Changes on the summer Rx1-ENSO and Rx1-SAM relations over Northern Argentina driven by PDO phases

Abstract

This study examines the variability of summer maximum daily rainfall (Rx1) in Northern Argentina (NA) and its relationship with the El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM). Also, it analyzes the role of the Pacific Decadal Oscillation (PDO) in modulating these relationships. The analysis includes 28 daily rainfall records from different weather stations spanning at least 50 years (1969–2019). Rx1 is a relevant metric for daily rainfall intensity linked to flood events, yet no previous studies have explored this topic in the region. Due to the lack of significant correlations over the entire period, a methodology was adopted to identify the period of minimum p-value (PmPV) in the correlation coefficient (RHO) to highlight sub-periods where relationships between Rx1 and ENSO/SAM were stronger. The results reveal that PDO influences PmPV, spatial RHO distribution, and atmospheric patterns of ENSO and SAM. During PDO’s negative phase (PDO-), ENSO effects become widespread in NA, with Rx1 increasing under positive ENSO phases and decreasing under negative phases in most stations. On the contrary, in PDO’s positive phase (PDO+), ENSO’s impact is more restricted to the eastern region. For SAM, RHO values show mixed signs, without a consistent pattern between PDO- periods. Shifts in PDO phases affect typical ENSO and SAM circulation patterns, altering northern moisture transport and Rx1 values. This research highlights a non-stationary influence of global variability on extreme precipitation.