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

==== Atlas.7.2.2 Assessment andSynthesis of Observations, Trends and Attribution ====

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Studies on climatic trends in South America indicate that mean temperature and extremely warm maximum and minimum temperatures have shown an increasing trend ( ''high confidence'' ), particularly for a large region in Northern South America and the south-western Andes (NSA, SAM, NES, SWS and the north of SES; [[#Skansi--2013|Skansi et al., 2013]] ; [[#de%20Barros%20Soares--2017|de Barros Soares et al., 2017]] ). Also, the trend of the difference between the annual mean of the daily maximum temperature and the annual mean of the daily minimum temperature was positive – up to 1°C per decade – over the extratropics with the maximum temperature generally increasing faster than the minimum temperature, while a negative trend of up to –0.5°C per decade was observed over the tropics.

Regionally, analyses of temperatures point to an increased warming trend ( ''high confidence'' ) over Amazonia over the last 40 years, which reached approximately 0.6°C–0.7°C (Figure Atlas.11 and the Interactive Atlas) and with stronger warming during the dry season and over the south-east. The analyses also showed that 2016 was the warmest year since at least 1950 ( [[#Marengo--2018b|Marengo et al., 2018b]] ). Andean temperatures showed significant warming trends, especially at inland and higher-elevation sites, while trends are non-significant or negative at coastal sites ( ''high confidence'' ) ( [[#Vuille--2015|Vuille et al., 2015]] ; [[#Burger--2018|Burger et al., 2018]] ; [[#Vicente-Serrano--2018|Vicente-Serrano et al., 2018]] ; [[#Pabón-Caicedo--2020|Pabón-Caicedo et al., 2020]] ). Over central Chile, positive trends are largely restricted to austral spring, summer and autumn seasons for mean, maximum and minimum temperatures ( [[#Burger--2018|Burger et al., 2018]] ; [[#Vicente-Serrano--2018|Vicente-Serrano et al., 2018]] ). Over Peru, trends of maximum air temperature were mainly amplified during the austral summer, but trends of cold-season minimum air temperature showed an opposite pattern, with the strongest warming being recorded in the austral winter ( [[#Vicente-Serrano--2018|Vicente-Serrano et al., 2018]] ).

In general, the spatial patterns of observed trends in temperature are more consistent than for precipitation across the whole of South America ( ''medium confidence'' ) (Interactive Atlas; [[#de%20Barros%20Soares--2017|de Barros Soares et al., 2017]] ). In south-east Brazil there is a region of highly significant decrease of rainfall in both wet and dry seasons recorded in the period 1979–2011 (Interactive Atlas; [[#Rao--2016|Rao et al., 2016]] ). The most consistent evidence of positive rainfall trend occurs in the southern part of the La Plata basin ( ''high confidence'' ) (southern Brazil, Uruguay, and north-eastern Argentina; [[#de%20Barros%20Soares--2017|de Barros Soares et al., 2017]] ). By contrast, there is ''high confidence'' that annual rainfall has decreased over north-east Brazil during the last decades ( [[#Carvalho--2020|Carvalho et al., 2020]] ). Contrary to temperature changes, trends in annual precipitation exhibit different signs across sectors in the Andes. For instance, annual precipitation trends in the north tropical (north of 8°S) and south tropical (8°S–27°S) Andes do not show a homogeneous pattern. Over the subtropical Andes, central Chile shows a robust signal of declining precipitation since 1970 ( ''high confidence'' ) ( [[#Pabón-Caicedo--2020|Pabón-Caicedo et al., 2020]] ).

Observational studies show that the dry-season length over southern Amazonia has increased significantly since 1979 ( ''high confidence'' ) ( [[#Fu--2013|Fu et al., 2013]] ; [[#Alves--2016|Alves, 2016]] ). In the Peruvian Amazon-Andes basin, there is no trend in mean rainfall during the period 1965–2007 ( [[#Lavado%20Casimiro--2012|Lavado Casimiro et al., 2012]] ) though statistically significant decreases in total annual rainfall in the central and southern Peruvian Andes from 1966 to 2010 were found ( [[#Heidinger--2018|Heidinger et al., 2018]] ). Despite that, recent analyses of Amazon hydrological and precipitation data suggest an intensification of the hydrological cycle over the past few decades ( [[#Gloor--2015|Gloor et al., 2015]] ). In general, these changes are attributed mainly to decadal climate fluctuations ( ''high confidence'' ), ENSO, the Atlantic SST north–south gradient, feedbacks between fire and land-use change mainly across southern south-eastern Amazon, and changes in the frequency of organized deep convection ( [[#Fernandes--2015|Fernandes et al., 2015]] ; [[#Sánchez--2015|Sánchez et al., 2015]] ; [[#Tan--2015|Tan et al., 2015]] ).

Since AR5, there has been limited attribution literature in the South America. Recent publications based on observational and modelling evidence assessed that anthropogenic forcing in CMIP5 models explains the overall warming ( ''high confidence'' ) over the entire South American continent, including the increase in the frequency of extreme temperature events ( [[#Hannart--2015|Hannart et al., 2015]] ). It has a detectable influence in explaining positive and negative precipitation trends observed in regions such as SES and the southern Andes ( [[#Vera--2015|Vera and Díaz, 2015]] ; [[#de%20Barros%20Soares--2017|de Barros Soares et al., 2017]] ; [[#Boisier--2018|Boisier et al., 2018]] ; [[#de%20Abreu--2019|de Abreu et al., 2019]] ). Despite that, there is ''limited evidence'' that human-induced greenhouse gas emissions had an influence on the 2014/2015 water shortage in south-east Brazil ( [[#Otto--2015|Otto et al., 2015]] ). Extreme event attribution on sub-continental scales is assessed in [[IPCC:Wg1:Chapter:Chapter-11|Chapter 11]] and continental-scale attribution in Chapter 3.

In summary, analyses of historical temperature time series point strongly to an increased warming trend ( ''high confidence'' ) across many South American regions, except for a cooling off the Chilean coast. Annual rainfall has increased over South-Eastern South America and decreased in most tropical land regions, particularly in central Chile ( ''high confidence'' ). The number and strength of extreme events, such as extreme temperatures, droughts and floods, have already increased ( ''medium confidence'' ) (Table 11.7).

It is noted that the major barrier to the study of climate change in many regions of South America is still the absence or insufficiency of long time series of observational data ( [[#Carvalho--2020|Carvalho, 2020]] ; [[#Condom--2020|Condom et al., 2020]] ). Most national datasets were created in the 1970s and 1980s, preventing a more comprehensive long-term trend analysis. To fulfil the users’ demand for climatological and meteorological data products covering the whole region, several interpolation techniques have been used with reanalysis and gridded gauge-analysis products to add the necessary spatial detail to the climate analyses over land and for climate variability and trend studies, but these are subject to uncertainties ( [[#Skansi--2013|Skansi et al., 2013]] ; [[#Rozante--2020|Rozante et al., 2020]] ).

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