Characterisation of hydrological droughts in centralnorth Argentina and their atmospheric and oceanic drivers

Abstract

Low streamflows caused by natural and anthropogenic forcings affect ecosystems and societies, especially on large timescales. We analysed the main basins of central-north Argentina (CNA) using centennial streamflow data. This study is focussed on describing spatial and temporal variability of hydrological drought events, and evaluating the atmospheric and oceanic drivers under hydrological drought conditions. The Standardized Streamflow Index in the period 1919-2014 was applied, sectored by 4 major basins. The western Argentinian rivers (Colorado Basin, CB) have shown increasing drought events since the 1940 decade, while in the east, a sharp decrease occurred from 1970 onwards. Extreme drought events occurred over CB and La Plata Basin (LPB) during the periods 1966-1972 and 2010-2014. Atmospheric and oceanic patterns under hydrological drought conditions show anticyclonic anomalies over the South Pacific Ocean (SPO), cyclonic sub-polar anomalies and La Niña-like conditions with warm sea surface temperature anomalies (SSTAs) in SPO for the western basins. Over LPB, a strong cold SSTA in the tropical south-western Atlantic Ocean is positioned in phase with the cyclonic anomalies. At mid-latitudes, a warm SSTA and anticyclonic anomalies are detected. Water vapour transport composites show southerly winds and drier conditions for northern and eastern Argentina, and weakening of westerly winds with drier atmosphere for western rivers. These results deepen our knowledge of natural forcings related to hydrological drought events in CNA and in the predictability of such complex natural hazards.