ENSO and PDO related variability in seasonal range prediction for the Bolivian Altiplano region in South America

Abstract

This study uses the methodology of some experiences in seasonal range prediction related to El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) in North America. Previous studies (e.g Garreaud and Aceituno 2001; Vuille and Keimig 2004) in the Bolivian Altiplano focused on interannual variability of DJF precipitation as the EN (El Niño) phase was related to droughts, but the ENSO influence over the region is more complex. For this study monthly precipitation, maximum and minimum temperature from 1979 to 2015 are used to study how ENSO and PDO influence the climate conditions in the Bolivian Altiplano. A power spectra analysis confirmed the periodicities associated to ENSO and PDO. Further, an analysis of variance and the frequency distribution calculation per PDO and ENSO phase were applied using standardized anomalies. The differences between distributions were tested using Chi-squared goodness of fit. Our results suggest an influence of PDO over ENSO, displaying dry anomalies for DJF (Dec-Jan-Feb) in EN/PDO(+) in agreement with previous studies, and wet anomalies for SON (Sep-Oct-Nov) in NU (Neutral)/PDO(+). For maximum temperature, a reduction in cold anomalies during EN/PDO (-) along the year was observed with greater warm anomalies in JJA (Jun-Jul-Aug), SON, and MAM (Mar-Apr-May). Similar results were observed for PDO influence over the NU phase and minimum temperature results displayed more variation within the stations. Finally, an upper-level circulation analysis and changes in the jet stream were observed. Strengthened jet cores were observed in the current PDO and the coupling of two jet streaks enhances the convergence zone upstream of South America. These results would allow production of seasonal forecasts based on ENSO and PDO using upper-level information and surface meteorological information.