Inter-tropical African precipitation regime shifts dominated by tropical easterly jet

Abstract

Since the 1990s, inter-tropical Africa (ITA) has experienced consecutive calamitous droughts during the boreal spring. Although the observed precipitation regime changes have been attributed to tropical Indian Ocean-western Pacific warming and/or tropical Pacific La Niña-like cooling, the model-projected past-to-future widespread wetting response to anthropogenic warming overshadows qualitative attributions of decadal shifts in historical precipitation regimes and the reliability of near-term projections. The causes of ITA precipitation regime shifts and the likelihood of their future continuation remain unclear. Here, we reveal that the observed monopolar precipitation changes in ITA are primarily driven by the tropical easterly jet (TEJ)-dominated pattern, with a secondary contribution from the intertropical convergence zone (ITCZ)-mediated pattern. The Indo-Pacific warming-induced TEJ strengthening favors a monopolar drying trend from 1950 to 2022, while the northward-shifted ITCZ drives a west drying-east wetting dipolar pattern. Considering an observational TEJ constraint, an accelerated TEJ with an amplitude of -2 standard deviations could cause an almost threefold increase in extreme drying trends in the near term (2026–2045). Instead, ITA could face a higher likelihood of extreme wetting tendency due to a near-term TEJ weakening. Our findings underscore the importance of realistic TEJ simulations in enhancing confidence in future precipitation projections across hydroclimate-vulnerable Africa