Impacts of teleconnection patterns on South America climate

Reduced rainfall over the Amazon basin in an idealized CO2 removal scenario: Remote dynamic processes

The Amazon basin plays a crucial role in biodiversity and carbon storage, but its local rainfall is anticipated to decrease under global warming. Carbon dioxide removal (CDR) is being considered as a method to mitigate the impact of global warming. However, the specific effects of CDR on Amazon rainfall have not been well understood. Here, an idealized CDR experiment reveals that the reduced rainfall over the Amazon basin does not recover. Significantly weaker rainfall is found during the ramp-down period compared to the ramp-up period at the same CO2 concentration. This response is associated with the enhanced El Niño-like warming in the tropical Pacific Ocean during the CDR period. This warming pattern has dual effects: weakening the zonal circulation and causing anomalous descent directly over the Amazon basin, while also triggering a stationary Rossby wave train that propagated downstream and generated anomalous ascent over the Sargasso Sea. This anomalous ascent induces anomalous descent and weakens moisture transport over the Amazon basin by the local meridional circulation. Consequently, precipitation is reduced over the Amazon basin in response to the weakened zonal and meridional circulation. Our findings indicate that even if the atmospheric CO2 concentration is lowered, the Amazon basin will remain susceptible to drought. Effective local climate adaptation strategies are urgently needed to address the vulnerability of this critical ecosystem.

The effects of teleconnections on water and carbon fluxes in the two South America's largest biomes

Ecosystem services provided by terrestrial biomes, such as moisture recycling and carbon assimilation, are crucial components of the water, energy, and biogeochemical cycles. These biophysical processes are influenced by climate variability driven by distant ocean-atmosphere interactions, commonly referred to as teleconnections. This study aims to identify which teleconnections most significantly affect key biophysical processes in South America's two largest biomes: The Amazon and Cerrado. Using 20 years of monthly data on Precipitation (P), Evapotranspiration (ET), Gross Primary Productivity (GPP), and Ecosystem Water Use Efficiency (EWUE), alongside data from six teleconnections (Antarctic Oscillation - AAO, Atlantic Multidecadal Oscillation - AMO, Oceanic Niño Index - ONI, Atlantic Meridional Mode - AMM, North Atlantic Oscillation - NAO, and Pacific Decadal Oscillation - PDO), we developed a multivariate linear model to assess the relative importance of each teleconnection. Additionally, time-lagged Spearman correlations were used to explore relationships between biophysical variables and teleconnections. Our findings indicate that the AMO exerts the strongest influence across all studied variables. Furthermore, ONI and AMM significantly impact precipitation in the northern Amazon, with a 3-month lag in ONI showing positive correlations with ET and GPP. In contrast, a 3-month lag in AMO negatively influences GPP in the southern Amazon and Cerrado, though positive correlations with EWUE were observed in the same region. These insights highlight the complex and regionally varied impacts of teleconnections on South America's largest biomes.

Temporal variability of spatial patterns of correlations between summer rainfall and the Oceanic Niño Index in the Pampean region

The Argentinean Pampean region is essential for global food security, known for its extensive production of soybeans, corn, and wheat. The November to January (NDJ) trimester is critical for rainfed summer crops, as precipitation during this period directly affects soil moisture and crop yields. The El Niño-Southern Oscillation (ENSO), particularly its Oceanic Niño Index (ONI), plays a crucial role in influencing precipitation patterns in this region. This study investigates the spatial correlation between the ONI and NDJ precipitation from 1990 to 2021 sing a 20-year sliding window approach. We conducted Pearson correlation and cluster analyses to identify regions with consistent ONI-precipitation relationships. Our findings reveal notable temporal variability, with a general decrease in correlation strength since the window 1995-2014. This decline is likely driven by changes in ENSO dynamics and the influence of other climate variability modes, highlighting the need to consider factors modulating the ONI-precipitation relationship. Notably, the addition of the strong 2015 El Niño, which exhibited inconsistent precipitation behaviour compared to previous strong El Niño events such as 1997, contributed to this weakening. While the 1997 El Niño brought widespread positive rainfall anomalies, the 2015 event was marked by weaker and even negative precipitation anomalies in part of the region. This difference mirrors similar patterns reported in other parts of South America, such as Ecuador and Coastal Peru, and may be linked to a poleward shift in the jet streams during the 2015/2016 El Niño. The results underscore the complexity of ENSO's impact on regional climate and highlight the need for adaptive agricultural planning. By enhancing the understanding of ONI-precipitation dynamics, this study aims to improve long-term climate predictions and support sustainable agricultural practices in the Pampean region.

Pacific decadal oscillation and ENSO forcings of northerly low-level jets in South America

The hydrological cycle in South America during austral summer, including extreme precipitation and floods, is significantly influenced by northerly low-level jets (LLJs) along the eastern Andes. These synoptic weather events have been associated with three different types of LLJs (Central, Northern, and Andes) and are sensitive to remote large-scale forcings. This study investigates how tropical forcings related to El Niño/Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) regulate the duration and frequency of each LLJ type and their impacts on extreme precipitation. Our analysis reveals that ENSO and PDO are important in driving the variability of LLJs over the past 65 years. Specifically, the Central LLJ type is more prevalent during El Niño and Warm/Neutral PDO phases, leading to heightened extreme precipitation in southern South America. Conversely, La Niña years during Cold PDO phases tend to favor the Northern and Andes LLJs, which are associated with increased precipitation extremes in the western Amazon and southeastern South America. Central and Andes LLJs tend to persist longer during these favored conditions, causing more pronounced precipitation events in the areas under their influence. This study enhances our understanding of the influence of large-scale atmospheric forcings on the regional precipitation dynamics in South America.

Analysis of the interrelationship between precipitation and confirmed dengue cases in the city of Recife (Brazil) covering climate and public health information

Large-scale epidemics of arboviruses, such as dengue, have heightened societal awareness regarding the necessity of combating the primary transmission vectors. Equally critical is the identification of environmental conditions and variables that influence vector population dynamics. Aedes aegypti, the primary vector of arboviruses such as dengue and Zika in Brazil, is closely associated with the climatic and geographical conditions of urban environments. This study examines the relationship between precipitation and confirmed dengue cases in Recife (Brazil), employing regression and quantile analyses to evaluate the influence of meteorological conditions on the disease's spread. The findings reveal a direct correlation between monthly averages of precipitation and confirmed cases, although this is apparent only when excluding years of epidemic peaks. The highest number of cases generally aligns with the rainy season, and the lowest with the dry season, with weak, moderate and strong precipitation events being closely linked to increased dengue incidence. However, notable discrepancies were identified: four out of six major outbreaks occurred in drier months, challenging the assumption of a straightforward relationship between rainfall and dengue incidence. These findings underscore the multifaceted nature of dengue dynamics, suggesting that while precipitation plays a significant role, other factors, including serotype circulation and broader climatic phenomena, are equally critical in driving outbreaks. This complexity highlights the need for a more comprehensive understanding of the mechanisms influencing dengue epidemics.

Modulation of PM2.5 in tropical South America by the upper-level atmospheric circulation and El Niño-Southern Oscillation phases

In the Amazon basin, biomass burning has been identified as a major cause of poor regional air quality and the dominant source of particulate matter (PM). In this study, we analyse the impact of the upper-level jet on PM2.5 (PM with an aerodynamic diameter ≤ 2.5 μm) concentrations in tropical South America (SA) from December to February during the period 2003-2022. Furthermore, we investigate the response of air pollutants to the joint modulation by the upper-level jet and El Niño-Southern Oscillation (ENSO). We find that PM2.5 concentrations in north-eastern Brazil are reduced on days when the subtropical jet (STJ) is absent due to enhanced convection and precipitation over the region. This improvement in air quality is independent of the ENSO phase. Conversely, a prominent STJ inhibits convection and contributes to dry conditions that favour increased biomass burning and elevated pollutant concentrations. Furthermore, the co-occurrence of a prominent STJ with an El Niño phase acts synergistically to increase pollutant concentrations, as both reduce precipitation in north-eastern Brazil. In combination with La Niña, this upper-level pattern does not exert any modulation of the PM2.5 concentrations, as the wet conditions favoured by this ENSO phase prevail to reduce biomass burning.

Atmospheric circulation patterns associated with surface air temperature variability trends between the Antarctic Peninsula and South America

This study investigated the spatial patterns of atmospheric circulation associated with surface air temperature variability trends between the Antarctic Peninsula and South America, during the austral summer (1979-2020). The first mode shows a positive score trend, with warming in northern Antarctic Peninsula and southern South America. This mode is mainly associated with the positive/neutral Southern Annular Mode and La Niña phases. There is an anomalous low pressure in the Southeast Pacific, a strengthening (weakening) of the polar (subtropical) jet and a strengthening and/or south/southwest displacement of the South Atlantic Subtropical High, which can prevent the passage of transient systems over the continent. In addition, there is a negative phase pattern of the South Atlantic Dipole, which contributes to the strengthening of the South Atlantic Convergence Zone convective activity. The second mode shows a negative score trend, with cooling in the Antarctic Peninsula/southernmost South America and warming between 10-40°S over South America. This mode is mainly associated with the spatial pattern of Central Pacific El Niño. There is a strengthening of the low-level jet and a strengthening of the western branch of the South Atlantic Subtropical High, all of which contribute to the suppression of the South Atlantic Convergence Zone.

Climate teleconnections modulate global burned area

Climate teleconnections (CT) remotely influence weather conditions in many regions on Earth, entailing changes in primary drivers of fire activity such as vegetation biomass accumulation and moisture. We reveal significant relationships between the main global CTs and burned area that vary across and within continents and biomes according to both synchronous and lagged signals, and marked regional patterns. Overall, CTs modulate 52.9% of global burned area, the Tropical North Atlantic mode being the most relevant CT. Here, we summarized the CT-fire relationships into a set of six global CT domains that are discussed by continent, considering the underlying mechanisms relating weather patterns and vegetation types with burned area across the different world's biomes. Our findings highlight the regional CT-fire relationships worldwide, aiming to further support fire management and policy-making.

Heatwaves and fire in Pantanal: Historical and future perspectives from CORDEX-CORE

The Pantanal biome, at the confluence of Brazil, Bolivia and Paraguay, is the largest continental wetland on the planet and an invaluable reserve of biodiversity. The exceptional 2020 fire season in Pantanal drew particular attention due to the severe wildfires and the catastrophic natural and socio-economic impacts witnessed within the biome. So far, little progress has been made in order to better understand the influence of climate extremes on fire occurrence in Pantanal. Here, we evaluate how extreme hot conditions, through heatwave events, are related to the occurrence and the exacerbation of fires in this region. A historical analysis using a statistical regression model found that heatwaves during the dry season explained 82% of the interannual variability of burned area during the fire season. In a future perspective, an ensemble of CORDEX-CORE simulations assuming different Representative Concentration Pathways (RCP2.6 and RCP8.5), reveal a significant increasing trend in heatwave occurrence over Pantanal. Compared to historical levels, the RCP2.6 scenario leads to more than a doubling in the Pantanal heatwave incidence during the dry season by the second half of the 21st century, followed by a plateauing. Alternatively, RCP8.5 projects a steady increase of heatwave incidence until the end of the century, pointing to a very severe scenario in which heatwave conditions would be observed nearly over all the Pantanal area and during practically all the days of the dry season. Accordingly, favorable conditions for fire spread and consequent large burned areas are expected to occur more often in the future, posing a dramatic short-term threat to the ecosystem if no preservation action is undertaken.

A New Look into the South America Precipitation Regimes: Observation and Forecast

South America is a vast continent characterized by diverse atmospheric phenomena and climate regimes. In this context, seasonal climate predictions are helpful for decision-making in several relevant socioeconomic segments in this territory, such as agriculture and energy generation. Thus, the present work evaluates the performance of ECMWF-SEAS5 in simulating the South American precipitation regimes by applying a non-hierarchical clustering technique. In addition, the study describes the main atmospheric systems that cause precipitation in each cluster and updates a previous work performed in South America in 2010. As a result, ECMWF-SEAS5 simulates (with good correspondence) the eight climate regimes identified in the analysis of precipitation from the Climate Prediction Center (CPC). Moreover, ECMWF-SEAS5 has a satisfactory ability in representing the rainfall regime in low and medium climate predictability regions, such as central and southern South America. ECMWF-SEAS5 has good performance in the climate characterization of South America and it gives us confidence in using its seasonal climate predictions throughout the continent.

Potential fire risks in South America under anthropogenic forcing hidden by the Atlantic Multidecadal Oscillation

Fires in South America have profound effects on climate change and air quality. Although anthropogenic forcing has exacerbated drought and fire risks, the fire emissions and aerosol pollution in the southern Amazon and the Pantanal region showed a consistent long-term decrease during the dry season (August-October) between 2003 and 2019. Here, we find that the decreasing trend in fire emissions, mainly located in the non-deforested region, was associated with climatic conditions unfavorable for intensifying and spreading fires, including increased humidity and slower surface wind speed. These climatic trends can be attributed to weakening of the positive phase of the Atlantic Multidecadal Oscillation, which has strengthened the northeast trade winds within the region (3°S-13°N) and the northwest winds east of the Andes that transport more moisture into the southern Amazon and the Pantanal region. Our findings show the mitigating effects of weakening of the positive Atlantic Multidecadal Oscillation phase on human-induced intensification of fire risks in South America and warn of potentially increased risks of fires and aerosol pollution under intensified anthropogenic forcing in the future.

Drought Assessment in São Francisco River Basin, Brazil: Characterization through SPI and Associated Anomalous Climate Patterns

The São Francisco River Basin (SFRB) is one of the main watersheds in Brazil, standing out for generating energy and consumption, among other ecosystem services. Hence, it is important to identify hydrological drought events and the anomalous climate patterns associated with dry conditions. The Standard Precipitation Index (SPI) for 12 months was used to identify hydrological drought episodes over SFRB 1979 and 2020. For these episodes, the severity, duration, intensity, and peak were obtained, and SPI-1 was applied for the longest and most severe episode to identify months with wet and dry conditions within the rainy season (Nov–Mar). Anomalous atmospheric and oceanic patterns associated with this episode were also analyzed. The results revealed the longest and most severe hydrological drought episode over the basin occurred between 2012 and 2020. The episode over the Upper portion of the basin lasted 103 months. The results showed a deficit of monthly precipitation up to 250 mm in the southeast and northeast regions of the country during the anomalous dry months identified through SPI-1. The dry conditions observed during the rainy season of this episode were associated with an anomalous high-pressure system acting close to the coast of Southeast Brazil, hindering the formation of precipitating systems.