Australian Rainfall Projections Associated with ENSO Diversity in a Warming Climate: Insights from CMIP6 Large Ensembles

Abstract El Niño–Southern Oscillation (ENSO) is an important climate driver of rainfall variability in Australia. This study examines changes in Australian rainfall associated with four ENSO types: eastern Pacific (EP) and central Pacific (CP) types of both El Niño and La Niña, between the historical period (1945–2014) and the future period (2031–2100) under the shared socioeconomic pathway (SSP3-7.0) scenario using four large ensemble climate model simulations. These large ensembles project three potential future pathways in a warming climate: weaker, unchanged, and stronger ENSO events. Regardless of the pathway, models tend to project an increased frequency of El Niño events in the future, with a robust increase in CP El Niño occurrences. In contrast, La Niña frequency is expected to remain similar to historical levels. The impacts of CP and EP ENSO on Australian rainfall exhibit greater seasonal and model consistency during La Niña events than during El Niño events, both in the historical period and in future projections. The most significant CP and EP ENSO–related Australian rainfall changes are projected to occur between December and May. While the amplitude of rainfall changes associated with El Niño types varies depending on the future ENSO pathway, an overall increase in rainfall during La Niña events is consistently projected between December and May. Despite general agreement on the sign of La Niña rainfall projections, there is a considerable variation among ensemble members regarding the intensity of the rainfall increase. These findings underscore the value of using multiple climate models for more reliable rainfall projections, providing critical insights for climate adaptation strategies in Australia. Significance Statement El Niño–Southern Oscillation (ENSO) is a key climate phenomenon influencing global weather patterns in the tropics and extratropics, including Australia. This study explores how Australian rainfall could change with different ENSO types between the periods of 1945–2014 and 2031–2100 under climate change. The evaluated coupled climate models predict three possible future trends in a warming climate: weaker, unchanged, and stronger ENSO. No matter the trend, El Niño events are expected to become more frequent, while La Niña events will occur at similar rates as in the past. The most significant changes in rainfall are expected to happen between December and May. Although the amount of rainfall change linked to El Niño varies depending on the future ENSO pathway, there is a consistent projection of increased rainfall during La Niña events, especially between December and May.