flow changes in Southern South America during the 20th century

PASQUINI, A. I., DEPETRIS, P. J.

Laguna Mar Chiquita, Córdoba, Argentina

Congreso; Third Joint Meeting. Holocene environmental catastrophes in South America: from the lowlands to the Andes.; 2005

CIGeS, UNC, Argentina- ICSU DARK NATURE – IGBP 490

During the last decade, several authors have identified various mechanisms that control anomalous climate in southern South America. Rainfall and river flow often show connections with the ENSO-triggered 2-6 year interannual spectral peak, with the near-decadal signal determined in the Atlantic and the monsoonal influence associated with the low-level jet circulation pattern (e.g. Robertson and Mechoso, 1998). In this paper we revisit the occurrence of anomalous flow in the Río de la Plata drainage basin and also –with the use of annual and seasonal Mann-Kendall tests- the significance of increased discharge. Such methodology was also implemented for the examination of river flow in the Patagonia region. The results show that most Río de la Plata gage stations exhibit a clear connection with the ENSO as well as a clear near-decadal signature. Moreover, in the Paraná River, discharge has increased significantly (p<0.01) during the last 30 years, particularly during the months of low discharge (Aug.- Nov.). Similarly, the Paraguay and Uruguay Rivers exhibit a significant discharge increase during the low flow months. In Patagonia, the signal of ENSO is somewhat faint but discernible in most rivers (e.g. in the Santa Cruz River, Depetris and Pasquini, 2000). Most Patagonian rivers exhibit a negative trend in their flows series, although only one of such yearly signals –the Negro River- is significant (p<0.01). Other rivers show a significant negative trend (p<0.05) in their seasonal discharge (e.g. the Chubut River during summer). The Santa Cruz is the only Patagonian river showing a significant increasing trend in the Sept.- Dic. period, probably due to ice and snowmelt determined by climate change.