Recent Trends in Extreme Precipitation and Temperature over Southeastern South America: The Dominant Role of Stratospheric Ozone Depletion

Observations show an increase in maximum precipitation extremes and a decrease in maximum temperature extremes over southeastern South America (SESA) in the second half of the 20th century. The Community Earth System Model (CESM) Large Ensemble (LE) experiments are able to successfully reproduce the observed trends of extreme precipitation and temperature over SESA. Careful analysis of a smaller ensemble of CESM-LE single forcing experiments reveals that the trends of extreme precipitation and temperature over SESA are mostly caused by stratospheric ozone depletion. The underlying dynamical mechanism is investigated, and it is found that, as a consequence of stratospheric ozone depletion and the resulting southward shift of tropospheric jet streams, anomalous easterly flow and more intense cyclones have occurred over SESA, which are favorable for heavier rainfall extremes and milder heat extremes.