Athens, Grece, 10-12 November 2025.

Abstract

​Northwestern Africa (NWA) is a region characterized by temperate Mediterranean and semi-arid hot climates, vulnerable to droughts, which significantly impact agriculture, ecosystems, and water resources. In this study, we investigated the occurrence and evolution of drought episodes during the period 1950–2022. ERA5-Land precipitation data with a resolution of 0.1º were used to calculate the Standardized Precipitation–Evapotranspiration Index (SPEI) at time scales from 1 to 24 months. A drought episode occurs when the SPEI falls below zero and reaches at least -0.84, ending in the last month before it becomes positive. The results reveal frequent short events at scales of one to six months, while multi-year droughts emerged at longer time scales. Particularly severe and persistent episodes include 1992–1995 (SPEI12, duration of 47 months, severity 36.6), 2015–2018 (SPEI-12 duration of 30 months; SPEI-24 duration of 34 months). The longest and most severe episode occurred between September 1998 and December 2002, lasting 52 months at SPEI- 12, with a cumulative severity of 69.88 and a peak intensity of 2−2.54. Trend analyses of the SPI12 indicate a persistent drying tendency across the northwestern sector of Morocco, northern Algeria, and northeastern Tunisia. The results also indicate that surface monthly evaporation is negatively coupled with SPI1 across the Maghreb and the Mediterranean coast in NWA, highlighting that lower precipitation and reduced water availability translate into simultaneous evaporation increase. This pattern reflects the strong control of soil water availability on land–atmosphere exchanges in semi-arid environments. In addition, negative correlations are observed in the western Mediterranean Sea, and a region of the Atlantic Ocean adjacent to NWA and the Iberian Peninsula. This confirms that both regions act as important oceanic moisture sources for precipitation over the NWA, modulating the occurrence of dry conditions. A complementary analysis of moisture transport through the vertically integrated moisture flux confirmed this statement. This study provides a comprehensive characterization of drought behaviors in NWA, underlining the consolidation of a long-term drying trend, and showing possible coupling with evaporation from adjacent oceanic regions. These findings contribute to improving drought monitoring and designing water and land management strategies.