The role of ENSO flavours and TNA on recent droughts over Amazon forests and the Northeast Brazil region

Abstract

Amazon tropical forests and the semiarid Northeast Brazil (NEB) region have registered very severe droughts during the last two decades, with a frequency that may have exceeded natural climate variability. Severe droughts impact the physiological response of Amazon forests, decreasing the availability to absorb atmospheric CO2, as well as biodiversity and increasing risk of fires. Droughts on this region also affect population by isolating them due to anomalous low river levels. Impacts of droughts over NEB region are related to water and energy security and subsistence agriculture. Most drought episodes over Amazonia and NEB are associated with El Niño (EN) events, anomalous warming over the Tropical North Atlantic (TNA), and even an overlapping among them. However, not all the dry episodes showed a large‐scale pattern linked to a canonical EN event or warm TNA episodes. For instance, dry episodes linked to EN events present distinct spatial patterns of precipitation anomalies depending on EN type (Central‐Pacific vs. Eastern‐Pacific EN), and NEB region experienced a severe drought in 2012 that is not attributed to EN or warm TNA events. Even in the case of the strong EN in 2015/16, some regional impacts have not been explained by EN contribution. This paper discusses the effects of CP and EP EN events, and the role of warm TNA events on tropical Walker and Hadley circulation leading to drought over Amazonia and NEB regions.

Rainfall extremes and drought in Northeast Brazil and its relationship with El Niño–Southern Oscillation

“…When related to the contributions of the years in this PC, we detected that 1967 stands out with 16.8% of the total variance, while Satuba is the main station, with 8.3% of the total variance. The presented pattern of negative PC Loadings to the extreme west and north of the State of Alagoas agrees with the findings obtained previously by Brito et al (2018) and Jimenez et al (2019), in the aspect of higher EN influence on these regions, in this case the Hinterland and Arid Zone mesoregion. Both studies also show a significant reduction in the occurrence of rainfall in the areas mentioned.…”

“…Both ENSO and GITSMA are essential factors that directly influence NEB rainfall dynamics (Hastenrath and Heller, 1977; Silva Costa et al, 2015). It is worth mentioning the several previous studies reporting the relationship between the SST of the Pacific and Atlantic Oceans related to NEB rainfall (Pezzi and Cavalcanti, 2001; Kayano and Andreoli, 2004; Kayano et al, 2013; Jimenez et al, 2019).…”

“…Marengo (2006) also observed reductions in rainfall in EN years, followed by an increase in LN years to the Northern and Northeastern of South America (SA) from 1979 to 2000. ENSO influences both North and South Atlantic (Giannini et al, 2004; Marengo et al, 2018; Jimenez et al, 2019). However, the ENSO influence on the Equatorial Atlantic is less observed (Marengo et al, 2018; Jimenez et al, 2019) and may occur in the opposite direction, as found here, where the action of EN favoured extreme rainfall.…”

“…There is a direct relationship between EN and droughts in NEB, where the anomalous change in the upper atmospheric circulation and, consequently, the change in the dynamics of the high and low‐pressure centres, followed by the modification of the atmospheric circulation cells (Marengo and Bernasconi, 2015), constitute mechanisms that explain the occurrence of prolonged droughts in NEB (Molion and Bernardo, 2002; Reboita et al, 2010). The EN events coincide with the more prolonged droughts in NEB, whose cycles alter the weather and climate conditions and, consequently, negatively affect the rainfall in the region (Marengo et al, 2018; Jimenez et al, 2019). It is worth noting that not always the EN (LN) years coincide with rainfall below (above) the expected average.…”

Attribution of Amazon floods to modes of climate variability: A review

“…East Pacific and central Pacific El Niños) and variable specific indices such as the OLR defined events. Such work has already begun for extreme precipitation events in South America (Tedeschi et al ., 2016), summer rainfall over Peru (Sulca et al ., 2018) and recent droughts in the Amazon basin (Jimenez et al ., 2019).…”