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

===== Atlas.7.2.1.1 Key Features of the Regional Climate =====

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Regional synthesis of observed and modelled climate in South America is challenging due to the latitudinal extent of the continent, the Andes Mountains, and local-to-regional climatic features, which are influenced by multiple drivers. The main large-scale drivers include many modes of natural variability (Annex IV.2): the inter-decadal modes, Atlantic Multi-decadal Variability (AMV) and Pacific Decadal Variability (PDV); the interannual-to-annual modes, El Niño–Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), the Southern Annular Mode (SAM) and the North Atlantic Oscillation (NAO); seasonal variability driven by the meridional migration of the Inter-tropical Convergence Zone (ITCZ) and the timing and intensity of the South American Monsoon System (SAmerM, [[IPCC:Wg1:Chapter:Chapter-8#8.3.2.4.5|Section 8.3.2.4.5]] ), the Madden–Julian Oscillation sub-seasonal mode of natural variability (MJO) and the behaviour at finer scales of the tropical easterly waves.

The regional assessment in this section emphasizes the seven new South American reference regions (Figure Atlas.22; [[#Iturbide--2020|Iturbide et al., 2020]] ) that have a largely consistent climate and response to climate change, and can be used for analysis and impact studies ( [[#Solman--2008|Solman et al., 2008]] ; [[#Neukom--2010|Neukom et al., 2010]] ; [[#Barros--2015|Barros et al., 2015]] ; [[#Nobre--2016|Nobre et al., 2016]] ). At the sub-regional scale, several phenomena drive climate variability. Brazil’s north-east (North-Eastern South America; NES) is the most densely populated dryland globally and recurrently affected by climatic extremes. The climate variability, particularly the precipitation, is marked by strong interannual variability related to ENSO, the ITCZ, and the North Tropical Atlantic Ocean SSTs ( [[#Marengo--2018a|Marengo et al., 2018a]] ). Northern (NSA) and North-Western South America (NWS) are part of the Amazonia region. Its most recognizable features are the high rainfall, high humidity and high temperatures that prevail in the region. Rainfall variability in these regions results from the interplay between regional atmospheric circulation, the SST variations in both the Pacific and Atlantic oceans, among other regional-to-local interactions ( [[#Marengo--2016|Marengo and Espinoza, 2016]] ; [[#Espinoza--2020|Espinoza et al., 2020]] ). The South American Monsoon (SAM) region has distinct wet (summer) and dry (winter) periods. Key drivers include the South Atlantic Convergence Zone ( [[#Marengo--2012|Marengo et al., 2012]] ), the Bolivian High, the 40- to 60-day intra-seasonal oscillation, and the forcing of the high Andes Mountains to the west ( [[#Almeida--2017|Almeida et al., 2017]] ). The geographic position of South-Western South America (SWS) results in very specific climatic characteristics since SWS contains subtropical climates as well as sub-Antarctic and Antarctic climates. The climate of SWS is driven by seasonal changes in the position of subtropical high-pressure air masses in the South Atlantic and South Pacific oceans, the Southern Annular Mode, the dynamics of the cold Humboldt ocean current, and icy cold fronts and mid-latitude westerlies ( [[#Valdés-Pineda--2016|Valdés-Pineda et al., 2016]] ). The densely populated, highly productive sub-region of South-Eastern South America (SES) has cool winters and hot summers typical of the temperate zone, and climatic conditions are strongly tied to ENSO, whose influence is moderated by local air-sea thermodynamics in the South Atlantic ( [[#Barreiro--2010|Barreiro, 2010]] ). Lastly, the climate of the southern tip of South America (SSA) is cold and dry, and is influenced by the Southern Annular Mode, and the interaction between the wetter Pacific winds and the Andean Cordillera ( [[#Aceituno--1988|Aceituno, 1988]] ; [[#Silvestri--2009|Silvestri and Vera, 2009]] ).

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