Abstract
ABSTRACT The 2020 drought in southern Brazil, which culminated in late summer and early autumn (February-March-April), displayed one of the most deficient rainfall totals in such trimester. This period of the year has already been dominated by negative rainfall deviations since the end of the 1990s. This recent drought represents, therefore, a significant worsening in an already unfavorable situation of water availability. Such long-term behavior is due to the combination of opposite phases of two interdecadal oscillations in the sea surface temperature: the positive phase of the Atlantic Multidecadal Oscillation and the negative phase of the Pacific Interdecadal Oscillation. This combination produces variation in the atmospheric basic state that favors less rainfall in southern Brazil at this time of the year and more frequent occurrence of droughts. For an extreme event to occur, it is usually necessary that, in addition to interdecadal oscillations, an interannual oscillation event occurs that also favors drought, such as the events of Central El Niño in 2020 and La Niña in 2009 and 2012, years of droughts in southern Brazil during the same phase combination of the two interdecadal oscillations. Anthropic climate changes can intensify the frequency and intensity of these extreme events.
Highlights
The 2020 drought and its impactsThe trimester February-March-April (FMA) 2020 was a very dry period in southern Brazil, preceded by some dry months in the previous year, especially in late austral winter and early spring
sea surface temperature (SST) anomalies occurred in regions connected with the climate oscillations Central El Niño (CEN), Atlantic Multidecadal Oscillation (AMO) and Interdecadal Pacific Oscillation (IPO) (Figure 1, upper right panel)
Within the interdecadal context of an atmospheric basic state more favorable or unfavorable to precipitation in a certain region, the occurrence of interannual or intraseasonal time scale climate events that produce effects in the same direction as the interdecadal oscillations, may lead to extreme events of rainfall or drought
Summary
The trimester February-March-April (FMA) 2020 was a very dry period in southern Brazil, preceded by some dry months in the previous year, especially in late austral winter and early spring. It was one of the worst ever droughts in the region, which affected several sectors, such as agriculture, hydropower generation and water supply to the population. The problem was first observed through monitoring made by the hydropower sector, as monthly natural inflows to the Subsystem South were below 70% of long-term averages since July 2019, despite a mild recovery in November of that year (Operador Nacional do Sistema Elétrico, 2020a). Electricity supply in Brazil depends on the National Interconnected System (SIN), which comprises four subsystems, with Subsystem South encompassing the three above-mentioned southern states
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