Marcela Hebe González

The relationship between tropical convection in South America and the end of the dry period in subtropical Argentina

The connection between the tropical convection over South America and rainfall in subtropical Argentina is studied using outgoing longwave radiation (OLR) measurements obtained from the scanning radiometer aboard the polar orbiting NOM operational satellites and rainfall measurements of 32 selected Argentine stations for the period 1975–1991. The mean annual rainfall cycle in subtropical Argentina can be described by the composition of the first three eigenvectors. The first eigenvector explains 59% of the variance having a strong influence in north-eastern Argentina and little variability during the year. The second, explaining 19% of the variance, represents the summer rainfall with maximum variability in the northwest part of the country. The third eigenvector explains 4% of the variance and is related to the semiannual cycle observed in the southeast of subtropical Argentina. The tropical convection may be related to rainfall in subtropical Argentina. It influences the vertical movements by compensatory subsidence and the higher humidity at low levels accompanying the convection, which can be advected towards Argentina. Also, the position of the mean centres of tropical convection is related to the latitude of the subtropical jet and of the tropospheric circulation. As a consequence, it influences the possible advection of humidity from the Atlantic Ocean. Different parameters are used to detect the influence of the onset of the summer monsoon on the end of the dry winter over almost all subtropical Argentina. Significant correlation is evident when rainfall in September in subtropical Argentina is correlated with the onset monsoon date anomaly. When the convection is advanced (delayed) from the climatic value, there are positive (negative) rainfall anomalies in the south-eastern region of subtropical Argentina.

Rainfall trends, land use change and adaptation in the Chaco salteño region of Argentina

Abstract Regional change under agricultural expansion in the Chaco of Argentina is determined by interactions of rainfall change, infrastructure development, socio-economic actions and values, and the social perceptions of change. Our study focused on adaptation in the socio-environmental system which is the key to understanding opportunities, uncertainties and risk in the context of historical change. Change in land use from extensive grazing through mixed farming and on to industrial-scale soybean production was made possible by a trend of increasing rainfall that reduced the risk of crop failure from drought since the 1970s. Rainfall change coincided with a period in which the Chaco forest was suffering extensive degradation from long-term extractive use. The degradation aided agricultural expansion since the degraded state of the ecosystem justified public policies of deforestation. In parallel to these resource-based processes, public policy changed in the late 70s and 80s toward favoring privatization of state land and exclusion of small producers. This permitted the land concentration needed for industrial-scale production. Technological innovation in both water and land resource management reinforced the process of concentration because small producers rarely have the financial or educational capital to develop or implement emerging technologies. One of the results of the intensification and expansion of agriculture is that soil surface sealing, waterlogging and flood risk are now effective at a landscape scale. To address these risks, private enterprise and government efforts must now come together toward innovative policies in integrated landscape management.

Some Factors That Influence Seasonal Precipitation in Argentinean Chaco

The Chaco plain region in Argentina is located in the north of the country and east of Los Andes where the main activity is the agriculture. As such activity is highly affected by interannual rainfall variability, the influence of some of the principal atmospheric and oceanic forcing is investigated in this paper. Results show that the factors which affect precipitation highly depend on the season and the subregion. The position of the South Atlantic Height and the sea surface temperature in the coast of southern Brazil and Buenos Aires seem to be the factors that affect rainfall, all over the year. The El Nino-Southern Oscillation phenomenon affects summer and spring rainfall and the Southern Annular Mode involves spring precipitation but both only in the east of the study region. Furthermore, enhanced convection in Central Brazil, mainly influences autumn and spring rainfall.