Editing IPCC:AR6/WGI/Chapter-8 (section)

===== 8.4.2.4.5 South American Monsoon =====

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The AR5 reported ''medium confidence'' that the South American monsoon (SAmerM) overall precipitation will remain unchanged, and ''medium confidence'' in projections of extreme precipitation. The AR5 also stated ''high confidence'' in the spatial expansion of the SAmerM, resulting from increased temperature and humidity.

Since AR5, some studies indicate that the SAmerM would experience changes in its seasonal cycle, with delayed monsoon onsets under increasing GHG emissions associated to different RCPs (Fu et al. , 2013; Reboita et al. , 2014; Boisier et al. , 2015; Pascale et al. , 2016; Seth et al. , 2019; [[#Sena--2020|Sena and Magnusdottir, 2020]] ) . In contrast, other studies indicate projected earlier onsets and delayed retreats of the SAmerM under the RCP8.5 scenario based on six CMIP5 models ( [[#Jones--2013|Jones and Carvalho, 2013]] ). These differences have been linked to the methodology used to determine monsoon timing, and sensitivity to the monsoon domain considered ( [[#8.3.2.4.5|Section 8.3.2.4.5]] ; [[#Correa--2021|Correa et al., 2021]] ). Recent studies provide further evidence for the projection of delayed SAmerM onsets by the late 21st century ( [[#Sena--2020|Sena and Magnusdottir, 2020]] ). An analysis of six CMIP6 models under the SSP5-8.5 scenario confirm the projections of delayed SAmerM onsets by the end of the 21st century ( [[#Moon--2020|Moon and Ha, 2020]] ). In addition, projected changes in the intensity and length of the SAmerM season have been found to be model-dependent ( [[#Pascale--2019|Pascale et al., 2019]] ). The analysis of CMIP5 projections of total monsoon rainfall indicate mixed signals in the Amazon and SAmerM regions ( [[#Jones--2013|Jones and Carvalho, 2013]] ; [[#Marengo--2014|Marengo et al., 2014]] ), with some studies suggesting increased summer precipitation in the core SAmerM region ( [[#Kitoh--2013|Kitoh et al., 2013]] ; [[#Seth--2013|Seth et al., 2013]] ). Dynamical downscaling of CMIP5 projections under the RCP4.5 and RCP8.5 scenarios with the Eta RCM suggests reductions of austral summer precipitation over the SAmerM region throughout the 21st century ( [[#Chou--2014|Chou et al., 2014]] ). Further analysis using 15 different CMIP6 models for the SSP2-4.5 scenario suggest reductions in total SAmerM rainfall ( [[#Wang--2020|]] [[#Wang--2020|]] [[#Wang--2020|]] [[#Wang--2020|B. Wang et al., 2020]] ). However, other analyses of CMIP6 projections under different SSP scenarios do not report clear changes in the SAmerM precipitation throughout the 21st century (Figure 8.22; Z. [[#Chen--2020|]] [[#Chen--2020|Chen et al., 2020]] b; [[#Jin--2020|Jin et al., 2020]] ). Similar uncertainties for all the SSP scenarios used across the report are found for other water cycle variables, including runoff and P–E (Table 8.2). Furthermore, there is disagreement in projected extreme precipitation in the region, with some CMIP5-based studies suggest reductions ( [[#Marengo--2014|Marengo et al., 2014]] ), while others indicate increases based on CMIP5 and CMIP6 models ( [[#Kitoh--2013|Kitoh et al., 2013]] ; [[#Sena--2020|Sena and Magnusdottir, 2020]] ).

In summary, there is ''high confidence'' that the SAmerM will experience delayed onsets in association with increases in GHG. However, there is ''low agreement'' on the projected changes in terms of total precipitation of the South American summer monsoon season.

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