Precipitation variability at sub-seasonal scale under the ENSO influence in southeastern South America

Abstract

El Niño–Southern Oscillation (ENSO) modules precipitation variability at seasonal and monthly scale over Southeastern South America (SESA), but also has incidence on how daily precipitation is distributed throughout the month. While most of the studies addressed the precipitation response at seasonal scale, the community research is advancing on the understanding of teleconnections at a finer scale. The objective of this study is to assess ENSO signal on the intensity and length of individual precipitation events at sub-seasonal scale during October-February for the period 1979–2015 over SESA. The distribution of precipitation was characterized through wet spells (WS): number and intensity for each month (NWS and IntWS, respectively). In the study region, short WS (1 day length) are more frequent over Uruguay and the southern part of Argentina whereas medium WS (2–6 days length) dominates in the center of the region. Both short and medium WS present higher intensity over central SESA. The ENSO signal is stronger during November over the centerof the study region and during December over Uruguay, and weakens the following months. Both hot spots during these months consist on higher monthly precipitation characterized by longer and more intense WS under El Niño phase, at the expense of lower occurrence of individual (1 day) rainfall events. Regarding inter-event variability, El Niño composite is more representative of strong events whereas mostly La Niña events presented negative anomalies with variable spatial pattern. This research is a contribution to answer to user demands for action planning to reduce climatic risk.