Precipitation response to El Niño/La Niña events in Southern South America ndash; emphasis in regional drought occurrences

摘要

The ENSO phenomenon is one of the key factors that influence the interannualvariability of precipitation over Southern South America. The aim of thisstudy is to identify the regional response of precipitation to ElNiño/La Niña events, with emphasis in drought conditions. Thestandardized precipitation index (SPI) was used to characterizeprecipitation variabilities through the 1961–2008 period for time scales of3 (SPI3) and 12 (SPI12) months. A regionalization based on rotated principalcomponent analysis allowed to identify seven coherent regions for each ofthe time scales considered. In order to identify the regional influence ofEl Niño and La Niña events on the SPI time series, we calculated themean SPI values for the El Niño and La Niña years and assessed itssignificance through bootstrap analysis. We found coherent and significantSPI responses to ENSO phases in most of the seven regions considered, mainlyfor the SPI12 time series. The precipitation response to La Niña eventsis characterized with regional deficits, identified with negative values ofthe SPI during the end of La Niña year and the year after. During ElNiño events the precipitation response is reversed and moreintense/consistent than in the case of La Niña events. This signal hassome regional differences regarding its magnitude and timing, and thequantification of these features, together with the assessment of the SSTcomposites during drought conditions provided critical baseline informationfor the agricultural and water resources sectors.