A weeklong workshop in Brazil in August 2004 provided the opportunity for 28 scientists from southern South America to examine daily rainfall observations to determine changes in both total and extreme rainfall. Twelve annual indices of daily rainfall were calculated over the period 1960 to 2000, examining changes to both the entire distribution as well as the extremes. Maps of trends in the 12 rainfall indices showed large regions of coherent change, with many stations showing statistically significant changes in some of the indices. The pattern of trends for the extremes was generally the same as that for total annual rainfall, with a change to wetter conditions in Ecuador and northern Peru and the region of southern Brazil, Paraguay, Uruguay, and northern and central Argentina. A decrease was observed in southern Peru and southern Chile, with the latter showing significant decreases in many indices. A canonical correlation analysis between each of the indices and sea surface temperatures (SSTs) revealed two large-scale patterns that have contributed to the observed trends in the rainfall indices. A coupled pattern with ENSO-like SST loadings and rainfall loadings showing similarities with the pattern of the observed trend reveals that the change to a generally more negative Southern Oscillation index (SOI) has had an important effect on regional rainfall trends. A significant decrease in many of the rainfall indices at several stations in southern Chile and Argentina can be explained by a canonical pattern reflecting a weakening of the continental trough leading to a southward shift in storm tracks. This latter signal is a change that has been seen at similar latitudes in other parts of the Southern Hemisphere. A similar analysis was carried out for eastern Brazil using gridded indices calculated from 354 stations from the Global Historical Climatology Network (GHCN) database. The observed trend toward wetter conditions in the southwest and drier conditions in the northeast could again be explained by changes in ENSO.

A comprehensive view is given of the precipitation and circulation anomalies associated with the various stages of El Niño (EN) and La Niña (LN) events all over southern South America (SSA). This view comprises the delineation of coherent regions with respect to precipitation anomalies, the identification of the seasons of maximum anomalies, the indication of their magnitude, and the assessment of their consistency during those events. In addition, the spatial and temporal variability of these anomalies is detailed by calculating the expected precipitation percentiles and the consistency of wet and dry anomalies for each station and each three-month running season during EN and LN events. Composites of circulation anomalies and an assessment of their consistency are also presented and their connection with the precipitation anomalies is discussed. Southern Brazil presents the strongest average signal in EN events. The general behavior toward opposite signals in the precipitation and circulation anomalies over SSA during almost the same periods of the EN and LN events indicates a large degree of linearity in the response to these events. The timing of the anomalies changes throughout SSA, leading to the identification of eight different coherent regions in the EN case and six in the LN case. This regionalization is mostly caused by different processes leading to precipitation anomalies in SSA during those events. All these regions show a significant response in some part of each event. The magnitude and consistency of this response show a large spatial variability and some areas present very strong and consistent anomalies sometimes not disclosed when large coherent regions are analyzed. In spite of the differences in timing, some features of the precipitation anomalies are rather uniform throughout the region during EN and LN events. In EN episode, there is a tendency to lower than median precipitation in the year before the event, which continues until March of the year of the event. In a vast region, east of the Andes, the strongest positive precipitation anomalies occur in spring of this year, when the circulation anomalies concur to enhance rainfall over several regions. During the summer of the mature stage the positive precipitation anomalies almost disappear and then reappear in some regions in late summer-early autumn and in winter of the year following the starting year of the event. This description holds partially for the LN event, but with opposite signs, although there is a larger spatial variability in the LN-related anomalies in the following year and some shifts in timing. As for precipitation, the symmetry of the geopotential height anomaly fields with opposite signs between LN and EN cases is also remarkable, especially during the year (0).

Para citar este documentoRabelo da Rocha Repinaldo, C.., Müller, G. V., Martins Andrade, K.. (2017). Patrones atmosfericos simulados en el clima presente y futuro asociados al descenso de temperatura en el sudeste de Sudamerica. Boletín geográfico, 39, 13-34. ResumenLas características atmosféricas asociadas a eventos extremos fríos, identificados a partir del descenso de la temperatura en el invierno en tres regiones en el sudeste de Sudamérica, son analizadas con datos de reanálisis NCEP/NCAR y simulaciones de los modelos HadCM3 y GFDL-CM2.0 en la versión acoplada océano-atmósfera, para el clima presente y el escenario futuro más crítico A2 del CMIP3. Para las simulaciones del clima presente, el modelo que mejor representó las características observadas en el conjunto del reanálisis fue el GFDL-CM2.0, presentándose más coherente con relación a las posiciones de las altas pos frontales y de las isotermas de 0°C y 10°C. Para el futuro, el modelo GFDL-CM2.0 proyecta un debilitamiento de las anomalías negativas de temperatura y los eventos extremos de caída de temperatura con menos avance en dirección al Ecuador, mientras que, según el modelo HadCM3, la simulación para el futuro

In most of Argentina, the warming since 1901 was a little lower than the global average, although with strong trends in temperature extremes and in heat waves during the most recent decades. There was a remarkable increase in precipitation over most of subtropical Argentina, especially since 1960. This has favored agriculture yields and the extension of crop lands into semiarid regions, but this increase also came with more frequent heavy rainfalls and consequent flooding of rural and urban areas. Since the early 1970s, the main rivers of the Plata Basin have increased their mean flows, but this was attributable not only to increased precipitation, but also to land use changes. In contrast, over the Andes Mountains, reduced rainfall and increased temperature has led to glaciers receding and reduced river flows. Climate projections for the first half of this century maintain observed trends and raise additional concerns that in most cases can be dealt with timely adaptation policies. However, by the end of this century, under an extreme emissions scenario, the projected warming reaches 3.5°C in the north of the country with respect to present‐day conditions. There is insufficient knowledge to assume that this warming would not create severe damages to the people and the economy of Argentina. Because of the damages and casualties that heat waves and extreme precipitation events are already producing, the first and most urgent adaptation required is to reinforce early warning systems and contingency planning to cope with climatic extremes and their consequences on health. WIREs Clim Change 2015, 6:151–169. doi: 10.1002/wcc.316 This article is categorized under: Trans‐Disciplinary Perspectives > National Reviews

in the economies of the region. It is a primary factor in energy production, water resources, transportation, agriculture, and livestock. Of particular interest was the evaluation of the annual cycle of the hydrologic cycle components. The La Plata annual-mean river discharge is about 21 000 m3 s21, and the amplitude of its mean annual cycle is small: it is slightly larger during late summer, but continues with large volumes even during winter. The reason for this is that different precipitation regimes over different locations contribute to the total river discharge. One regime is found toward the northern boundary, where precipitation peaks during summer in association with the southernmost extension of the monsoon system. A second one is found over the central part of the basin, where precipitation peaks at different times in the seasonal cycle. Further analysis of the main tributaries of La Plata (Parana´, Uruguay, and Paraguay) reveals that each has a well-defined annual cycle but with different phases that can be traced primarily to each basin's physiography and precipitation regime. Interannual and interdecadal variability of the basin's precipitation is amplified in the variability of streamflow by a factor of 2, implying a high sensitivity of the hydrologic system to climate changes like those observed in the last few decades. This becomes more important when considering the large variability of streamflow: for example, the historical maxima of river discharge during the year following the onset of El Nin˜o can triple the typical mean river discharge. A crucial component of the atmospheric water cycle, the low-level jet east of the Andes, supplies moisture from tropical South America to La Plata basin throughout the year. In lower latitudes, the jet has the greatest intensity during summer, but south of about 158S there is a phase shift and the largest moisture fluxes are found during winter and spring. This is an uncommon feature not observed in other regions like the Great Plains of the United States, where the low-level jet develops only during the warm season.

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This Intergovernmental Panel on Climate Change Special Report (IPCC-SREX) explores the challenge of understanding and managing the risks of climate extremes to advance climate change adaptation. Extreme weather and climate events, interacting with exposed and vulnerable human and natural systems, can lead to disasters. Changes in the frequency and severity of the physical events affect disaster risk, but so do the spatially diverse and temporally dynamic patterns of exposure and vulnerability. Some types of extreme weather and climate events have increased in frequency or magnitude, but populations and assets at risk have also increased, with consequences for disaster risk. Opportunities for managing risks of weather- and climate-related disasters exist or can be developed at any scale, local to international. Prepared following strict IPCC procedures, SREX is an invaluable assessment for anyone interested in climate extremes, environmental disasters and adaptation to climate change, including policymakers, the private sector and academic researchers.