The Diverse Impacts of El Niño and La Niña Events over the South Pacific and in French Polynesia

Abstract El Niño–Southern Oscillation (ENSO) is the primary driver of global climate interannual variability, with El Niño and La Niña events disrupting atmospheric and oceanic conditions worldwide. These events form an “ENSO continuum,” from central Pacific to eastern Pacific events, each leading to different impacts. Understanding the diversity of these impacts is crucial for the vast but understudied south-central Pacific and French Polynesia (FP). Here, we use a multivariate cluster classification approach on relative sea surface temperature (RSST), precipitation, and zonal wind, combined with an atmospheric model ensemble forced by observed sea surface temperature (SST). We show that ENSO intensity and spatial pattern diversity are the main drivers of FP interannual climate variability. With opposite SST/air temperature anomalies between northeastern and southwestern FP, FP has a pivotal position. Precipitation anomalies are highly dependent on ENSO strength and spatial pattern and are primarily driven by anomalous convergence of large-scale climatological moisture. Notably, the extreme eastern Pacific El Niño events of 1982/83 and 1997/98 caused severe precipitation in northeastern FP, while the strong mixed (central-eastern Pacific) 2015/16 El Niño had a different South Pacific convergence zone position and more moderate precipitation over northeastern FP. The 2010/11 and 2021/22 multiyear La Niña events form their own cluster and stand out with significant drying over the south-central Pacific. We also use these clustering results to evaluate and discuss the effectiveness of existing indices in describing ENSO impacts over FP.