What’s behind Australia’s shifting rainfall? New study explores weather objects

Australia’s rainfall is changing in distinct and important ways. Summers in the tropical north are getting wetter, while winters in the southeast are becoming drier.  

New research led by Dr Chenhui Jin at Monash University has taken a fresh look at the weather systems that modulate seasonal rain across the continent, helping to explain the causes of both long-term shifts and year-to-year variability.

The study objectively identifies six types of weather systems – cyclones, anticyclones, fronts, warm conveyor belts, Rossby wave breaking events (indicated by elongated potential vorticity streamers) and cut-off lows – and shows how their presence or absence can account for seasonal rainfall across Australia.

In summer, tropical cyclones dominate rainfall in the north. In places like the Kimberley and the Top End, they account for over 60% of the wet season total. In winter, systems linked to Rossby wave breaking in the upper atmosphere are responsible for up to 50% of rainfall in Victoria and southern South Australia.

Importantly, the research showed that weather systems across Australia can act together, creating continent-wide patterns of dry or wet months. The team identified recurring clusters of monthly rainfall linked to changes in the behaviour of these systems. These help explain why, for instance, eastern Australia might be drenched while the west stays dry.

The team analysed 40 years of data and found that the frequency of different rainfall-producing systems has changed between two consecutive periods. Summers in northern Australia have become wetter, largely due to more rainfall from cyclones. At the same time, winters in the south have dried out. That’s partly because the weather systems that typically bring winter rain – like wave-breaking events and warm conveyor belts – are appearing less often.

By objectively identifying weather systems, the research gives scientists a clearer picture of how weather systems affect wet and dry conditions across the Australian continent.

The research has been published in the Quarterly Journal of the Royal Meteorological Society and is available here.

This article was written using a combination of human and artificial intelligence