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We analyze the characteristics of atmospheric variations over tropical South America using the pattern recognition framework of weather typing or atmospheric circulation patterns (CPs). During 1979-2020, nine CPs are defined in the region, using a k-means algorithm based on daily unfiltered 850 hPa winds over 0035°N-30°S, 90°W-30°W. CPs are primarily interpreted as stages of the annual cycle of the low-level circulation. We identified three “winter” CPs (CP7, CP8 and CP9), three “summer” CPs (CP3, CP4 and CP5) and three “transitional” CPs (CP1, CP2 and CP6). Significant long-term changes are detected during the dry-to-wet transition season (July-October) over south tropical South America (STSA). One of the wintertime patterns (CP9) increases from 20% in the 1980s to 35% in the last decade while the “transitional” CP2 decreases from 13% to 7%. CP9 is characterized by enhancement of the South American Low-Level Jet and increasing atmospheric subsidence over STSA. CP2 is characterized by southerly cold-air incursions and anomalous convective activity over STSA. The years characterized by high (low) frequency of CP9 (CP2) during the dry-to-wet transition season are associated with a delayed South American Monsoon onset and anomalous dry conditions over STSA. Consistently, a higher frequency of CP9 intensifies the fire season over STSA (1999-2020). Over the Brazilian states of Maranhão, Tocantins, Goiás and São Paulo, the seasonal frequency of CP9 explains around 35%-44% of the interannual variations of fire counts.

Northern South America is among the regions with the highest vulnerability to climate change. General Circulation Models (GCMs) are among the different tools considered to analyze the impacts of climate change. In particular, GCMs have been proved to provide useful information, although they exhibit systematic biases and fail in reproducing regional climate, particularly in terrains with complex topography. This work evaluates the performance of GCMs included in the fifth and sixth phases of the Coupled Model Intercomparison Project (CMIP), representing the annual cycle of precipitation and air surface temperature in Colombia. To evaluate this, we consider different observational and reanalysis datasets, including in situ gauges from the Colombian Meteorological Institute. Our results indicate that although the most recent generation of GCMs (CMIP6) show improvements with respect to the previous generation (CMIP5), they still have systematic biases in representing the Intertropical Convergence Zone and elevation-dependent processes, which highly determine intra-annual precipitation and air surface temperature in Colombia. In addition, CMIP6 models have larger biases in temperature over the Andes than CMIP5. We also analyze climate projections by the end of the 21st century according to the CMIP5/CMIP6 simulations under the highest greenhouse gases emission scenarios. Models show projections toward warmer air surface temperatures and mixed changes of precipitation, with decreases of precipitation over the Orinoco and Colombian Amazon in September-November and increases over the eastern equatorial Pacific during the entire year.

The Andes is the most biodiverse region across the globe. In addition, some of the largest urban areas in South America are located within this region. Therefore, ecosystems and human population are affected by hydroclimate changes reported at global, regional and local scales. This paper summarizes progress of knowledge about long-term trends observed during the last two millennia over the entire Andes, with more detail for the period since the second half of the 20th century, and presents a synthesis of climate change projections by the end of the 21st century. In particular, this paper focuses on temperature, precipitation and surface runoff in the Andes. Changes in the Andean cryosphere are not included here since this particular topic is discussed in other paper in this Frontiers special issue, and elsewhere (e.g. IPCC,2019b). While previous works have reviewed the hydroclimate of South America and particular sectors (i.e., Amazon and La Plata basins, the Altiplano, Northern South America, etc.) this review includes for the first time the entire Andes region, considering all latitudinal ranges: tropical (North of 27°S), subtropical (27°S−37°S) and extratropical (South of 37°S). This paper provides a comprehensive view of past and recent changes, as well as available climate change projections, over the entire Andean range. From this review, the main knowledge gaps are highlighted and urgent research necessities in order to provide more mechanistic understanding of hydroclimate changes in the Andes and more confident projections of its possible changes in association with global climate change. Fil: Pabón Caicedo, José Daniel. Universidad Nacional de Colombia; Colombia Fil: Arias, Paola A.. Universidad de Antioquia; Colombia Fil: Carril, Andrea Fabiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina Fil: Espinoza, Jhan Carlo. Universite Grenoble Alpes; Francia Fil: Fita Borrell, Lluís. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina Fil: Goubanova, Katerina. Centro de Estudios Avanzados en Zonas Áridas; Chile Fil: Lavado Casimiro, Waldo. No especifíca; Fil: Masiokas, Mariano Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Solman, Silvina Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina Fil: Villalba, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina

Several studies have identified a recent lengthening of the dry season over the southern Amazon during the last three decades. Some explanations to this lengthening suggest the influence of changes in the regional circulation over the Atlantic and Pacific oceans, whereas others point to the influence of vegetation changes over the Amazon rainforest. This study aims to understand the implications of more frequent long dry seasons in this forest on atmospheric moisture transport toward northern South America and the Caribbean region. Using a semi-Langrangian model for water vapor tracking, results indicate that longer dry seasons in the southern Amazon relate to reductions of water vapor content over the southern and eastern Amazon basin, due to significant reductions of evaporation and recycled precipitation rates in these regions, especially during the transition from dry to wet conditions in the southern Amazon. On the other hand, longer dry seasons also relate to enhanced atmospheric moisture content over the Caribbean and northern South America regions, mainly due to increased contributions of water vapor from oceanic regions and the increase of surface moisture convergence over the equatorial region. This highlights the importance of understanding the relative role of regional circulation and local surface conditions on modulating water vapor transport toward continental regions.

Resumen Se analizó la posible influencia del fenómeno de El Niño-Oscilación del Sur (ENOS) en la variabilidad espacio-temporal de la precipitación en Colombia a partir de registros de estaciones in situ durante el período 1970-2015 y de datos provenientes de registros satelitales disponibles a partir de 1998. Mediante los índices de temperatura superficial del mar (TSM) asociados al fenómeno ENOS, se evaluaron las anomalías en la precipitación por trimestre para cada tipo de evento, así como las correlaciones mensuales simultáneas y rezagadas entre cada índice y las anomalías en la precipitación. Con base en la información satelital se concluyó que en gran parte del país hubo una mayor precipitación durante los eventos de La Niña Modoki que durante La Niña Canónica en el trimestre de diciembre, enero y febrero, en tanto que la precipitación disminuyó más en la fase canónica de El Niño que en la fase Modoki. La significación estadística de las correlaciones rezagadas evidenció la influencia de la TSM del Pacífico este en las anomalías en la precipitación en Colombia con un rezago de 0 hasta 6 meses. Los resultados de este trabajo aportaron una mayor claridad sobre las variaciones de la distribución de la precipitación y la disponibilidad de agua en Colombia durante las diversas fases del fenómeno de ENOS, lo cual contribuye a la búsqueda de un manejo más eficiente del recurso hídrico. © 2019. Acad. Colomb. Cienc. Ex. Fis. Nat. Abstract The possible influence of the El Niño-Southern Oscillation (ENSO) phenomenon on the spatiotemporal variability of the precipitation in Colombia is analyzed considering precipitation records from rain gauge dataset during the period 1970-2015, as well as records from satellite datasets available for the period 1998 to present. Based on sea surface temperature indexes associated with the ENSO phenomenon, we evaluated seasonal rainfall anomalies for each type of ENSO event, as well as monthly simultaneous and lagged correlations between ENSO indexes and precipitation anomalies. Results from the satellite data showed that there was more precipitation during La Niña Modoki than during the Canonical La Niña events in most of the country for the December-February period, while there was a larger reduction of precipitation during the canonical events of El Niño than the Modoki events. The statistical significance of lagged correlations showed that there was an influence of the surface temperature anomalies over the eastern Pacific region on precipitation in Colombia for a lag of 0 up to 6 months. This paper provides new insights about variations of precipitation distribution and water availability in Colombia during the different phases of ENSO, which is important for the efficient management of water resources in the region. © 2019. Acad. Colomb. Cienc. Ex. Fis. Nat.

El objetivo de este artículo fue analizar la influencia de dos tipos de eventos de El Niño, conocidos como Canónico y Modoki, en las corrientes superficiales de chorro del Chocó y el Caribe, importantes mecanismos de transporte de humedad y generación de precipitación en Colombia. La influencia de estos tipos de eventos de El Niño en las corrientes superficiales de interés se examinó con base en las diferencias entre las características en la climatología de estos chorros durante dichos eventos y el análisis de correlaciones entre estos fenómenos. Los resultados obtenidos indicaron que en los dos primeros trimestres del año, la intensidad de estas corrientes superficiales se ve disminuida durante ambos tipos de eventos El Niño, en tanto que en los dos últimos trimestres del año se observan efectos contrarios: un fortalecimiento del chorro del Caribe y un debilitamiento del chorro del Chocó. Sin embargo, la magnitud del impacto durante los eventos El Niño Modoki es menor que durante los eventos El Niño Canónico, aunque se observa un mayor número de eventos El Niño Modoki durante el periodo de análisis. Lo anterior es fundamental para la elaboración de pronósticos de precipitación en Colombia. The objective of this paper was to analyze the influence of two types of El Niño events (known as Canonical and Modoki) on the Chocó and the Caribbean low-level jets, which are important moisture transport and precipitation generation mechanisms in Colombia. We explored the influence of these types of El Niño events on these low-level jets by analyzing the differences between climatological features of these jets and the patterns observed during the occurrence of these two El Niño events, as well as the correlations between these phenomena. Our results indicated that for the first half of the year, the strength of these low-level jets diminished during the occurrence of both types of events, while in the last half of the year opposite effects were observed, with the strengthening of the Caribbean low-level jet and the weakening of the Choco jet during the occurrence of both events. However, the magnitude of the impacts observed during Canonical El Niño events was larger than during El Niño Modoki events. This finding Ciencias de la Tierrais essential in the development of rainfall forecasting in Colombia.

In this paper we assess South American monsoon system (SAMS) variability in the last millennium as depicted by global coupled climate model simulations. High-resolution proxy records for the South American monsoon over this period show a coherent regional picture of a weak monsoon during the Medieval Climate Anomaly and a stronger monsoon during the Little Ice Age (LIA). Due to the small external forcing during the past 1000 years, model simulations do not show very strong temperature anomalies over these two specific periods, which in turn do not translate into clear precipitation anomalies, in contrast with the rainfall reconstructions in South America. Therefore, we used an ad hoc definition of these two periods for each model simulation in order to account for model-specific signals. Thereby, several coherent large-scale atmospheric circulation anomalies are identified. The models feature a stronger monsoon during the LIA associated with (i) an enhancement of the rising motion in the SAMS domain in austral summer; (ii) a stronger monsoon-related upper-tropospheric anticyclone; (iii) activation of the South American dipole, which results in a poleward shift of the South Atlantic Convergence Zone; and (iv) a weaker upper-level subtropical jet over South America. The diagnosed changes provide important insights into the mechanisms of these climate anomalies over South America during the past millennium.

Spatiotemporal conditions that rule hydro-climatology over northern South America and the Caribbean Sea are influenced by a large amount of phenomena taking place at different timescales. Characterizing the activity of the AEWs over northern South America and the Caribbean is an imperative work to do in order to improve our understanding of the tropical atmospheric dynamics involved in hydrology and climate features over the region. The latter regulates the availability of very important resources such as water. Furthermore, AEWs activity plays an important role on air quality characteristics as a consequence of its connections with dust transport. In order to approach an adequate characterization of the AEWs activity over the region, this work addresses the relationship between these atmospheric perturbations and the occurrence or inhibition of precipitation, as well as possible connections with dust transport, when the AEW’s oscillations take place over northern South America and the Caribbean region. In particular, relative vorticity and outgoing long-wave radiation are used to identify AEW’s activity during the 1983–2013 period, together with daily precipitation anomalies, surface divergence, vertical integrated moisture flux, and Aerosol Optical Depth, in order to understand how the passage of AEWs could influence meteorological interactions in the region.

Spanish Abstract: Se analiza la posible influencia de las fases Canonica y Modoki del fenomeno El Nino-Oscilacion del Sur (ENSO) en la variabilidad espacio-temporal de la precipitacion en Colombia, a partir de registros de precipitacion de estaciones in situ que cubren el periodo 1970-2015 y de datos provenientes de registros satelitales disponibles a partir de 1998. Mediante indices de temperatura superficial del mar (TSM) asociados al fenomeno ENSO, se evaluan las anomalias de precipitacion por trimestre para cada tipo de evento, asi como correlaciones mensuales rezagadas entre cada indice y las anomalias de precipitacion. Se encuentra que cada uno de los eventos del fenomeno ENSO tiene influencia clara en el regimen de precipitacion para el trimestre Diciembre-Enero-Febrero. Durante los trimestres Junio-Julio-Agosto y Septiembre-Octubre-Noviembre, las correlaciones negativas ocurren en la zona norte y parte del area Andina, mientras que hacia el sur hay tendencia a correlaciones positivas durante estos eventos. La significancia de las correlaciones rezagadas muestra que hay influencia del fenomeno ENSO en la precipitacion, para un rezago de 0 hasta 6 meses. Este trabajo aporta a una mayor claridad sobre las variaciones de la distribucion de la precipitacion y la disponibilidad de agua en Colombia durante la ocurrencia de eventos ENSO, lo que es importante en la busqueda de un manejo mas eficiente del recurso hidrico y en particular, para la operacion de las redes de abastecimiento de agua en el pais. English Abstract: The possible influence of the canonical and Modoki phases of El Nino-Southern Oscillation (ENSO) on the spatiotemporal variability of the precipitation in Colombia is analysed by using precipitation records from rain gauge dataset during the period 1970-2015, as well as records from satellite datasets available for the period 1998 to present. Based on sea surface temperature indexes associated with the ENSO phenomenon, we evaluated seasonal rainfall anomalies for each type of ENSO events, as well as monthly lagged correlation between ENSO indexes and precipitation anomalies. Results show that each of the ENSO events has clear influence on precipitation during winter. The negative correlations occur in the north and Andean area during summer and autumn, while the positive correlations are located in the south of the country. The statistical significance of lagged correlations shows that there is influence of ENSO phenomenon on precipitation for a lag of 0 up to 6 months. This paper provides new insights about variations of precipitation distribution and water availability in Colombia during ENSO events, which is important in order to acquire a more efficient management of water resources in the region, and in particular for the operation of the water networks in the country.

Northern South America is identified as one of the most vulnerable regions to be affected by climate change. Furthermore, recent extreme wet seasons over the region have induced socioeconomic impacts of wide proportions. Hence, the evaluation of rainfall simulations at seasonal and interannual time scales by the CMIP5 models is urgently required. Here, we evaluated the ability of seven CMIP5 models (selected based on literature review) to represent the seasonal mean precipitation and its interannual variability over northern South America. Our results suggest that it is easier for models to reproduce rainfall distribution during boreal summer and fall over both oceans and land. This is probably due to the fact that during these seasons, incoming radiation and ocean-atmosphere feedbacks over Atlantic and Pacific oceans locate the ITCZ on the Northern Hemisphere, as suggested by previous studies. Models exhibit the worse simulations during boreal winter and spring, when these processes have opposite effects locating the ITCZ. Our results suggest that the models with a better representation of the oceanic ITCZ and the local low-level jets over northern South America, such as the Choco low-level jet, are able to realistically simulate the main features of seasonal precipitation pattern over northern South America.

Using hourly records from 51 rain gauges, spanning between 22 and 28 yr, the authors study the diurnal cycle of precipitation over the tropical Andes of Colombia. Analyses are developed for the seasonal march of the diurnal cycle and its interannual variability during the two phases of El Niño–Southern Oscillation (ENSO). Also, the diurnal cycle is analyzed at intra-annual time scales, associated with the westerly and easterly phases of the Madden–Julian oscillation, as well as higher-frequency variability (