The global Sahel Monsoon Ocean-Pressure Index reconciles its regional and large-scale features

Monitoring Sahelian rainfall variability is increasingly critical as climate extremes intensify across the region. Here, we develop the Sahelian Monsoon Ocean-Pressure Index (SMOPI), a new global synthetic index constructed from five dynamically coherent sea-level pressure regions statistically linked to June-September Sahel monsoon rainfall (Tamoffo et al. 2025). SMOPI portrays intra-seasonal and interannual variability, and crucially, reflects the influence of both regional processes and large-scale teleconnections on monsoon dynamics. SMOPI aligns with the dominant rainfall variability mode both in reanalyses and 29 CMIP6 models. Strong/positive SMOPI phases coincide with wet years and are associated with enhanced convergence, favorable jet configurations, and robust Pacific, Atlantic, and Indian Ocean teleconnections. Conversely, weak/negative SMOPI phases correspond to drought conditions and divergent moisture fluxes. SMOPI exposes climate model failures in reproducing historical droughts and offers new physical insights into rainfall-driving mechanisms. It has a potential to be a scalable, transferable diagnostic tool for monitoring, forecasting, and evaluating Sahelian monsoon rainfall under global warming.

Tamoffo, A.T., Weber, T., Mouassom, F.L. et al. The global Sahel monsoon ocean-pressure index reconciles its regional and large-scale features. npj Clim Atmos Sci 8, 323 (2025). https://doi.org/10.1038/s41612-025-01226-2