IWRA Proceedings

Abstract The Amancay project, grouping together French and South American scientific teams, has been starting four years ago. This project aims at understanding the climate varibility in tropical and subtropical South America from the seasonal to the decennal timescale. Specifically, it focuses on deciphering trend from abrupt changes and on comparing the different climate modes. Indeed, documentation of our climate for the recent period (the last centuries) is needed to separate the natural from the anthropogenic component. Main questions recovered by the Amancay project are: what is the local and the regional variability ? What are the teleconnexions between tropical and subtropical areas for the regional climate variability ? To answer those questions, four regions impacted by the South American Monsoon have been studied : the Nordeste, the South of the Amazon basin, the Andes and the Parana-Plata basin. We also focus on two specific time periods: the abrupt climate change in 1970 and the Little Ice Age (LIA). Our approach combines (1) documentation from past climate archives (corals, lake sediments and ice cores), (2) calibration of proxies to better interpret the climate archives using both modern observations and modelisation, and (3) climate and hydrology modelisations with a hierarchy of models. The main results that we present here are: (1) the abrupt feature in 1970 is a widespread event leading to a common moisturing of the tropical and subtropical South America and (2) the LIA is significantly recorded both in the Andean and the Parana basin climate archives but with different signatures: moist and cold conditions are shown in the Andes whereas lake sediments exhibit dry conditions in the Parana basin. For both periods, we seek to understand the mechanisms that can explain either local or common variations. For the later, the objective is to explore which kind of teleconnexions occured both between our key regions in South America and with other regions (specifically, with the Pacific and Atlantic Oceans).