Plausible Drying and Wetting Scenarios for Summer in Southeastern South America

MINDLIN, JULIA; VERA, CAROLINA S.; SHEPHERD, THEODORE G.; OSMAN, MARISOL

JOURNAL OF CLIMATE

AMER METEOROLOGICAL SOC

Año: 2023 vol. 36 p. 7973 - 7991

0894-8755

Summer rainfall trends in Southeastern South America (SE-SA) have received attentionin recent decades because of their importance for climate impacts. More than one drivingmechanism has been identified for the trends, some of which have opposing effects. It is still notclear how much each mechanism has contributed to the observed trends or how their combinedinfluence will affect future changes. Herewe address the second question and study howthe CMIP6summer SE-SArainfall response to greenhousewarming can be explained by mechanisms related tolarge-scale extratropical circulation responses in the Southern Hemisphere to remote drivers (RDs)of regional climate change. We find the regional uncertainty is well represented by combining theinfluence of four RDs: tropical upper tropospheric amplification of surface warming, the delay inthe stratospheric polar vortex breakdown date, and two RD’s characterizing recognized tropicalPacific SST warming patterns. Applying a storyline framework, we identify the combination ofRD responses that lead to the most extreme drying and wetting scenarios. Although most scenariosinvolve wetting, SE-SA drying can result if high upper-tropospheric tropical warming and earlystratospheric polar vortex breakdown conditions are combined with low central and eastern Pacificwarming. We also show how the definition of the SE-SA regional box can impact the results, sincethe spatial patterns characterizing the dynamical influences are complex and the rainfall changescan be averaged out if these are not considered when aggregating. This article’s perspective andthe associated methodology are applicable to other regions of the globe.