Inés Camilloni

An Observed Trend in Central South American Precipitation

Abstract Seasonal linear trends of precipitation from South American station data, which have been averaged onto grids, are examined, with emphasis on the central continent. In the period 1976–99, the largest trend south of 20°S occurs during the January–March season, is positive, and is centered over southern Brazil. From 1948 to 1975 the trend is also positive, but with less than half the slope. The trend is not due to a systematic change in the timing of the rainy season, which almost always starts before January and usually ends after March, but rather results from an increase in the percent of rainy days, and an increase in the rainy day average. The dynamic causes of the trend are not obvious. It does not appear to be accounted for by an increase in synoptic wave activity in the region. The precipitation trend is related to a positive sea surface temperature trend in the nearby Atlantic Ocean, but apparently not causally. The trend in the Atlantic seems to result from a decrease in mechanical stirri...

Extreme discharge events in the Paraná River and their climate forcing

The largest discharge anomalies of the ParanaRiver were examined focusing on the contribution from the sub-basins and on the climate forcing of these events. Major discharge anomalies at Corrientes originated in the central and southern Upper Parana ´ basin with relatively small contributions from the Paraguay river and the northern Upper Paranabasin. About two thirds of the major discharge anomalies in Corrientes occurred during El Nino events while none was registered during La Nina events. Major discharge anomalies related to El Nino occurred either in the spring of the year of El Nino onset or in autumn of the following year (autumn (þ )) accompanying the precipitation signal of El Nino in eastern subtropical South America. The signal during autumn (þ ) is the most relevant as five out the six top discharges of the ParanaRiver at Corrientes occurred in this season. The remaining third of the major discharges not related to El Nino took place during the austral spring or austral summer of neutral periods. In each of these seasons, they share a common sea surface temperature anomaly pattern in the proximity of the South American coasts. q 2003 Elsevier Science B.V. All rights reserved.

On the Urban Heat Island Effect Dependence on Temperature Trends

For U.S., Argentine and Australian cities, yearly mean urban to rural temperature differences (ΔTu-r) and rural temperatures (Tr) are negatively correlated in almost every case, suggesting that urban heat island intensity depends, among other parameters on the temperature itself. This negative correlation is related to the fact that interannual variability of temperature is generally lower in urban environments than in rural areas. This seems to hold true at low frequencies leading to opposite trends in the two variables. Hence, urban stations are prone to have lower trends in absolute value than rural ones. Therefore, regional data sets including records from urban locations, in addition to urban growth bias may have a second type of urban bias associated with temperature trends. A bulk estimate of this second urban bias trend for the contiguous United States during 1901–1984 indicates that it could be of the same order as the urban growth bias and of opposite sign. If these results could be extended to global data, it could be expected that the spurious influence of urban growth on global temperature trends during warming periods will be offset by the diminishing of the urban heat island intensity.

The Paraná River Response to El Niño 1982–83 and 1997–98 Events

Abstract The most severe flooding of the twentieth century in the Argentine section of the Parana River occurred during the strong El Nino (EN) event of 1983. During the 1997–98 EN episode, discharge anomalies in the Parana basin, although of the same sign as those of the 1982–83 event, were much smaller. The main differences were observed during January–March and June–July of the year following the starting date of the event, when the 1982–83 discharge anomalies were considerably larger. This study explores this issue as well as the relationship between convection anomalies in the Parana basin and tropical Pacific and South Atlantic sea surface temperature (SST) anomalies. The correlation between convection in the upper and middle Parana and Iguazu basins, as measured by outgoing longwave radiation, and SST in both the Nino-1+2 and Nino-3 regions is statistically significant for most of the period November–July, reaching the maximum value in the three basins during May. However, the analysis of the highe...

Seasonal-to-Decadal Predictability and Prediction of South American Climate

Abstract The dynamical basis for seasonal to decadal climate predictions and predictability over South America is reviewed. It is shown that, while global tropical SSTs affect both predictability and predictions over South America, the current lack of SST predictability over the tropical Atlantic represents a limiting factor to seasonal climate predictions over some parts of the continent. The model’s skill varies with the continental region: the highest skill is found in the “Nordeste” region and the lowest skill over southeastern Brazil. It is also suggested that current two-tier approaches to predict seasonal climate variations might represent a major limitation to forecast coupled ocean–atmosphere phenomena like the South Atlantic convergence zone. Also discussed are the possible effects of global climate change on regional predictability of seasonal climate.

Identification of the principal patterns of summer moisture transport in South America and their representation by WCRP/CMIP3 global climate models

The goal of this study is to assess the ability of a set of global climate models (GCMs) to represent the main regional spatial patterns of austral summer moisture transport in South America in order to evaluate if one of the possible causes of GCMs misestimating summer precipitation in this region could be associated with an erroneous representation of these patterns. For this purpose, NCEP/NCAR reanalysis and 20 GCMs from the WCRP/CMIP3 multi-model dataset for the period 1960–1999 were considered. Extreme cases of moisture transport patterns were selected to assess their association with rainfall anomalies. Results obtained indicate that only some aspects of water vapor transport and convergence in South America as well as the associated precipitation anomalies can be reproduced adequately by GCMs. Finally, a case study is presented showing that one of the moisture transport patterns identified was observed during December 2008–February 2009.

Assessment of climate change on the future water levels of the Iberá wetlands, Argentina, during the twenty-first century

The Iberá wetlands, located in La Plata Basin, is a fragile ecosystem habitat of several species of flora and fauna and it also constitutes one of the largest inland freshwater of the world. In this study, the hydroclimatologic response to projected climatic changes in the Iberá wetlands is assessed. Bias corrected temperature and precipitation data from four Regional Climate Models (RCMs) developed for the CLARIS-LPB project were used to drive the calibrated variable infiltration capacity (VIC) hydrological model for different time slices. Derived future scenarios consist on changes in temperature, precipitation and water level of the Iberá Lake for the periods 2021–2040 and 2071–2090 with respect to present. All RCMs are consistent in predicting a warming for the near future (0–2°C) and also to the end of the century (1.5–4.5°C) in the study region, but differ in the sign and percentage of precipitation changes. VIC modelling results suggest that the Iberá Lake level could increase in the twenty-first century and that this increment would be higher in the summer months. Nevertheless, the projected 10 cm of water-level increase could be not so relevant as it is of the same order of magnitude than the observed interdecadal variability of the system.

Development of statistically unbiased twenty-first century hydrology scenarios over La Plata Basin

Abstract There is an increasing demand for future climate scenarios, particularly for impact studies. In this study, simulation outputs taken from a set of three regional climate models (RCMs) are used to force a hydrologic model to derive future streamflow scenarios for La Plata Basin. As RCMs have biases in their mean precipitation and temperature fields, a statistical scheme is previously used to remove the systematic part of the bias. Future hydrologic scenarios were derived considering two future periods: 2021–2040 (near future) and 2071–2090 (far future). In terms of climate projections, RCMs predict warmer conditions in almost the whole basin, while precipitation variations are not uniform in sign across the region but overall tend to be positive over the southern part of the basin. Nevertheless, a trend towards a gradual increase in streamflow was found for the majority of the rivers in the basin particularly for the near future followed by less uniform variations towards the end of the present century. Future changes in the largest monthly streamflow are similar to those in the mean values, with also some differences among RCMs and on the period and sub-basin considered.

Buenos Aires urban meteorological data analysis of a five-day period

Abstract Thermal humidity and airflow fields over the metropolitan area of Buenos Aires city (Argentina), for the period June 9–13, 1978, at 08:00, 14:00 and 20:00 AST have been analysed. This period was selected because of its little cloudiness ( The effect of the urban heat island and the influence of the greater water temperature appear in the thermal fields at 08:00 and 20:00. At 14:00 the opposite effect can be appreciated. The airflow fields at 14:00 show a rotation of the wind from north to south, through the east, during the period. At 08:00 and 20:00 there is no wind in the area. The mixing-layer height was also studied. This height was estimated using the upper air observations obtained from radiosonde ascents from Ezeiza Airport station and the daily maximum temperatures of the meteorological stations selected. In general, the fields of mixing height are similar to the thermal fields at 14:00, with urban values lower than suburban ones.