South America Monsoon Lifecycle under SAI and no-SAI scenarios in a warming world

Abstract We validate the South American Monsoon (SAM) lifecycle (onset, demise, and length) and its intensity from a CMIP6 multi-model ensemble against observations (1995–2015), then assess changes across future periods under warming scenarios (SSP2-4.5, SSP3-7.0, SSP5-8.5) and a stratospheric aerosol injection (SAI) case (G6sulfur-experiment). The ensemble reproduces the rainfall spatial pattern and the observed NW–SE gradient in SAM onset. Projections indicate a robust onset delay by late century (∼2 pentads in SSP3-7.0; ∼3 in SSP5-8.5), while demise shifts are modest, resulting in a shortened rainy season from Amazonia through Brazil’s Midwest to the Southeast. These signals are robust across two different metrics, one of which is the inter-model agreement ⩾80%. In contrast, G6sulfur largely preserves historical timing, with little or no onset delay and a duration closer to the reference period and SSP2-4.5. However, SAM intensity is not restored to the reference period or to the SSP2-4.5 scenario. This study provides a first assessment of SAI effects on both the SAM lifecycle and intensity under global warming, contributing to the limited literature on the SAM lifecycle over South America.