Intraseasonal Drivers of the 2018 Drought Over São Paulo, Brazil

Abstract

Dry conditions occurred over São Paulo state (southeastern Brazil) from February to July 2018, causing the driest semester in 35 years. Socioeconomic impacts included a record number of fire spots, most adverse conditions to pollutant dispersion in 3 years and the winter's lowest water reservoirs stored volume in 17 years. This paper discusses climate drivers to the onset and persistence of the dry conditions, with special attention to the intraseasonal forcing. Barotropic atmospheric circulations forced by the intraseasonal Pacific-South America teleconnection pattern, embedded in the lower frequency setup of the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation, were identified as main large-scale forcings to reduce precipitation. Drought evolution was modulated by other intraseasonal drivers such as the Madden Julian, Antarctic and 10–30 days Oscillations. A break in the 6-month dry condition, in March 2018, highlighted the important role of such oscillations in determining precipitation anomalies over SP. Results show that intraseasonal phenomena and their interactions control drought characteristics such as magnitude, persistence and spatial distribution within a setup determined by lower-frequency oscillations. The intraseasonal timescale seems to be key and must be considered for a complete description and understanding of the complex drought evolution process in São Paulo.

Atmospheric circulation patterns associated with surface air temperature variability trends between the Antarctic Peninsula and South America

“…In the South Atlantic, the high-pressure anomaly observed through the positive anomalies 500-hPa height and the 850-hPa anticyclonic circulation, suggest a strengthening of the south/southwest branch and/or a south/ southwest displacement of the South Atlantic Subtropical High (SASH). This anomalous configuration can prevent the normal passage of extratropical cyclones and frontal systems over the east coast of South America (Seth et al 2015, Coelho et al 2016, Gozzo et al 2022. This results in the suppression of convection in southern Brazil, Uruguay and northeastern Argentina.…”

“…Variations in the position of the SASH can contribute to precipitation anomalies and even hydrological extremes over Brazil. For example, the severe droughts of in southeastern Brazil and of 2018 in the state of São Paulo were associated with the westward shift of SASH, preventing the normal passage of transient systems and, thus, contributing to a weakening of SACZ events (Seth et al 2015, Coelho et al 2016, Gozzo et al 2022.…”

Assessment of Precipitation and Hydrological Droughts in South America through Statistically Downscaled CMIP6 Projections

“…Droughts are a natural phenomenon characterized by a continuous persistence of precipitation deficit, which occurs in almost all climate zones, including those with high precipitation rates, such as Amazonia [4]. Prolonged periods of drought cause innumerable damages, such as losses in agriculture and livestock, contamination of waters, reduction of water availability for daily consumption and water energy generation, and environmental risks of fires [5,6]. Due to climate change and increasing temperatures, droughts are expected to increase in frequency and duration [7,8].…”

“…The semi-arid Northeast of Brazil is one of the historically most vulnerable regions to droughts [26], with several events recorded since the 16th century [26][27][28] and numerous socioeconomic impacts, such as damage to agricultural production and livestock, as well as loss of human life from hunger, malnutrition, disease, migrations to urban centers, and losses in regional and national economies [27]. Southeastern Brazil (SEB) has also experienced some of the worst droughts in recent decades, such as in 2001 [29], 2014/2015 [30][31][32][33][34][35], 2018 [6], and most recently, in 2020/2021 [36].…”

“…However, as SPI does not account for the temperature component, its analysis disregards evapotranspiration processes, which play an essential role in the hydrological cycle [56,58]. Despite its limitations, several studies have employed the SPI-12 index (SPI index on a 12-month time scale) due to its simplicity of implementation to identify hydrological droughts in SA [6,56,58,[60][61][62][63][64][65][66].…”