Analysis of Dry and Wet Episodes in Eastern South America during 1980-2018 Using SPEI

A large part of the population and the economic activities of South America are located in eastern continent (ESA). ESA is affected by the South American monsoon system, and most of the region belongs to the Amazon, Araguaia-Tocantins, and La Plata basins. The precipitation over ESA may be modulated by the moisture transported from the Atlantic Ocean, mainly the subtropical South Atlantic along the year, and particularly the tropical North portion during the Austral Summer. Extreme climate dry and wet episodes are a recurrent phenomenon in areas of ESA, with environmental and socio-economic impacts, and a quantitative assessment of occurrence of extreme climate events is essential for understanding, monitoring and mitigation of such episodes. This study aims to analyze the extreme climate events at domain-scale occurring over ESA over the last four decades through the multi-scalar Standardized Precipitation-Evapotranspiration Index (SPEI). Based on the results of a Lagrangian approach developed for moisture analysis, the study area consists in the major continental sink of the moisture transported from the Subtropical South Atlantic Ocean towards South America, comprising the Amazonia, almost all the Brazilian territory, and La Plata regions. The SPEI was calculated for the period 1980-2018 using monthly CRU (TS4.03) precipitation and potential evapotranspiration time series (at an original spatial resolution of 0.5 degrees) averaged over the study area. The extreme episodes affecting different components of the hydrological cycle were identified through the SPEI-1, SPEI-3, SPEI-6, and SPEI-12 time series, and their respective indicators (duration, severity, intensity, and peak) were then computed. Preliminary results indicate the predominance of dry episodes in the 2010 decade, while the wet ones prevailed in the middle of the 1990s. The role of the moisture transport from the South Atlantic on the occurrence of these extreme episodes will be investigated in a further study.