2019/2020 drought impacts on South America and atmospheric and oceanic influences

Abstract

The 2019/2020 drought in South America caused many impacts on several sectors, as agriculture, water resources and environment, which are reported here. Besides, there is a discussion about anomalies in the atmosphere and ocean during the analyzed period. In a regional scale, there was a reduction of humidity flux over the continent, and in a large scale, the occurrence of different processes could have contributed to the dry conditions. There was a persistent pattern of west-east convection anomalies in the tropical Pacific that could be related to the steady conditions observed over South America and southeast South Atlantic from September 2019 to March 2020. The extreme positive phase of the Indian Ocean Dipole during 2019 austral spring was another event that could have influenced temperature and precipitation in South America through a wavetrain from the Indian Ocean to the South American continent. The Sudden Stratospheric Warming that occurred in September 2019 induced the negative phase of the Southern Annular Mode in December, which generated subsidence over the subtropics and affected the precipitation over South America. In addition, from September 2019 to March 2020, the heating observed in the stratosphere propagated to the troposphere over South America. Ocean indices from 1982 to 2020 are analyzed in the context of dry conditions in the continent and it was observed the relations with AMO, PDO, IOD and El Niño 3.4. From September 2019 to March 2020, there were positive SST anomalies in all oceans, mainly in the North Atlantic Ocean, which could have contributed also to subsidence over South America through a meridional circulation, as seen in other cases. At the end of the studied period, the development of La Niña extended the situation of reduced precipitation in Southern Brazil.