Extreme rainfall has become intense and more frequent globally; however, in Australia, long-term changes in the extreme is not well understood. Using existing indices to study the mean and extreme rainfall events rarely show significant long-term changes in Australia. Often rainfall events are studied using a threshold, wet or all day percentiles, maximum consecutive rainfall event over a fixed number of days which might not cover a full length of rainfall event or might clump multiple events together. Thus, possible changes in the intensity and frequency of rainfall events in Australia remain unclear.

Here we use a persistent rainfall event-based approach – where a rainfall event is defined by the consecutive rain days (i.e. r×event), to study the changes in intensity and frequency of rainfall events. Note that these rainfall events might not be one single weather event. We categorise the events into four types of events based on the event length, 1-2 day event (maximum two consecutive rainfall), 3-4 day event (consecutive rainfall of 3 or 4 days), 5-6 day event (consecutive rainfall of 5 or 6 days) and >6-day events (consecutive events of more than 6 days). We find that the short duration rainfall events (1-2 day) have become more frequent as well as intensified since the beginning of the 20^th century, implying a more sporadic rainfall in Australia, especially the trends get stronger southward of the continent, increasing the potential of flash floods. The frequency in extended duration events, such as 3-4 day, 5-6 day and >6-day events have clear significant negative trends in the south and a positive trend in the north.

These trends are verified against previously rigorously tested observed station datasets to provide robust conclusions. Overall, changes in persistent rainfall characteristics provide much more spatially consistent results than the indices used previously.