Reconstructing hydroclimatic variability in the South Southern Andes from Documentary Sources. 17th to 20th centuries.

PRIETO, M.ROSARIO; CUETO, CLARA

Bern

Congreso; XVIII INQUA-Congress; 2011

International Union for Quaternary Research -Bern University

Abstract Archival documents have been used to reconstruct the hydroclimatic variability occurring in the high basin of the Bermejo River (Argentina-Bolivia) during the last centuries as well as its effects on the droughts, floods and swellings in the middle basin. Administrative documents from the Hispanic-American colonial and republican periods have provided useful information to reconstruct the climate and the hydrology of the region. Documents from the Archivo General de Indias in Seville, Archivo Nacional de Bolivia, and Archivo General de la Nación (Argentina) have been used to identify extreme events in the high and middle-basin of the Rio Bermejo from the 17 th century to the first decades of the 20 th century. Old maps of the region were also used. The archival documents show abrupt hydrological changes in response to the climatic fluctuations in the headwaters region. More than 20 distinct floods, low water periods and droughts have been identified between 1800 and 2000. There is also historical evidence suggesting that flood events have increased in frequency and intensity during the last century. Analyses of instrumental records from the 20th century show contrasting trends in discharge from rivers located north and south of the South American “Arid Diagonal”. During the 20th century streamflow for basins north of the “Arid Diagonal” have increased whereas those to the south of it have decreased. In this case, the positive trend from the Bermejo River contrasts with the negative trend and the increased variability of the hydrological cycle of the Mendoza River in the Central Andes. To corroborate the differences between both north and south river streamflows, the historical reconstruction of the Mendoza River streamflow from 18th century (Neukom et al 2009) was correlated with the reconstruction of the Bermejo River streamflow. According to the results, it is possible to speculate that, due to warming, the contribution of the Atlantic moisture over the continent has increased at subtropical latitudes during the 20 th century, whereas the Pacific input has decreased at middle and high latitudes.