Rainfall along the coast of Peru during strong El Niño events

Abstract

While, climatologically, most areas of the Peruvian Pacific region do not experience precipitation, they can be affected by heavy rain and flooding during strong El Niño events with severe socio-economic impacts. Only four strong El Niño events took place within the last five decades (1972/1973, 1982/1983,1997/1998 and 2015/2016) which led to significant rainfall events in the northern part of Peru. Here a detailed analysis of the evolution of precipitation during these events was performed using gauge records from 1964 to 2016 from a network of 145 meteorological stations located along the Peruvian Pacific region. Through empirical orthogonal function analysis, the rainfall anomalies variability is interpreted as resulting from the combination of a meridional see-saw mode (North–South) (Ep mode) and a zonal see-saw mode (East–West) (Cp mode) that represent, respectively, 34 and 21% of the explained variance. It is shown that the extreme 1982/1983 and 1997/1998 El Niño events have a dominant projection on the Ep mode that has a strong loading in the northern region, while the 1972/1973 and 2015/2016 El Niño events have a relatively weak projection onto the Ep mode (about ten times less at the peak rainy season than the extreme events) and mostly project onto the Cp mode. Also, it is shown that while all events are associated with positive rainfall anomalies in the northern part of Peru which is accounted for by the Ep mode, the evolution of rainfall anomalies along the Cp mode exhibits a significant dispersion. This suggests that the impact of strong El Niño events on the highlands along the coast cannot solely be inferred from the magnitude of the sea surface temperature anomalies in the central equatorial Pacific. Overall, our study illustrates the nonlinearity of the ENSO teleconnection on the rainfall along the coast of Peru during strong El Niño events.