Paleoclimate records have long documented the existence of multicentury hydroclimate anomalies in the Altiplano of South America. However, the causes and mechanisms of these extended events are still unknown. Here, we present a climate modeling experiment that explores the oceanic drivers and atmospheric mechanisms conducive to long-term precipitation variability in the southern Altiplano (18–25° S; 70–65 W; >3500 masl). We performed a series of 100-year-long idealized simulations using the Weather Research and Forecasting (WRF) model, configured to repeat annually the oceanic and atmospheric forcing leading to the exceptionally humid austral summers of 1983/1984 and 2011/2012. The aim of these cyclical experiments was to evaluate if these specific conditions can sustain a century-long pluvial event in the Altiplano. Unlike the annual forcing, long-term negative precipitation trends are observed in the simulations, suggesting that the drivers of 1983/1984 and 2011/2012 wet summers are unable to generate a century-scale pluvial event. Our results show that an intensification of the anticyclonic circulation along with cold surface air anomalies in the southwestern Atlantic progressively reinforce the lower and upper troposphere features that prevent moisture transport towards the Altiplano. Prolonged drying is also observed under persistent La Niña conditions, which contradicts the well-known relationship between precipitation and ENSO at interannual timescales. Contrasting the hydroclimate responses between the Altiplano and the tropical Andes result from a sustained northward migration of the Atlantic trade winds, providing a useful analog for explaining the divergences in the Holocene records. This experiment suggests that the drivers of century-scale hydroclimate events in the Altiplano were more diverse than previously thought and shows how climate modeling can be used to test paleoclimate hypotheses, emphasizing the necessity of combining proxy data and numerical models to improve our understanding of past climates.

In this study, we analyze the projected changes in mean and extreme precipitation and temperature over subtropical Chile, based on simulations of 3 Regional Climate Models (RCMs) (RegCM4-7, REMO2015, and ETA) from South-America CORDEX-CORE, each one driven by three different CMIP5 GCMs. The RCM’s performance for the present climate is evaluated against the CR2MET (~5km) dataset.The changes for the end (2070-2099) of the century for the RCP8.5 scenario are assessed with respect to the historical period (1976-2005). Extreme events are expressed in terms of 30-yrs return values, estimated from the GEV distribution fitted to seasonal extremes for extended austral winter and summer.Accordingly, to GCMs projections, robust mean drying conditions are found among RCMs between 35ºS-40ºS in winter and 35ºS-45ºS in summer over the continental Chile and adjacent ocean. North of 30ºS REMO2015 and ETA show a statistically significant increase of mean winter precipitation over mountain regions. Another robust signal among the RCMs consists in an increase of extreme winter precipitation north of 35ºS over the mountain area. Increases in the maximum and minimum temperatures are significant over all domain for the 3 RCMs, but it is prominent to the north of 35°S (30°S) for REMO2015 and RegCM4-7 for winter (summer), especially over the mountain leeward, while ETA depicts the higher heating in the south of 30°S. The changes are mainly associated with a positive displacement of distribution (changes in location parameter) for temperatures and the amplification of interannual variability (positive changes in scale parameter) for precipitation. The physical processes responsible for these changes are discussed.

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.