Inadvertent Tropical Rainfall Responses to Stratospheric Aerosol Injection: Disentangling Aerosol-Radiation-Precipitation Coupling in Convection-Resolving and Global Simulations

While the cooling from stratospheric aerosol injection (SAI) can offset greenhouse gas impacts on rainfall, direct radiative effects on the underlying troposphere can cause unintended rainfall changes. Here we use simulations of tropical climate with prescribed sea-surface temperatures to reveal how stratospheric aerosols directly heat the troposphere and subsequently modify convection, clouds, and precipitation. Our multi-model framework includes convection-resolving small-domain and mock-Walker simulations, alongside global climate model experiments. Across models, SAI produces a reduction in tropical mean rainfall, although this response is moderated – and made less predictable – by a reduction in cloud radiative heating. Regional rainfall anomalies within the tropics can be substantial, even though tropical circulation is found to be insensitive to aerosol direct radiative effects. These results clarify the mechanisms through which SAI can inadvertently alter hydroclimate, while highlighting key uncertainties for SAI risks stemming from poorly constrained cloud processes.