Editing IPCC:AR6/WGII/Chapter-12 (section)

==== 12.3.4.4 Impacts ====

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The Amazon and the Cerrado are among the largest and unique phytogeographical domains in SA. The Brazilian Cerrado is one of the most diverse savannah in the world, with more than 12,600 plant species, with 35% being endemic ( ''high confidence'' ) ( [[#Forzza--2012|Forzza et al., 2012]] ). Historic land cover change and concurrent climate change in the region strongly impacted the biodiversity and led to the extinction of 657 plant species for the Cerrado, which is more than four times the global recorded plant extinctions ( ''high confidence'' ) ( [[#Strassburg--2017|Strassburg et al., 2017]] ; [[#Green--2019|Green et al., 2019]] ). The effects of climate change, expressed by drought and heatwaves, lead to plant stress, compromising growth and increasing mortality ( [[#Yu--2019|Yu et al., 2019]] ). The fauna dependent on dew water was strongly impacted by the 1.6°C temperature rise that occurred from 1961 to 2019 ( ''medium confidence: medium evidence, medium agreement'' ) ( [[#Hofmann--2021|Hofmann et al., 2021]] ). Modelling outcomes project impacts in forest ecosystems in the region, with persistent warming and significant moisture reduction ( [[#Anjos--2021|Anjos et al., 2021]] ), leading to a potential change in the ecosystem structure and distribution in the region ( ''medium confidence: medium evidence, medium agreement'' ) ( [[#Government%20of%20Brazil--2020|Government of Brazil, 2020]] ).

The observed impact on plant species in SAM is projected to worsen in a warmer world ( [[#Warszawski--2013|Warszawski et al., 2013]] ). An increasing dominance of drought-affiliated genera of tree species has been reported in the southern part of the Amazon rainforest in the last 30 years ( ''medium confidence: medium evidence, medium agreement'' ) ( [[#Esquivel-Muelbert--2019|Esquivel-Muelbert et al., 2019]] ). Due to the tight relationship between drought and fire occurrence, an increase of 39% to 95% of burned area is modelled to impact the Cerrado region under RCP4.5 and RCP8.5, while under RCP2.6, a 22% overshoot in temperature is estimated to impact the area in 2050 decreasing to 11% overshoot by 2100 ( [[#Silva--2019d|Silva et al., 2019d]] ), leading to a high impact on agricultural production ( ''high confidence'' ).

SAM hosts the headwaters of important South American rivers, such as the Paraguay, Madeira, Tocantins-Araguaia and Xingu. The impact from climate change is expressed differently in several sub-regions. Extreme floods in the southern Amazon and Bolivian Amazon floodplains were described and related to the exceptionally warm sub-tropical South Atlantic ocean ( ''high confidence'' ) ( [[#Espinoza--2014|Espinoza et al., 2014]] ), causing high economic impacts (losses in crop and livestock production and infrastructure) and number of fatalities ( ''very high confidence)'' ( [[#Ovando--2016|Ovando et al., 2016]] ) ''.'' In contrast, declines in stream flow, particularly in the dry season, expressed by the ratio of runoff to rainfall, are observed for the southern part of the Amazon basin ( ''high evidence'' ) ( [[#Molina-Carpio--2017|Molina-Carpio et al., 2017]] ; [[#Espinoza--2019b|Espinoza et al., 2019b]] ; [[#Heerspink--2020|Heerspink et al., 2020]] ). Observed precipitation reduction in the Cerrado region impacted main water supply reservoirs for important cities in the Brazilian central region, leading to a water crisis in 2016/2017 ( [[#Government%20of%20Brazil--2020|Government of Brazil, 2020]] ) and affecting hydropower energy generation ( [[#Ribeiro%20Neto--2016|Ribeiro Neto et al., 2016]] ). Modelling studies project decreases in the river discharge rate on the order of 27% for the Tapajós basin and 53% for the Tocantins-Araguaia basin for the end of the century, which may affect freshwater biodiversity, navigation and generation of hydroelectric power ( ''medium confidence: medium evidence, high agreement'' ) ( [[#Marcovitch--2010|Marcovitch et al., 2010]] ; [[#Mohor--2015|Mohor et al., 2015]] ). This region also holds one of the largest floodplains in the world, the Pantanal. The climatic connection of Pantanal regions to the Amazon, and the influence of deforestation in local precipitation ( [[#Marengo--2018|Marengo et al., 2018]] ) has implications for conservation of ecosystem services and water security in Pantanal ( ''high confidence'' ) ( [[#Bergier--2018|Bergier et al., 2018]] ). Impacts of extreme drought, with increasing numbers of dry days and the peak of fire foci, were recently reported ( ''robust evidence'' ) ( [[#Lázaro--2020|Lázaro et al., 2020]] ; [[#Garcia--2021|Garcia et al., 2021]] ). The projected impacts of climate change will lead to profound changes in the annual flood dynamics for Pantanal wetlands, altering ecosystem functioning and severely affecting biodiversity ( ''high confidence'' ) ( [[#Thielen--2020|Thielen et al., 2020]] ; [[#Marengo--2021|Marengo et al., 2021]] ).

Soybean and corn yields in the Cerrado region will suffer one of the strongest negative impacts under the estimates of the RCP4.5 and RCP8.5 scenarios and will require high levels of investment in adaptation should they continue to be cultivated in the same areas as currently ( ''high confidence'' ) ( [[#Oliveira--2013|Oliveira et al., 2013]] ; [[#Camilo--2018|Camilo et al., 2018]] ). Changes in precipitation patterns are related to reductions in agricultural productivity and revenues in the southern portion of the Amazon region ( ''medium confidence: medium evidence, high agreement'' ) ( [[#Costa--2019|Costa et al., 2019]] ; [[#Leite-Filho--2021|Leite-Filho et al., 2021]] ). Thus, the future socioeconomic vigour of the region will be, to a large extent, connected to an unlikely stability of the regional climate and eventual fluctuations of global markets potentially affecting the agricultural supply chain ( ''high confidence'' ) ( [[#Nepstad--2014|Nepstad et al., 2014]] ).

Observations from recent past droughts in SAM indicate how the incidence of respiratory diseases may worsen under a drier and warmer climate. Northwest SAM had an approximately 54% increase in the incidence of respiratory diseases associated with forest fires during the 2005 drought compared to a no-drought 10-year mean ( ''high confidence'' ) ( [[#Ignotti--2010|Ignotti et al., 2010]] ; [[#Pereira--2011|Pereira et al., 2011]] ; [[#Smith--2014|Smith et al., 2014]] ). It is estimated that more than 10 million people are exposed to forest fires in the deforestation arc, a region comprising several Brazilian states in the southern and western parts of the Amazon rainforest, with several impacts on human health including potential exacerbation of the COVID-19 crisis in Amazonia ( ''medium confidence: medium evidence, high agreement'' ) ( [[#de%20Oliveira--2020|de Oliveira et al., 2020]] ) (Table 12.5). Increases in hospital admissions, asthma, DNA damage and lung cell death due to the inhalation of fine particulate matter represent an increase in public health system costs ( ''high confidence'' ) ( [[#Ignotti--2010|Ignotti et al., 2010]] ; Silva et al., 2013; [[#de%20Oliveira%20Alves--2017|de Oliveira Alves et al., 2017]] ; [[#Machin--2019|Machin et al., 2019]] ). The patchy landscape created by forest clearing contributes to a rising risk of zoonotic disease emergence by increasing interactions between wildlife, livestock and humans ( ''medium confidence: low evidence, medium agreement'' ) ( [[#Dobson--2020|Dobson et al., 2020]] ; [[#Tollefson--2020|Tollefson, 2020]] ). Recent studies also suggest an influence of climate change in zoonotic diseases, such as ''Orthohantavirus'' and ''Chapare'' viral infections, rodent-borne diseases, in some areas of Bolivia ( [[#Escalera-Antezana--2020a|Escalera-Antezana et al., 2020a]] ; [[#Escalera-Antezana--2020b|Escalera-Antezana et al., 2020b]] ). Extreme fluctuations in Amazon River levels were associated with a significant increase in the incidence of diarrhoea, leptospirosis and dermatitis ( [[#de%20Souza%20Hacon--2019|de Souza Hacon et al., 2019]] ; [[#Government%20of%20Brazil--2020|Government of Brazil, 2020]] ). According to a comprehensive characterisation of future heatwaves and alternative RCPs scenarios, Brazilian urban areas in the SAM region are projected to face increasing related mortality from 400% to 500% in the period 2031–2080 compared to the period 1971–2020, under the highest emission scenario and high-variant population scenario ( ''medium confidence: low evidence, medium agreement'' ) ( [[#Guo--2018|Guo et al., 2018]] ). Table 12.2 shows the increase in days of exposure to heatwaves already observed in the region.

The high risk of floods (high-frequency and costly damage) is centred in the Brazilian states of Acre, Rondônia, Southern Amazonas and Pará (Andrade et al., 2017). Global-scale studies indicate an increase of flood risk for the SAM region during the 21st century (consistent with floods that are more frequent) ( ''high confidence'' ) ( [[#Hirabayashi--2013|Hirabayashi et al., 2013]] ; [[#Arnell--2016|Arnell et al., 2016]] ; [[#Alfieri--2017|Alfieri et al., 2017]] ). Higher emission scenarios result in substantially higher flood risks than low emission scenarios ( [[#Alfieri--2017|Alfieri et al., 2017]] ).

'''Table 12.2 |''' Average change in mean number of days exposed to heatwaves (defined as a period of at least 2 d where both the daily minimum and maximum temperatures are above the 95th percentile for their respective climatologies) in the over-65 population in 2016–2020 relative to 1986–2005. Temperature data taken from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 data set; calculations were derived from Romanello et al. (2021).

{| class="wikitable"
|-
! '''Country'''

! '''Number of additional days of heatwave exposure in 2016–2020 relative to 1986–2005'''

|-
| Argentina

| 4.9

|-
| Belize

| 8.8

|-
| Bolivia

| 2.2

|-
| Brazil

| 3.1

|-
| Chile

| 3.3

|-
| Colombia

| 9.3

|-
| Costa Rica

| 0.8

|-
| Ecuador

| 7.6

|-
| El Salvador

| 2.2

|-
| Guatemala

| 8.4

|-
| Guyana

| 8.2

|-
| Honduras

| 11.2

|-
| Nicaragua

| 2.2

|-
| Panama

| 2.6

|-
| Paraguay

| 2.6

|-
| Peru

| 3.6

|-
| Suriname

| 15.2

|-
| Uruguay

| 2.7

|-
| Venezuela

| 8.5

|}

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