Trajectories of Atmospheric Rivers in the Southern Hemisphere under CMIP6 and Solar Radiation Modification

Our study assesses the differences in intensity and frequency of Atmospheric Rivers (ARs) between Solar Radiation Modification (SRM) scenarios and greenhouse gas emission pathways. ARs are among the most important freshwater sources in the midlatitudes. This tropical humidity, transported horizontally to extratropical regions as plumes of water vapor, is associated with extreme precipitation at landfall, which usually triggers natural hazards, such as landslides and floods, especially in arid, semi-arid, and Mediterranean regions. While Earth System Models project more intense AR events and poleward displacement of landfall locations as warming deepens during the 21st century, driven by changes of atmospheric dynamics such as the position of the descending branch of the Hadley Cell, little is known about how SRM’s global warming mitigation goals may alter atmospheric circulation patterns and hence AR characteristics, especially in the Southern Hemisphere. We compare two SRM scenarios, G6Solar (reduction of the solar constant) and G6Sulfur (Stratospheric Aerosol Injection), and two CMIP6 model outputs under greenhouse gas emission pathways SSP2-4.5 and SSP5-8.5. Results reveal an overall decrease in AR frequency in extratropical regions by the end of the century. Conversely, the mid-latitudes experience increases in AR frequency. Under G6solar, frequency change is of similar magnitude as for the SSP2-4.5 scenario, whereas the G6sulfur scenario matches SSP5-8.5’s closest. Regarding ARs’ intensity, we detect worldwide increases in transported moisture content, irrespective of scenarios, with a small decrease near the west coast of South America. The role of SRM on projected changes in the dynamics and thermodynamics of the processes is discussed. These results signal that the Southern Hemisphere’s atmospheric dynamics are not neutral to the SRM technique, as they may deliver a significantly different AR scenario by the end of the century, even if the intended global cooling goals are met.