Austral summer precipitation increased by 27% over the past 120 years in southeastern South America (SESA), a region including southern Brazil, Paraguay, Uruguay, and northern Argentina. This trend has driven widespread increases in agricultural production, making it important to understand if the trend will continue or reverse over the coming decades. A new paper led by Arianna Varuolo-Clarke, a 4th-year Ph.D. student in the Smerdon Climate Lab, investigates the influence of the South American low-level jet on SESA precipitation. Ari finds that a trend in this jet accounts for some of the observed rainfall increase in SESA from 1951 to 2020. Most of the jet trend comes from increased atmospheric moisture content, likely due to a combined impact of natural variations in the climate system and increased sea surface temperatures driven by human-caused global warming – a warmer ocean surface enhances evaporation, increasing humidity globally. Her results are important for understanding what is causing the rainfall trend, whether it will continue, and how we interpret climate models, which do not reproduce the observed rainfall trends in SESA over the last century or more.
TLDR? Check out Ari's Twitter thread on the paper. You can also get the long version by reading the open access paper here.