South American Monsoon System Research Articles

Changes in the South American Monsoon System components since the Last Glacial Maximum: a TraCE-21k perspective

Changes in the South American Monsoon System components since the Last Glacial Maximum: a TraCE-21k perspective

Where did the water come from? Wetlands and shallow lakes in semi‐arid dunefields from South America during the Pleistocene–Holocene transition

ABSTRACTStabilized and active dunes and sand sheet deposits abound in a small lake‐dotted semi‐arid region of the Western Pampean Dunefield, Argentina. Here, a multi‐scale and multi‐proxy study of three sites, across a hydrologic gradient from lakes to a dryland with groundwater levels at more than 25 m depth, analyzes calcareous and ferruginous rhizoliths, calcareous crusts, hypocoatings, pedogenic carbonate and amorphous Mn‐oxide precipitates within blowout dunes. These palustrine‐related features indicate significantly wetter conditions that allowed the development of shallow lakes and expanding wetlands during the Pleistocene–Holocene transition, limited by associated optically stimulated luminescence ages between ca. 14.7 and 11.6 ka. These wetter conditions, also identified in other nearby proxy records, may be associated with a strengthened South American Monsoon System, potentially during the Younger Dryas Chronozone, though other geological, ecological and climatic forcings cannot be ruled out with available data. Such a scenario lacks a modern analogue, since current hydrologic excess, evidenced in the formation of lakes and new rivers, is not observed in the localities which record paleolakes. This study underlines the variable conditions for pronounced hydrologic excess in semi‐arid eolian environments in western Argentina with complex ecological, anthropogenic and climatic linkages.

The South American Tropopause Aerosol Layer (SATAL)

Abstract The presence of an aerosol layer in the upper troposphere/lower stratosphere (UT/LS) in South America was identified with the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2). This layer, which we shall refer to as the South American tropopause aerosol layer (SATAL), was identified over the Amazon basin at altitudes between 11 and 14 km. It exhibits a seasonal behavior similar to the Asian tropopause aerosol layer (ATAL) and the North American tropopause aerosol layer (NATAL). The SATAL is observed from October to March, coinciding with the presence of the South American monsoon. It forms first in the eastern Amazon basin in October, then moves to the southern Amazon, where it weakens in December–January and finally dissipates in February–March. We hypothesize that two main factors influence the SATAL formation in the UT/LS: 1) the source of aerosols from Africa and 2) the updraft mass flux from deep convective systems during the active phase of the South American monsoon system that transports aerosols to the UT/LS. Further satellite observations of aerosols and field campaigns are needed to provide useful information to find the origin and composition of the aerosols in the UT/LS during the South American monsoon.

Holocene geochronology and sedimentation in the southern Brazil shelf depocenters

Latitudinal modulation of proxies for environmental changes over the mid to late-Holocene was analyzed in four cores retrieved along mud depocenters on the South Brazilian Shelf, between 33.8°S and 25.1°S. To the south, early to mid-Holocene northwards migrations of the Southern Westerly Wind Belt (SWWB) and the post-LGM sea level rise are expressed as an increase in sand content, while the low Ti/Ca and Ti/K ratios point to dry climatic conditions. During the mid-Holocene, the sea level highstand coincided with a period of stabilization in atmospheric conditions, which led to a pulse of coarser sediment deposition in the southern area. In 3000 cal yr BP, a rapid and latitudinally simultaneous increase of Ti/Ca and Ti/K mark the late-Holocene more humid and warmer onset linked to an intensification of the South American Monsoon System (SAMS). Across-shelf branches of the Brazil Current (BC) that mix with the Plata Plume Water (PPW) to flow northwards could be responsible for sediment remobilization leading to clay depletion in the south extreme of the study area. The amplitude of grain size changes gets lower as we go further north, suggesting a buffering effect exerted by the distance to the source.

Future Projections of Low‐Level Atmospheric Circulation Patterns Over South Tropical South America: Impacts on Precipitation and Amazon Dry Season Length

AbstractThe last few decades have shown evidence of a lengthening dry season in southern Amazonia, which is associated with a delay in the onset of the South American Monsoon System (SAMS). Using a pattern recognition framework of atmospheric circulation patterns (CPs), previous studies have identified specific atmospheric situations related to the onset of the SAMS. Here, we analyze the future changes in the CPs that largely define the main hydro‐climatological states of Tropical South America. We evaluated the CP changes that occurred between two periods: historical (1970–2000) and future (2040–2070), using six General Circulation Models (GCMs) from the Coupled Model Intercomparison Project Phase 6. Future GCM projections show significant spatio‐temporal changes in the CPs associated with the dry season in southern Amazonia during the mid‐21st century. These changes are related to both a late onset of the SAMS and an early demise of the SAMS. Particularly, the CP methodology allowed for a better understanding of the behavior of the southern Amazon dry season under future conditions, showing an increase in the frequency of the CPs typically observed during the dry season. The occurrence of dry days in the Amazon basin during the austral winter of the mid‐21st century increases by 19.4% on average, with respect to the historical period. This methodology also identified a future increase in the frequency of dry CPs, both at the beginning of the dry‐to‐wet transition period (8%) and at the end of the wet‐to‐dry transition season (11%).

The Influence of Southeastern South American Rainfall on Weather Patterns Over the Tropical Atlantic, Northwestern Africa and Western Europe

AbstractDuring boreal winter (December–February), the South American monsoon system (SAMS) reaches its annual maximum when upper‐tropospheric westerly winds prevail over the equatorial Atlantic. Atmospheric dynamic model simulations suggest that Rossby waves generated over South America can propagate to and potentially influence weather patterns in the Northern Hemisphere (NH). However, observational evidence has been absent previously. Here we focus on southeastern South American (SESA) precipitation anomalies, which can characterize intraseasonal rainfall variability of the SAMS. Since tropical “westerly duct” and convective heating are important factors for cross‐equatorial propagation of Rossby wave (CEPRW), we identify two groups of events based on the two factors. By comparing the events associated with both SESA rainfall and tropical westerlies to the events associated with tropical westerlies only, we find that an anomalous Rossby wave train is triggered by precipitation anomalies over SESA, propagates in the southwest–northeast direction, and subsequently crosses the equator. Over a period of 4 days, near‐surface temperature over northwestern Africa and western Europe becomes warmer, accompanied by increased surface downward longwave radiation and precipitable water. The equatorward propagating Eliassen–Palm flux anomalies originated from SESA support the evidence of CEPRW. Simulations using a time‐dependent linear barotropic model forced by prescribed divergence anomalies over SESA further confirm that SESA rainfall can influence the NH weather patterns through CEPRW. Knowledge of this study will help us better understand and model interhemispheric teleconnections over the American–Atlantic–African/European sector.

South American Monsoon Lifecycle Projected by Statistical Downscaling with CMIP6-GCMs

This study analyzed the main features (onset, demise, and length) of the South American Monsoon System (SAMS) projected in different time slices (2020–2039, 2040–2059, 2060–2079, and 2080–2099) and climate scenarios (SSP2–4.5 and SSP5–8.5). Eight global climate models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) that perform well in representing South America’s historical climate (1995–2014) were initially selected. Thus, the bias correction–statistical downscaling (BCSD) technique, using quantile delta mapping (QDM), was applied in each model to obtain higher-resolution projections than their original grid. The horizontal resolution adopted was 0.5° of latitude × longitude, the same as the Climate Prediction Center precipitation analysis used as a reference dataset in BCSD. The QDM technique improved the monsoon onset west of 60° W and the simulated demise and length in southwestern Amazonia. Raw and BCSD ensembles project an onset delay of approximately three pentads compared to the historical period over almost all regions and a demise delay of two pentads northward 20° S. Additionally, the BCSD ensemble projects a reduced length with statistical significance in most South Atlantic Convergence Zone regions and a delay of three pentads in the demise over the Brazilian Amazon from the second half of the 21st century.

Exploring monsoon precipitation signal in the Peruvian tropical montane cloud forest: Andean Walnut wood anatomy plasticity

Summary Andean Walnut (Juglans neotropica Diels-Juglandaceae) is a long-lived, deciduous broadleaf Tropical Montane Cloud Forest (TMCF) tree species native to the Andes Cordillera; nevertheless, it has received limited attention for dendro-quantitative wood anatomical studies. Based on 70 increment cores from 50 Andean Walnut trees at two Peruvian TMCFs, two chronologies (from 1969 to 2020 and from 1964 to 2020) were developed. The xylem vessel parameters assessment allowed us to detect South American Monsoon System (SAMS) precipitation signals in the Andean Walnuts’ wood. Dendro-wood anatomical features can be assessed within an annual growth ring, which allows for assessing intra-annual past and present wood anatomy-function relationships and its climate vulnerability.

Atlantic ITCZ variability during the Holocene based on high-resolution speleothem isotope records from northern Venezuela

Few high-resolution paleoclimate proxy records exist in the region located under the direct influence of the Intertropical Convergence Zone (ITCZ) in South America and most of them were retrieved from the Cariaco Basin off the coast of Venezuela. Here we present new ẟ18O and ẟ13C records of Venezuelan speleothems collected in caves adjacent to Cariaco, covering the mid- and late-Holocene. We document previously undetected secular-to multidecadal-scale climate variability in the core region of the ITCZ, which is compared to other high-resolution records from the North Atlantic, Caribbean and tropical South America. Over the mid-Holocene our record exhibits broad swings between periods of reduced (8.3–8.0, 6.5–5.0, 4.1–3.6 ka BP) and increased (8.5, 8.0–6.5, 4.9–4.2 ka BP) rainfall. In particular, between 5.5 and 5.0 ka BP, increases in polar and subpolar North Atlantic ice rafted debris and a reduction in North Atlantic Deep Water (NADW) formation might have contributed to the southward displacement of the North Atlantic Subtropical High (NASH) and the ITCZ, which led to severe dry conditions in north central Venezuela and an enhancement of the South American Monsoon System (SAMS). During the late-Holocene, contrary to data from Cariaco reported in previous studies, our results point to drier conditions during the Medieval Climate Anomaly (MCA, 900–1100 CE), which were further amplified during positive Atlantic Multidecadal Oscillation (AMO) phases. Wet conditions, however, prevailed during the first part of the Little Ice Age (LIA, 1400–1500 CE). No speleothem deposition occurred during the main LIA period, which might be related to drier conditions in response to a southward displacement of the ITCZ that led to major moisture convergence over the SASM domain. Our new records from Venezuela provide a reliable proxy for ITCZ behavior over the Atlantic – South America domain and document past dynamics in relation to other climate systems (NASH and SAMS), while providing new evidence of ITCZ – North Atlantic teleconnections during the Holocene.

Climate Patterns and Their Influence in the Cordillera Blanca, Peru, Deduced from Spectral Analysis Techniques

Climate patterns are natural processes that drive climate variability in the short, medium, and long term. Characterizing the patterns behind climate variability is essential to understand the functioning of the regional atmospheric system. Since investigations typically reveal only the link and extent of the influence of climate patterns in specific regions, the magnitude of that influence in meteorological records usually remains unclear. The central Peruvian Andes are affected by most of the common climate patterns of tropical areas, such as Intertropical Convergence Zone (ITCZ), Sea Surface Temperature (SST), solar irradiance, Madden Julian Oscillation (MJO), Pacific Decadal Oscillation (PDO), and El Niño Southern Oscillation (ENSO). They are also affected by regional processes that are exclusive from South America, such as the South American Low-Level Jet (SALLJ), South American Monsoon System (SAMS), Bolivian High (BH), and Humboldt Current. The aim of this research is to study the climate variability of precipitation, maximum and minimum temperature records over Cordillera Blanca (Peru), and its relationship with the intensity and periodicity of the common climate patterns that affect this region. To achieve this aim, a spectral analysis based on Lomb’s Periodogram was performed over meteorological records (1986–2019) and over different climate pattern indexes. Results show a coincidence in periodicity between MJO and SALLJ, with monthly cycles for precipitation and temperature (27-day, 56-day, and 90-day cycles). Moreover, the most intense periodicities, such as annual (365 days) and biannual (182 and 122 days) cycles in meteorological variables, possibly would be led by ITCZ and ENSO together, as well as a combination of the Humboldt Current and SALLJ. Additionally, interannual periodicities (3-year, 4.5-year, 5.6–7-year and 11-year cycles) would have coincidence with the ENSO–solar combination, while the longest cycles (16 years) could match PDO variability.

Hydroclimate variability in the Caribbean during North Atlantic Heinrich cooling events (H8 and H9)

We present a speleothem record from western Cuba, spanning the period 98.7–84.9 ka BP. Our record shows two distinctive periods of high δ18O corresponding to dry and/or cold periods during 85–87.6 and 90.2–93.1 ka BP, synchronous with Heinrich events 8 and 9 (H8 and H9). Hence, we provide the first proxy evidence of the local Caribbean climate response to H8 and H9. Interestingly, H8 is more pronounced compared to H9, which may be a local response to lower temperatures in the North Atlantic resulting in a weak AMOC and reduced deep water formation, therefore a stronger south shift of the ITCZ. Our data complement existing speleothem records from western Cuba which, collectively, provide a nearly continuous paleoclimate time-series spanning the last 100 ka BP, indicating a consistent response to millennial-scale events as dry and/or cooler conditions. The comparison with regional paleoclimate records reveals an anti-phased relationship with South America, caused by the southern movements of the ITCZ during millennial-scale events which lead to dry conditions in the Caribbean and a stronger South American Monsoon System.

Water-Vapour Monitoring from Ground-Based GNSS Observations in Northwestern Argentina

The Central Andes in northwestern Argentina are characterized by steep topographic and climatic gradients. The humid foreland areas at 1 km asl elevation rapidly rise to over 5 km in the eastern Cordillera, and they form an orographic rainfall barrier on the eastern windward side. This topographic setting combined with seasonal moisture transport through the South American monsoon system leads to intense rainstorms with cascading effects such as landsliding and flooding. In order to better quantify the dynamics of water vapour transport, we use high-temporal-resolution global navigation satellite system (GNSS) remote sensing techniques. We are particularly interested in better understanding the dynamics of high-magnitude storms with high water vapour amounts that have destructive effects on human infrastructure. We used an existing GNSS station network with 12 years of time series data, and we installed two new ground stations along the climatic gradient and collected GNSS time series data for three years. For several stations we calculated the GNSS signal delay gradient to determine water vapour transport direction. Our statistical analysis combines in situ rainfall measurements and ERA5 reanalysis data to reveal the water vapour transport mechanism for the study area. The results show a strong relationship between altitude and the water vapour content, as well as between the transportation pathways and the topography.

Evaluation of the CMIP6 Performance in Simulating Precipitation in the Amazon River Basin

The Brazilian Amazon provides important hydrological cycle functions, including precipitation regimes that bring water to the people and environment and are critical to moisture recycling and transport, and represents an important variable for climate models to simulate accurately. This paper evaluates the performance of 13 Coupled Model Intercomparison Project Phase 6 (CMIP6) models. This is done by discussing results from spatial pattern mapping, Taylor diagram analysis and Taylor skill score, annual climatology comparison, cumulative distribution analysis, and empirical orthogonal function (EOF) analysis. Precipitation analysis shows: (1) This region displays higher rainfall in the north-northwest and drier conditions in the south. Models tend to underestimate northern values or overestimate the central to northwest averages. (2) The southern Amazon has a more defined dry season (June, July, and August) and wet season (December, January, and February) and models simulate this well. The northern Amazon dry season tends to occur in August, September, and October and the wet season occurs in March, April, and May, and models are not able to capture the climatology as well. Models tend to produce too much rainfall at the start of the wet season and tend to either over- or under-estimate the dry season, although ensemble means typically display the overall pattern more precisely. (3) Models struggle to capture extreme values of precipitation except when precipitation values are close to 0. (4) EOF analysis shows that models capture the dominant mode of variability, which was the annual cycle or South American Monsoon System. (5) When all evaluation metrics are considered, the models that perform best are CESM2, MIROC6, MRIESM20, SAM0UNICON, and the ensemble mean. This paper supports research in determining the most up-to-date CMIP6 model performance of precipitation regime for 1981–2014 for the Brazilian Amazon. Results will aid in understanding future projections of precipitation for the selected subset of global climate models and allow scientists to construct reliable model ensembles, as precipitation plays a role in many sectors of the economy, including the ecosystem, agriculture, energy, and water security.

Dynamics of Precipitation Anomalies in Tropical South America

In this study, precipitation in Tropical South America in the 1931–2016 period is investigated by means of Principal Component Analysis and composite analysis of circulation fields. The associated dynamics are analyzed using the 20th century ERA-20C reanalysis. It is found that the main climatic processes related to precipitation anomalies in Tropical South America are: (1) the intensity and position of the South Atlantic Convergence Zone (SACZ); (2) El Niño Southern Oscillation (ENSO); (3) the meridional position of the Intertropical Convergence Zone (ITCZ), which is found to be related to Atlantic Sea Surface Temperature (SST) anomalies; and (4) anomalies in the strength of the South American Monsoon System, especially the South American Low-Level Jet (SALLJ). Interestingly, all of the analyzed anomalies are related to processes that operate from the Atlantic Ocean, except for ENSO. Results from the present study are in agreement with the state of the art literature about precipitation anomalies in the region. However, the added strength of the longer dataset and the larger study area improves the knowledge and gives new insights into how climate variability and the resulting dynamics are related to precipitation in Tropical South America.

Circulation Patterns and Associated Rainfall Over South Tropical South America: GCMs Evaluation During the Dry‐To‐Wet Transition Season

AbstractThe representation of the South American Monsoon System (SAMS) by general circulation models (GCMs) is of key relevance for a better understanding of the physical rationale behind the recent climate changes over South Tropical South America (STSA) and their expected changes in a global warming scenario. During the last four decades, STSA experienced a lengthening of the dry season associated with diverse forcings. In this work, a set of 16 GCMs historical Coupled Model Intercomparison Project Phase 6 coupled simulations were evaluated during 1979–2014 in terms of how well they reproduced the atmospheric circulation over STSA through a circulation‐patterns (CPs) approach. Nine CPs were first identified based on low‐level winds from the ERA5 reanalysis. Focus was put on the representation of CPs during the dry‐to‐wet transition season (July‐October). Model performance depended on the seasonal cycle and spatial structure of the CPs. GCMs adequately reproduced the different CPs, with lower skills in the transition seasons. GCMs tended to go from dry to wet conditions too quickly, evidencing deficiencies in the representation of the SAMS onset, related to a poor representation of the southerly wind intrusions to STSA and the variability of the South American low‐level jet. Some GCMs were able to associate the occurrence of anomalous dry and wet years with specific CPs, suggesting well‐represented physical mechanisms controlling precipitation variability. This study could identify a few GCMs that adequately simulated the CPs in STSA (among them, CESM2, CMCC‐CM2‐HR4 and MPI‐ESM1‐2‐HR), which is relevant for driving high‐resolution models and the analysis of future projections.

Late quaternary hydrological changes in the southeastern amazon basin from n-alkane molecular and isotopic records in sediments of Saci lake, Pará state (Brazil)

The molecular distributions and isotopic ratios (δ13C and δD) of n-alkanes in sediments deposited during the last 35 cal kyr BP in Saci Lake, southeastern Amazonia, have been measured and interpreted for their paleoclimate information. A terrestrial origin for the odd carbon-numbered long-chain (>C27) n-alkanes has been inferred from molecular distributions. A shift in the n-alkane δ13C values across the Pleistocene-Holocene boundary coincides with a climate-induced floral change previously deduced from palynological analyses. Dry conditions during the late Pleistocene and mid-Holocene were confirmed by several n-alkane indices used to estimate the availability of moisture and by larger δD values. High ACL values indicate relatively dry conditions from 29 to 18.2 cal kyr BP and again from 8.0 and 5.0 cal kyr BP with a decrease in precipitation and an increase of grasses. Changes in the n-alkane C-29 isotopic compositions (δD and δ13C) were observed during the Pleistocene-Holocene transition, coinciding with a floristic change induced by climatic conditions that is also observed in palynological results from the same lake. The n-alkane C-29 δ13C values remain between −33.2‰ and − 35.7‰, which is representative for n-alkanes derived from C3 vegetation. These lines of evidence suggest a continuous gallery forest cover in the Saci Lake catchment for the last ~35 cal kyr BP in contrasted with the observed palynological changes which represent the dynamics of the vegetation on the upland areas. The n-alkane C-29 δD values are less negative in the Pleistocene and more negative during the Holocene in the lake record. These characteristics suggest more humid conditions during the Holocene than in the Pleistocene, probably associated with the South American Monsoon System (SAMS). However, an increase of approximately 10‰ occurs during the late Holocene, which coincides with the forest expansion around 5 cal kyr BP that is recorded in palynological data of Saci Lake and other records of the Amazon Forest. This change suggests that the D/H ratio is also influenced by the increase of the plant biomass, which would provide an enrichment of D in the isotopic signal as a function of regional moisture recycling caused by evapotranspiration.

ITCZ precipitation and cloud cover excursions control Cedrela nebulosa tree-ring oxygen and carbon isotopes in the northwestern Amazon

The lack of delimitation between the South American Monsoon System (SAMS) and the Intertropical Convergence Zone (ITCZ) has led to problematic calibration of archives in paleoclimate studies, particularly in northern South America. We show for the first time recorded in a paleoclimate archive that the ITCZ is the primary controller of oxygen (δ18OTR) and carbon (δ13CTR) isotopes in Cedrela nebulosa tree-rings (1864–2018). In contrast, a monsoonal pattern is not observed at this latitude. Spatial correlations revealed that δ18OTR better reflects months of higher precipitation (Mar–Jun) in the western Amazon than local rainout processes at decadal time scale, owing to the strong convection in the basin at this time of the year. Similarly, this study identified cloud cover as a vital controller in sunshine duration, which influences the phenology of Cedrela nebulosa. We interpret the variability of the δ13CTR as an enhancement in the photosynthetic rate during light-increased months (Jul–Sep), strongly regulated by cloudiness reduction when the ITCZ rain band retreats to northwestern South America in austral winter. Overall, these results reveal that Cedrela nebulosa is well-adapted to wet environments, and its cellulose-based stable isotopic signals reflect the direct influence of the ITCZ excursions from austral autumn to winter (Mar–Sep) with minimal SAMS control.

Obliquity Influence on Low‐Latitude Coastal Precipitation in Eastern Brazil During the Past ∼850 kyr

AbstractPaleoclimate records from tropical South America typically show precession‐paced variability in rainfall, caused by insolation‐driven changes in the South American Monsoon System, however this mechanism may not be responsible for hydroclimate change outside of the core monsoon domain, such as in the coastal zone of tropical eastern Brazil. Our findings are based on a ∼850 kyr‐long multiproxy record from a marine sediment core collected from the eastern Brazilian margin that represents the longest continuous record of South American hydroclimate to date. Utilizing the ln (K/Al) chemical weathering proxy from the core, we determine that past hydroclimate change in the coastal zone was primarily modulated by obliquity forcing. We demonstrate that high obliquity is associated with an increase in the boreal summer interhemispheric insolation contrast which decreases the zonality of the southern trade winds and reduces moisture advection to the coastal zone. Based on the long‐term coherence between the ln (K/Al) record and benthic δ13C records from the Atlantic during Marine Isotope Stages 16–13, we infer that an increase in the strength of the overturning circulation, caused by Northern Hemisphere high‐latitude forcing, may have produced surface cooling in the western tropical South Atlantic which led to reduced moisture advection to the coastal zone. We suggest that this mechanism may have also caused the amplification in millennial‐scale variability in the coastal hydroclimate system, which began after the decoupling of the coastal hydroclimate system from obliquity forcing.

Paleoclimatic and paleoenvironmental changes in Amazonian lowlands over the last three millennia

The paleoclimatic and paleoenvironmental history of the Amazon basin over the last millennia and the behavior of the South American Monsoon System (SAMS) throughout the lowlands have not yet been thoroughly examined due to a lack of records from more central portions of the basin. Here we discuss these past changes based on new high-resolution δ18O and δ13C records from speleothems collected in the southwestern Amazon Basin, at the core region of the convective activity of the SAMS. We demonstrate that the δ18O from these new records is representative of SAMS variations and that this convective system provides distinct precipitation patterns over the basin. The SAMS was in a neutral phase with homogeneous precipitation between 1000 BCE and 300 CE, whereas drier conditions prevailed over the western side of the basin between 700 and 1200 CE and an east-west climatic dipole was established over the Amazon Basin after 1450 CE when wetter conditions prevailed over our study site. The speleothem δ13C record indicates an overall tendency toward a more humid tropical forest during the studied period, except for a drier period which correlates with the Medieval Climate Anomaly (MCA). The dynamics of pre-Columbian cultures from southwestern Amazonia seem to have been related to paleoclimatic and environmental changes reported for the region.

Uso de mapa auto-organizado para identificar padrões de precipitação e avaliar seu impacto em bacias hidrográficas no Brasil

ABSTRACT In this study, we used neural networks known as self-organizing maps (SOMs) to identify clusters of spatial synoptic precipitation patterns. These clusters were compared with the precipitation regime of the ten main hydrographic sub-basins in Brazil. Sixty years of daily precipitation data obtained from over 389 weather station in Brazil were used as input data for the SOMs, with a number of six clusters being prescribed as the optimal number according to the elbow and silhouette methods. The six precipitation patterns identified by the SOMs reflect the typical synoptic conditions associated mainly with the cold frontal systems (CF), South American Monsoon System (SAMS) and Inter-tropical Convergence Zone (ITCZ). In conclusion, SOMs perform well using interpolated precipitation data as the input data to identify synoptic precipitation patterns, which could be used to monitor the spatial distribution of precipitation, which affects the hydrographic basins in Brazil and hence hydropower plant performance.