EXPERT REACTION: La Niña has ended, El Niño watch begins

The months of April/May in southeast Australia have seen significantly below average rainfall since the 1990s because of changes in the jet stream.

In late autumn The Indian Ocean Dipole is not active as a climate driver. Neither the Southern Annular Mode (SAM) nor the phase of ENSO is strongly linked to rainfall in southeast Australia at this time. However, a negative phase of the Southern Annular Mode currently is likely to produce hotter conditions in parts of southeast Australia in the short term. Once it returns to neutral or even positive SAM, frontal systems will again be pushed southward meaning that the cooler months should again return to below average rainfall, especially if an El Nino develops during the winter months.

The Bureau’s declaration that La Niña has ended heralds the official end of the “big wet”, a rare triple-dip La Niña that was only the fourth since 1900 and the first in 22 years. This period saw Sydney’s wettest year on record, and led to what turned out to be Australia’s largest insured loss event ever in the February – March NSW and QLD floods. Current insurance industry reported losses for this event sit at AUD 5.76 bn, which now surpass the 1999 Sydney hailstorm (AUD 5.57 bn) as Australia’s largest.

Many international models now point to the development of El Niño in late 2023. This, combined with significant fuel growth over the previous seasons, means bushfire risk will be high. In fact, research by Aon and partners Climalab here suggests that the triple-dip La Niña may have tipped the Pacific ocean circulation into a long-term El Niño like state that could now persist for the coming decade. Australia’s big wet could soon become the big dry.

The 3-year La Niña event has come to an end, but it’s not clear yet what comes next. Predicting how the Pacific Ocean and atmosphere will evolve from this time of year (March-May) is notoriously difficult, because the region is very responsive during this season to sudden changes in, among other factors, wind speeds over the western Pacific. For example, in 2014, forecasts around this time of year pointed to an El Niño developing in the latter half of 2014; instead, those early signs fizzled out, and an El Niño only developed a year later in late 2015. So while most forecast models now predict an upcoming El Niño, I wouldn’t place any bets just yet.

The Earth's climate is like a pendulum; it's not that unusual to swing into an El Niño after a La Niña.

Now is the time to start cutting back the excess vegetation that grew over the last three years. All it takes is a dry winter and spring, which is probable with an El Niño, and all that excess vegetation will be fuel for summer bushfires.