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

==== 12.3.6.1 Hazards ====

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An increase in the intensity and frequency of hot extremes and decrease in the intensity and frequency of cold extremes were observed with ''high confidence'' ( [[#Rusticucci--2017|Rusticucci et al., 2017]] ; [[#Wu--2017|Wu and Polvani, 2017]] ) (WGI AR6 Table 11.13) ( [[#Seneviratne--2021|Seneviratne et al., 2021]] ). There is ''low confidence'' that the decrease in hot extremes over SES is related to an increase in extreme precipitation ( [[#Wu--2017|Wu and Polvani, 2017]] ).

Over SES most stations have registered an increase in annual rainfall, largely attributable to changes in the warm season; this is one of few sub-regions where a robust positive trend in precipitation and significant intensification of heavy precipitation have been detected since the early 20th century ( ''high confidence'' ) but with ''medium confidence'' in a reduction of hydrological droughts ( [[#Vera--2015|Vera and Díaz, 2015]] ; [[#Saurral--2017|Saurral et al., 2017]] ; [[#Lovino--2018|Lovino et al., 2018]] ; [[#Avila-Diaz--2020|Avila-Diaz et al., 2020]] ; [[#Carvalho--2020|Carvalho, 2020]] ; [[#Dereczynski--2020|Dereczynski et al., 2020]] ; [[#Dunn--2020|Dunn et al., 2020]] ; [[#Marengo--2020a|Marengo et al., 2020a]] ; [[#Olmo--2020|Olmo et al., 2020]] ) (WGI AR6 Table 11.14) ( [[#Seneviratne--2021|Seneviratne et al., 2021]] ). A higher observed frequency of extratropical cyclones in the region has been detected ( [[#Parise--2009|Parise et al., 2009]] ; [[#Reboita--2018|Reboita et al., 2018]] ) with three cyclogenetic foci: south-southeastern Brazil, extreme south of Brazil and Uruguay, and southeastern Argentina.

In Montevideo, mean sea levels have increased over the past 20 years, reaching 11 cm from 1902 to 2016, and a recent accelerating trend has been observed ( [[#Gutiérrez--2016b|Gutiérrez et al., 2016b]] ). A value of water level rise and its acceleration for Buenos Aires was calculated from a record of annual mean water levels obtained from hourly levels (1905–2003). Annual mean water level showed a trend of +1.7 ± 0.05 mm yr −1 and an acceleration of +0.019 ± 0.005 mm yr −2 ( [[#D’Onofrio--2008|D’Onofrio et al., 2008]] ).

Increasing trends in mean air temperature and extreme heat and decreasing cold spells are projected ( ''high confidence'' ) (WGI AR6 Table 12.6) ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). The increase in the frequency of warm nights is larger than that projected for warm days, consistent with observed past changes that have been related to changes in cloud cover that affect daytime temperatures differently than nighttime temperatures ( [[#López-Franca--2016|López-Franca et al., 2016]] ; [[#Menéndez--2016|Menéndez et al., 2016]] ; [[#Feron--2019|Feron et al., 2019]] ).

Increases in mean precipitation ( ''high confidence'' ), pluvial floods and river floods are projected ( ''medium confidence'' ) ( [[#Nunes--2018|Nunes et al., 2018]] ) (WGI AR6 Table 12.6) ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). Droughts in the River Plate basin will be more frequent in the medium term (2011–2040) and the distant future (2071–2100) (with respect to the 1979–2008 period), but also shorter and more severe, for the more extreme emission scenario (RCP8.5) ( ''low confidence'' ) ( [[#Carril--2016|Carril et al., 2016]] ) ''.''

Negative trends in the annual number of cyclone events in the long term of 3.6% to 6.5% (2070–2098) are projected and showed an increase of 3% to 11% (2080–2100 for the A1B scenario) ( [[#Grieger--2014|Grieger et al., 2014]] ; [[#Reboita--2018|Reboita et al., 2018]] ). All coastal and oceanic climate impact drivers (relative sea level, coastal flood and erosion, marine heatwaves and ocean aridity) are expected to increase by mid-century in the RCP8.5 scenario ( ''high confidence'' ) (WGI AR6 Table 12.6) ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ).

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