Contrasting Changes in Rainfall Structure Between Monsoon and Adjacent Dry Regions Under Stratospheric Aerosol Injection

Abstract Rainfall structure is projected to shift toward heavier precipitation under global warming due to increased atmospheric moisture. Such a shift can heighten the risks of both floods and droughts. Stratospheric aerosol injection (SAI) has been proposed to counteract continued warming, but its effects on rainfall structure and potential to introduce new hydrological risks remain unclear. Here, using simulations from two models (CESM2 and UKESM1) participating in ARISE‐SAI‐1.5, we show that restoring global mean temperature increase to 1.5°C through SAI produces contrasting responses between monsoon and adjacent dry regions. Specifically, the global monsoon region is expected to experience a reduction in heavy rainfall, while the global dry region exhibits increased precipitation across a broad range of intensities. Inter‐model comparisons further reveal the sensitivity of rainfall structure to residual temperature anomalies over monsoon sub‐regions. Monsoon regions exhibit reduced heavy rainfall but increased drought risk in the hemisphere experiencing stronger cooling. In contrast, dry regions consistently experience enhanced precipitation and fewer dry days across models. These responses are primarily driven by dynamic processes rather than thermodynamic effects. The emergence of potential new regional “hotspots” of precipitation extremes underscores the need for caution when deploying SAI.