Model uncertainty in synoptic circulation patterns and precipitation changes in Southern South America using CMIP5 and CMIP6 models

Abstract The effects of global warming on the regional climate of southern South America (SSA) during the recent decades have been exhaustively documented with consistency throughout the literature. However, the projected changes on temperature- and precipitation-related climate hazards depict an important uncertainty, mostly in the intensity of the changes. This work assessed a set of CMIP5 and CMIP6 global climate models (GCMs) in reproducing the observed atmospheric circulation patterns (CPs) over SSA and their expected changes for the 21st century. Furthermore, the attribution of the seasonal precipitation changes to changes in the CPs was explored for the late future (2070–2100). GCMs were generally able to represent the variety of CPs and their seasonal frequencies, although presenting more deficiencies in capturing their respective precipitation patterns over SSA. Larger model agreement was found in the increasing and/or decreasing frequency of specific CPs for the near future (2040–2070) than for the late future, when model spread became more noticeable. Particularly, CPs associated with larger positive rainfall anomalies over southeastern South America -a hotspot for precipitation extremes- are expected to become more frequent in the near future, whereas their changes in the longer-term are more uncertain. When performing an attributional study, precipitation changes showed important differences between GCMs and were often associated with changes in the intra-pattern variability rather than in the CPs changing frequency. In this way, the modification of the precipitation regime of SSA may not be explained only by changes in the large-scale circulation but probably also by other regional-to-local features.