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Characterisation of hydrological droughts in central-north Argentina and its atmospheric and oceanic drivers

Juan I. Caragunis*, Juan A. Rivera, Olga C. Penalba

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ABSTRACT: Low streamflows produce impacts on ecosystems and societies, especially on large timescales, caused by natural and anthropogenic forcings. The main basins, located in central-north Argentina (CNA), were analysed using centennial streamflow data. This study is focused on describing spatial and temporal variability of hydrological drought events, and evaluating the atmospheric and oceanic drivers under hydrological droughts conditions. The Standardized Streamflow Index in the period 1919–2014 was applied, sectored by four major basins. The western Argentinean Rivers (Colorado Basin, CB) show increasing drought events since the 1940 decade while on the east a sharp decrease occurs from 1970 onwards. The extreme drought events occurred over CB and La Plata Basin (LPB) during the periods 1966-1972 and 2010–2014. The atmospheric and oceanic patterns under hydrological drought conditions show anticyclonic anomalies over South Pacific Ocean (SPO), cyclonic sub-polar anomalies and La Niña-like conditions with warm Sea Surface Temperature Anomalies (SSTA) in SPO for the western basins. Over LPB, a strong cold SSTA on tropical south-western Atlantic Ocean is spotted and positioned on phase with the cyclonic anomalies. On mid-latitudes, a warm SSTA and anticyclonic anomalies are detected. Water vapour transport composites show southerly winds and drier conditions for north and east Argentina, and weakening of westerly winds with drier atmosphere for western rivers. The implications of these results will improve in a deepening in the knowledge of natural forcings to hydrological drought events in CNA and in the predictability of such complex hazard.