Representation of extreme El Niño events and associated atmospheric moisture flux convergence patterns in observations and CMIP6 global climate models

Extreme precipitation in the western tropical Andes have significant socio-economic impacts in northern Peru and Ecuador. Previous investigations have shown that high impact episodes were caused by atmospheric moisture flux convergence associated with strong El Niño events in the eastern Pacific Ocean, identifying two patterns: the one emerging during the 1982/1983 and 1997/1998 events, and the one emerging during the 2015/2016 event.

In this contribution, we discuss the ability of CMIP6 global climate models to represent these two types of extreme El Niño events, by analyzing the associated atmospheric moisture transport patterns. Based on SST observations, we identified historical extreme El Niño events using the relative Niño34 index, an index recently proposed for addressing ENSO in a warming climate. We also use ERA5 to compare with the moisture flux of CMIP6. We compared 13 CMIP6 models with the historical record (1901-2014). We found the following: (1) six of the models simulated the two extremes El Niño patterns; (2) 62% of the models identify 4.5 extreme El Niño events; and (3) only 27% of the models represent the seasonality of the moisture flux convergence overestimating the moisture flux convergence branch located to the south (4° S) of its normal position (4° N).

Our results provide a starting point to investigate the impacts of climate change and its impacts on atmospheric dynamics and associated extreme events at the regional level in tropical South America.