Summary
The study evaluates how climate warming and stratospheric aerosol injection (SAI) affect the South American Monsoon (SAM). CMIP6 models project later monsoon onset, minimal changes in demise, and a shorter rainy season – especially under high‑emission scenarios -alongside weakened rainfall intensity in Amazonia. In contrast, the SAI scenario (G6sulfur) preserves historical monsoon timing and duration but does not restore rainfall intensity, which remains similar to high‑warming outcomes. This highlights SAI’s partial effectiveness and significant hydrological risks for South America
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.
