Unprecedented Rainfall and Moisture Patterns during El Niño 2016 in the Eastern Pacific and Tropical Andes: Northern Perú and Ecuador

Abstract

Using vertically integrated water vapor and its convergence, associated with large-scale and regional atmospheric circulation, we found two patterns of rainfall over the Eastern Pacific (EP) and the tropical Andes-with a focus in Ecuador and northern Perú-during three recent El Niño events: 1983, 1998, and 2016. Although these three events were the strongest El Niños, the different sources of moisture contribute to different rainfall patterns between El Niño 1983–1998 and 2016. In the region, the spatial pattern of precipitation during El Niño 2016 presents an unprecedented out-of-phase atmospheric response consistent and verified with water vapor transport when compared with El Niño 1983–1998. During El Niño 2016, precipitation in the Andes was enhanced by moist air transported from the Amazon—with an opposite regime compared to the subsidence that dominated in 1983–1998. During the 1983–1998 El Niño, the source of moisture to feed the EP was enhanced by upper-level divergence (300 hPa), which supports moisture influx by middle levels in the EP. In El Niño 2016, this divergent upper-level flow migrated north, followed by the companion moisture. This study illustrates a link between upper-level large-scale circulation and low-level regional mechanisms on the moisture transport in determining different rainfall patterns during El Niño events.