Picture: Lake Hume, Victoria. Credit: Tim Keegan (Flickr Creative Commons – CC BY-NC 2.0)

El Niño Southern Oscillation (ENSO) events are extremely important for many countries around the world due to their impacts on rainfall.

By separating El Niño into central Pacific and eastern Pacific events, we show that the strength of a central Pacific event controls the rainfall amount for southeastern Australia. The stronger a central Pacific event is, the drier it is over Australia during the onset phase from April to September. But after October during the mature phase of El Niño, the strongest central Pacific events lead to more rainfall than normal over the southeast Australian river catchment known as the Murray Darling Basin, whereas the weakest central Pacific events lead to less rainfall than normal. This relationship is strongest in January to March around the time that the central Pacific event is fully developed.

For the strongest central Pacific events, this can be explained by a change in the circulation from drier, more westerly flow during the onset phase to moister, more easterly onshore flow during the mature phase. This finding is important for agricultural and water resources planning efforts in the Murray Darling Basin region and may help with seasonal prediction efforts to predict drought‐breaking rain such as occurred in early 2020.

Paper: Freund, M. B., Marshall, A. G., Wheeler, M. C., & Brown, J. N. (2021). Central Pacific El Niño as a precursor to summer drought‐breaking rainfall over southeastern Australia. Geophysical Research Letters, 48. https://doi.org/10.1029/2020GL091131