Precipitation and river discharge in subtropical South America: a long-term perspective from tree rings

FERRERO, M.E.; VILLALBA, R.; DE MEMBIELA, M.

Valdivia

Simposio; II International Symposium: Reconstructing climate variations in South America and the Antarctic Peninsula over the last 200 years; 2010

CIN, UACh - Facultad de Ciencias Forestales y Recursos Naturales

The sustainable management of water resources is an increasingly demanding topic in view of future climatic and human water-consumption projections. The disruption of the northeasterly humid-air flow by the Sub-Andean mountain ranges generates a latitudinal-band of enhanced orographic precipitation in subtropical northwestern Argentina (SNWA). These Sub-Andean mountain areas are the major sources of water for the river systems in NWA. It has been shown that tree-ring variations from the montane forests in SNWA are sensitive to annual or even seasonal variations in precipitation. Consequently, they provide a unique opportunity to evaluate the long-term variability in precipitation and streamflow across the region. Principal component analysis was applied to a network of Juglans australis chronologies in SNWA to determine the common patterns of variance among records. Correlation and multiple regression techniques were used to determine the relationships between the tree-ring dominant patterns and monthly rainfall variations. Based on the strongest correlations between precipitation and tree growth, transfer functions were developed to estimate past variations in precipitation during the past 2-3 centuries using tree-ring records as predictors. Our results indicate that variations in growth are related to late spring-summer rainfalls, the season of the year recording the largest precipitation, and consequently, the maximum runoffs in SNWA. According to our reconstructions, precipitation variability has increased since early 1990s leading to years of extremely-wet followed by very-dry events. Reconstructions of seasonal precipitation and streamflow may provide an important framework to evaluate the current hydroclimatic changes in the subtropical regions in South America influenced by the summer monsoon system.