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

==== 12.4.4.2 Wet and Dry ====

<div id="h3-51-siblings" class="h3-siblings"></div>

'''Mean precipitation:''' The ( [[IPCC:Wg1:Chapter:Atlas|Atlas]] documents diverse historical precipitation trends in the region, including a small but not significant increasing trend in SCA, a decreasing trend in south-eastern and north-eastern Brazil, and an increasing trend in SSA. Projections indicate a drying signal for SCA ( ''medium confidence'' ) ( [[#Coppola--2014a|Coppola et al., 2014a]] ; [[#Nakaegawa--2014|Nakaegawa et al., 2014]] ), NES and SWS ( ''high confidence'' ) (Atlas.7.2.5) and the well-known dipole for South America, meaning increasing precipitation over subtropical regions like the Río de La Plata basin (SES) ( ''high confidence'' ) and decreasing precipitation in the Amazon (NSA) ( ''medium confidence'' ) ( [[#Chou--2014|Chou et al., 2014]] ; [[#Llopart--2014|Llopart et al., 2014]] ; [[#Reboita--2014|Reboita et al., 2014]] ; [[#Sánchez--2015|Sánchez et al., 2015]] ; [[#Teichmann--2021|Teichmann et al., 2021]] ). These features are consistent with observations ( [[#Sena--2018|Sena et al., 2018]] ) and are evident in regional and global model projections by mid- and end-of-century for both RCP4.5 and RCP8.5 ( [[#Jones--2013|Jones and Carvalho, 2013]] ).

'''River flood:''' Emerging literature in the region documents ongoing changes in river floods. [[#Mernild--2018|Mernild et al. (2018)]] report decreases and increases in annual runoff west of the Andes Cordillera’s continental divide, with the greatest decreases in the number of low (&lt;10th percentile) runoff conditions and the greatest increases in high (&gt;90th percentile) runoff conditions. In coastal north-east Peru, extreme precipitation events recently caused devastating river floods and landslides ( [[#Son--2020|Son et al., 2020]] ). In Brazil, floods are becoming more frequent and intense in wet regions but less frequent and intense in drier regions ( [[#Bartiko--2019|Bartiko et al., 2019]] ; [[#Borges%20de%20Amorim--2019|Borges de Amorim and Chaffe, 2019]] ), with higher propagation of hydrological changes through anthropogenically modified agricultural basins ( [[#Chagas--2018|Chagas and Chaffe, 2018]] ). Record, catastrophic, unprecedented, and once-in-a-century flooding events have also been reported in recent decades in the tributaries of the Amazon River or along its mainstream ( [[#Sena--2012|Sena et al., 2012]] ; [[#Espinoza--2013|Espinoza et al., 2013]] ; [[#Marengo--2013|Marengo et al., 2013]] ; [[#Filizola--2014|Filizola et al., 2014]] ), in Argentinean rural and urban areas ( [[#Barros--2015|Barros et al., 2015]] ), in the lower reaches of the Atrato, Cauca and Magdalena rivers in Colombia ( [[#Hoyos--2013|Hoyos et al., 2013]] ; [[#Ávila--2019|Ávila et al., 2019]] ), in basins whose mainstreams flow through important metropolitan areas such as Concepción, Chile ( [[#Rojas--2017|Rojas et al., 2017]] ), and even in one of Earth’s driest regions, the Atacama Desert ( [[#Wilcox--2016|Wilcox et al., 2016]] ). In the Amazon basin, the significant increase in extreme flow is associated with the strengthening of the Walker circulation ( [[#Barichivich--2018|Barichivich et al., 2018]] ).

Available projections for the region show increases in river floods in SES and SAM ( ''medium confidence'' ). Projections indicate that SES and the coasts of Ecuador and Peru will experience a tendency towards wetter conditions that can be a proxy for longer periods of flooding and enhanced river discharges ( [[#Zaninelli--2019|Zaninelli et al., 2019]] ). CORDEX models project the strongest changes for the peak flow with a return period of 100 years in SES by mid-century and under RCP8.5 (Figure 12.8). At the continental scale, on the contrary, [[#Alfieri--2017|Alfieri et al. (2017)]] suggest that 100-year river floods will decrease under RCP8.5. Regional projections of river floods have high uncertainty, however, owing to differences in hydrological models ( ''low confidence'' ) ( [[#Reyer--2017a|Reyer et al., 2017a]] ). [[#Fábrega--2013|Fábrega et al. (2013)]] projected increases in surface runoff for Panama, while [[#Zulkafli--2016|Zulkafli et al. (2016)]] identified increases in 100-year floods of 7.5 and 12.0% in projections for the Peruvian Amazon wet season under RCPs 4.5 and 8.5 respectively. Wetter conditions and ±20% variations in annual mean streamflow are also projected for the Río de La Plata under the warming levels of 1.5°C, 2°C and 3°C above pre‐industrial conditions ( [[#Montroull--2018|Montroull et al., 2018]] ). In central Chile, 50-year peak flows are expected to be greater by mid-century than 100-year peak flows observed over the reference period ( [[#Bozkurt--2018|Bozkurt et al., 2018]] ).

<div id="_idContainer065" class="Basic-Text-Frame"></div>

[[File:53a6b519979090f129d90509a8f91c08 IPCC_AR6_WGI_Figure_12_8.png]]

'''Figure 12.8''' '''|''' '''Projected changes in selected climatic impact-driver indices for Central and South America.'''

'''Heavy precipitation and pluvial flood:''' Table 11.14 indicated that there is ''low confidence'' due to ''limited evidence'' of extreme precipitation trends in almost all Central and South America, except in SES where increases in the magnitude and frequency of heavy precipitation have been observed ( ''high confidence'' ). In general, data scarcity persists for a representative continental assessment. [[IPCC:Wg1:Chapter:Chapter-11|Chapter 11]] projections indicate ''low confidence'' of increase, compared to the modern period, in the intensity and frequency of heavy precipitation in SCA and SWS for all GWLs, and ''medium confidence'' of increase in NSA, NES, SSA, SAM and SES for GWL of 4°C. In NWS, a wide range of changes is projected ( ''low confidence'' ).

'''Landslide:''' Several regions in Central America, as well as Colombia and south-eastern Brazil, are considered areas of high incidence of observed fatal landslides. In these areas, El Niño–Southern Oscillation (ENSO)-driven fluctuations in rainfall amounts ( [[#Sepúlveda--2015|Sepúlveda and Petley, 2015]] ) and climate change ( [[#Nehren--2019|Nehren et al., 2019]] ) seem to be key factors. Rockfalls, ice- and rock-ice avalanches, lahars and landslides have been reported frequently in the southern, extratropical Andes in the last decades ( [[#Gariano--2016|Gariano and Guzzetti, 2016]] ). A large number of ice- and moraine-dammed lakes have consequently failed, causing floods that rank amongst the largest events ever recorded ( [[#Iribarren%20Anacona--2015|Iribarren Anacona et al., 2015]] ). However, published literature is largely missing for a reliable assessment of past and future trends of such hazards.

'''Aridity:''' Several regional studies suggest increasing trends in the frequency and length of droughts in the region, such as: over NWS ( [[#Domínguez-Castro--2018|Domínguez-Castro et al., 2018]] ), NSA ( [[#Marengo--2016|Marengo and Espinoza, 2016]] ; [[#Cunha--2019|Cunha et al., 2019]] ) and NES ( [[#Marengo--2015|Marengo and Bernasconi, 2015]] ), over southern Amazonia ( [[#Fu--2013|Fu et al., 2013]] ; [[#Boisier--2015|Boisier et al., 2015]] ), in the São Francisco River basin and the capital city Distrito Federal in Brazil ( [[#Borges--2018|Borges et al., 2018]] ; [[#Bezerra--2019|Bezerra et al., 2019]] ), in the southern Andes ( [[#Vera--2015|Vera and Díaz, 2015]] ), in central southern Chile ( [[#Boisier--2018|Boisier et al., 2018]] ), in SES ( [[#Rivera--2014|Rivera and Penalba, 2014]] ) and, during recent years, in SSA ( [[#Rivera--2014|Rivera and Penalba, 2014]] ). [[IPCC:Wg1:Chapter:Chapter-8|Chapter 8]] indicated ''medium confidence'' of anthropogenic forcing on observed drying trends in central Chile. Additional discussion on droughts and aridity trends in South America is presented in Sections 8.3.1.6, 8.4.1.6 and 8.6.2.1.

Sections 8.3.2.4 and 8.4.1.6 point to two important drying hotspots in South America with long-term soil moisture decline and precipitation declines: the Amazon basin (SAM and NSA) and SWS ( ''medium confidence'' ) (Figure 12.4). End-of-century RCP8.5 projections show a longer dry season in the central part of South America and decreased precipitation over the Amazon and central Brazil ( [[#Teichmann--2013|Teichmann et al., 2013]] ; [[#Coppola--2014a|Coppola et al., 2014a]] ; [[#Giorgi--2014|Giorgi et al., 2014]] ; [[#Llopart--2014|Llopart et al., 2014]] ; Atlas.7). Seasonal changes are also projected by end century under RCP 8.5, with decreases in June–July–August (JJA) rainfall projected for NSA, the coastal region of SES, SAM and the southern portion of SWS ( [[#Marengo--2016|Marengo et al., 2016]] ). Decreases in December –January–February (DJF) rainfall are projected for the central part of South America in the near term ( [[#Kitoh--2011|Kitoh et al., 2011]] ; [[#Chou--2014|Chou et al., 2014]] ; [[#Cabré--2016|Cabré et al., 2016]] ). Regional projections for Central and South America also indicate an increase in dryness in SCA and NES by mid- to end-century ( ''medium confidence'' ) ( [[#Chou--2014|Chou et al., 2014]] ; [[#Marengo--2015|Marengo and Bernasconi, 2015]] ).

'''Hydrological drought:''' [[IPCC:Wg1:Chapter:Chapter-11|Chapter 11]] assessed mostly ''low confidence'' in observed changes in hydrological droughts given a lack of studies and clear evidence, with ''medium confidence'' only for a streamflow decrease in sub-regions of SWS (Table 11.15). Some trends are becoming more clear, such as the ones reported for Colombia (NWS) by [[#Carmona--2014|Carmona and Poveda (2014)]] , who indicated that 62% of the 25- to 50-year-long monthly average streamflow time series exhibited significant decreasing trends. However, studies of discharge changes indicate that uncertainty is still large, as argued by [[#Pabón-Caicedo--2020|Pabón-Caicedo et al. (2020)]] for the full extent of the Andes.

A number of studies project decreases in runoff and river discharge for SCA, Colombia, Brazil and the southern part of South America by the end of this century ( [[#Nakaegawa--2010|Nakaegawa and Vergara, 2010]] ; [[#Arnell--2013|Arnell and Gosling, 2013]] ; [[#van%20Vliet--2013|van Vliet et al., 2013]] ). [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] assessed ''high confidence'' in projections of increases in hydrological droughts in NSA, SAM, SWS, and SSA under for 4°C GWL, ''medium confidence'' in SCA, and ''low confidence'' in the rest of the sub-regions given insufficient evidence, lack of signal or mixed signals among the available studies. Signals are much more uncertain for the middle of the century (or for a 2°C GWL).

'''Agricultural and ecological drought:''' Section 11.9 assessed ''low confidence'' in observed changes in agricultural and ecological drought across Central and South America due to regional heterogeneity and differences depending on the drought metrics used, except in NES, which has seen a dominant increase in drought severity ( ''medium confidence'' ).

NSA and SAM are the two regions where the strongest signal of increasing number of dry days (NDD) and drought frequency (DF) is projected compared to other regions of the world ( [[#Coppola--2021b|Coppola et al., 2021b]] ). By the end of this century and under RCP8.5, the NSA area average value for NDD reaches 43, 32 and 27, within the CORDEX-CORE, CMIP5 and CMIP6 ensembles respectively. For the frequency of droughts, the NSA area average value is of about 4.6, 3.4 and 3.8. For the same period and scenario, the SAM region shows NDD and DF values of 29, 20 and 21, and of 4, 3 and 3.5 respectively (Figure 12.4j–l). In Central America, a significantly drier northern region and a wetter southern region are projected for mid-century by ( [[#Hidalgo--2017|Hidalgo et al., 2017]] ), whilst [[#Fuentes-Franco--2015|Fuentes-Franco et al. (2015)]] pointed to more pronounced dry periods during the rainy season in SCA by the end of this century under RCP8.5. Increases in the frequency of meteorological droughts that may initiate other drought types are projected for the eastern part of the Amazon and the opposite for the west under RCP8.5 ( [[#Duffy--2015|Duffy et al., 2015]] ). In central Chile, the occurrence of extended droughts, such as the recently experienced 2010–2015 megadrought (which is still driving impacts), is projected to increase from one to up to five events per 100 years under RCP8.5 ( [[#Bozkurt--2018|Bozkurt et al., 2018]] ). [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] highlights change in confidence in increases in drought severity in SCA, NSA, NES, SAM, SWS, and SSA from ''low'' to ''high'' under the three GWLs of 1.5°C, 2°C and 4°C. NES and SES change from ''low'' ''confidence'' to ''medium'' ''confidence'' increases in agricultural and ecological drought severity by 4°C GWL with different metrics and ''high agreement'' between studies. Only SAM and SSA have projections of agricultural and ecological drought increasing with ''high confidence'' for the middle of the century, or for a 2°C GWL, and NSA, NES and SCA are projected to increase with ''medium confidence'' .

'''Fire weather:''' There is evidence of increases in forest fire activity (number of fires, burned area and fire duration) in central and south-central Chile, where more conducive fire weather conditions have been proposed as the main driver ( [[#González--2018|González et al., 2018]] ; [[#Urrutia-Jalabert--2018|Urrutia-Jalabert et al., 2018]] ). Projections indicate that the Amazon will be one of the regions in the world with the highest increase in fire weather indices over the 21st century and under all RCPs ( ''high confidence'' ) ( [[#Betts--2015|Betts et al., 2015]] ; [[#Abatzoglou--2019|Abatzoglou et al., 2019]] ; Q. [[#Sun--2019|]] [[#Sun--2019|]] [[#Sun--2019|Sun et al., 2019]] ). This is consistent with the large increase in the frequency of joint occurrence of extreme hot and dry days projected for a 2°C warming level or more ( [[#Vogel--2020|Vogel et al., 2020]] ). Projections of fire weather indices also show an increased risk in SWS ( ''high confidence'' ), SSA and SCA ( ''medium confidence'' ). However, wildfires highly depend on land use and appropriate management may help mitigate future increases in fire risk ( [[#Fonseca--2019|Fonseca et al., 2019]] ).

'''Mean precipitation is projected to change in a dipole pattern with increases in NWS and SES and decreases in NES and SWS''' ( high confidence ''') with further decreases in NSA and SCA''' ( medium confidence '''). There is''' medium confidence '''of an increase in river floods in SAM and SES. There is''' high confidence '''of an increase in drought duration in NES, an in the number of dry days and drought frequency in NSA and SAM. Dry climatic impact-drivers are projected to increase at the regional level with higher global warming levels. The strongest signal of future increase in agricultural and ecological drought, aridity and fire weather is over the Amazon region''' ( '''high confidence''' ''').'''

<div id="12.4.4.3" class="h3-container"></div>

<span id="wind-4"></span>