Multiyear La Niña effects on the precipitation in South America

Abstract

The effect of multiyear La Niña (LN) events on precipitation in South America (SA) was assessed considering 10 persistent LN events over two successive years, referred to as Y1 and Y2 for the 1901-2012 period. Y1 spans from the austral winter of the first year to autumn of the second year, and Y2 spans from the austral winter of the second year to autumn of the third year. Comparisons were performed season by season of the Y1 and Y2. Composites revealed that the teleconnections related to a multiyear LN event during its Y1 and Y2 years, responsible for distinct seasonal precipitation anomaly patterns in SA, were associated with different tropical ocean conditions. In spring, the negative sea surface temperature (SST) dipole in the Indian Ocean during the Y2 was not observed during Y1. Different LN-related SST anomaly patterns in the tropical Atlantic between Y1 and Y2 occurred in the other seasons. Over northern/northeastern SA, the positive precipitation anomalies became weaker (stronger) during austral summer and autumn (winter and spring) of the Y2 than Y1 and were associated with changes in the Walker cells. During austral spring and summer, southeastern presented drier conditions during the Y2 than Y1. In the spring of Y2, two Rossby wave trains, one associated with the LN-related anomalous cooling in the equatorial Pacific and another triggered by the upper-level anticyclone in the tropical Indian Ocean, characterized the circulation pattern over SA which explains the difference in precipitation anomalies between the Y2 and Y1. These drier (wetter) conditions during austral spring and summer (winter and spring), particularly over southern and southeastern Brazil (Colombia) in the Y2, might have more severe effects on the regional hydrological cycle than those in the Y1. The results here indicate that accurate prediction of LN duration is crucial in a climate-monitoring context.

Multiscale Interactions of Climate Variability and Rainfall in the Sogamoso River Basin: Implications for the 1998–2000 and 2010–2012 Multiyear La Niña Events

“…Nevertheless, SPI6 smooths the series and has fewer fluctuations (Figure 3c), and SPI6 allows for typification of common events for most stations, such as the wet periods of 1988-1989, 1995-1996, 1998-2000, 2010-2012, 2016-2017, and 2017-2018, and the dry periods of 1991-1992, 1997-1998, 2002-2003, 2009-2010, and 2014-2016; these periods are in agreement with those classified by NOAA as La Niña and El Niño events, respectively. An important feature noticeable in the PC1 of SPI3 and SPI6 (Figure 3b,c) is the persistence of some anomalous rainfall events in the SRB for more than two years, consistent with current reports of multiyear ENSO events [7,19,72,73]. In this regard, a rainfall deficit in the SRB is observed from 2014 to 2016, coincident with the multiyear 2014-2016 El Niño event.…”

“…Moreover, the PC1 also shows two persistent excess rainfall events: a first event between 1998 and 2000 and a second event between 2010 and 2012, which coincide with the multiyear La Niña events discussed by Iwakiri and Watanabe [18] and Lopes et al [7]. An important feature of these events is that they were immediately preceded by El Niño events-in this case, the 1997-1998 and 2009-2010 periods, respectively, consistent with [18,75,76].…”

“…It is widely recognized that a large set of extreme hydrological and meteorological events around the world are triggered by the El Niño-Southern Oscillation (ENSO) phenomenon, considered the most important modulator of global hydroclimatology at interannual time scales [4]. ENSO has two phases, which are the result of atmosphere-ocean interactions reflected by sea surface temperature (SST) conditions in the tropical Pacific basin [5,6], where the SST is higher (lower) than the climatological average during an El Niño (La Niña) event [4,7]. According to Aceituno et al [8] and Cai et al [6], in South America, the two phases, El Niño and La Niña, influence the hydroclimatology of the Andean region, recognizing ENSO as the most important source of interannual variability in northern South America; El Niño (La Niña) is linked with below (above)-average precipitation, soil moisture, and river discharges [9].…”

“…In the last forty years, the El Niño (La Niña) events recorded during 1997-1998 and 2015-2016 (1998-2000 and 2010-2012) stand out as the strongest events, with significant negative consequences for the country [6,9,11,[15][16][17], mainly during La Niña events, which were of longer duration than El Niño events. According to Iwakiri et al [18], this behavior is due to the strong transition asymmetry of ENSO, whereby El Niño concludes quickly, whereas some La Niña events often last more than two years and are defined as multiyear events [7,18,19]. The persistence of multiyear El Niño and La Niña events exacerbate the induced climate impacts, generating persistent floods and droughts worldwide [9,[20][21][22][23].…”

“…In this sense, relevant advances in the comprehension of Colombian climate have been made in studies addressing the influence of the ENSO phenomenon on hydroclimatology at different time scales [9,17,[37][38][39]. In particular, ENSO events such as the 2010-2012 La Niña were investigated by Arias et al [9] and Lopes et al [7]; however, they did not examine the multiscale interactions of climate variability and rainfall or the relationships between the length and intensity of the multiyear La Niña events. Therefore, in this study, we address the following questions: (i) Which have been the events of excess or deficit of precipitation in the SRB, and which are the main patterns of variability?…”