Thermodynamic intensification and atmosphere-soil coupling of drought in North-West Africa

Drought in North-West Africa (NWA) results from the combined influence of precipitation deficits and increasing atmospheric evaporative demand. This study analyses drought variability across Morocco, northern Algeria and Tunisia during 1981–2024 using the Standardised Precipitation Index (SPI3) and the Standardised Precipitation–Evapotranspiration Index (SPEI3). This study integrates drought indices, copula-based atmosphere–soil coupling, seasonal drought ranking, and event-synchronisation networks into a unified regional drought framework. The SPEI3 identifies a higher number of drought-affected months than SPI3 over most of the region, indicating that atmospheric evaporative demand enhances drought occurrence beyond precipitation deficits alone. The ranking analysis shows that several of the most severe and spatially extensive events were concentrated in the most recent years of the record following a reduced precipitation and increasing atmospheric evaporative demand. In addition, there is a strong coupling and dependence between SPI/SPEI drought and soil water content depletion, particularly over the semi-arid inland belt. The event-synchronisation analysis further show that drought occurrence is organised around a connected inland drought corridor, while Mediterranean, Atlantic-facing, and interior domains are more clearly differentiated in SPEI3 than in SPI3. Finally, seasonal trends indicate widespread drying from winter to summer, whereas autumn shows a more heterogeneous signal. Overall, the results demonstrate that drought intensification in NWA is increasingly controlled by the interaction between atmospheric warming, soil moisture depletion, and spatial drought connectivity.