ENSO's Impacts on Southeastern Australia's Future Rainfall Risk

Abstract The El Niño‐Southern Oscillation (ENSO) importantly influences Australian rainfall variability. In southeastern Australia, La Niña is observed to cause a larger risk of high rainfall than El Niño does for low rainfall, demonstrating a non‐linear ENSO‐rainfall relationship. In this study, we first assess the ENSO‐rainfall relationship for 10 single model initial‐condition large ensembles (LEs) over the Murray‐Darling Basin. We then apply a novel Fraction of Attributable Risk framework to quantify the projected rainfall risk in this region, specifically to the five LEs that have the same ENSO‐rainfall relationship as observations. Despite no prominent change in El Niño related rainfall amount or its variability, rainfall variability increases during La Niña and neutral phases. Additionally, three out of five LEs project an increase in rainfall risk during La Niña events, with both greater variability and higher amounts of rainfall, suggesting that the La Niña‐driven rainfall impacts may worsen under a warming climate.