The drivers of extreme rainfall event timing in Australia

Abstract

Australia experiences some of the world's most variable rainfall. Previous studies have mostly focused on understanding rainfall variability in terms of frequency and intensity. However, understanding the timing of when extreme rainfall occurs is crucial for seasonal prediction, although it largely remains unexplored. Here we investigate the timing of extreme rainfall in Australia and the spatial variability of this timing. This study examines how some of the large-scale drivers, such as the El Niño-Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO), determine the timing and interannual variability of the timing of extreme rainfall in Australia. Our results show that there is a clear spatial north-south

Fundamental Ingredients of Australian Rainfall Extremes

“…In all three regions there is clear seasonality to rain intensity, with the T1 and tercile 2 (T2 hereafter) days showing relatively even distribution throughout the year and a stronger skew toward the Southern Hemisphere summer months (November to February) as the rain intensity increases. That is to say, the greatest number of T3 and top 100 days occur in the tropical wet season (DJF) for Darwin (in agreement with the findings of Dey et al (2021), who found, using AWAP, that extreme rainfall in northern Australia usually occurs in austral summer), and the summer months (NDJF) for both Brisbane and Melbourne. This latter result is in contrast to Dey et al (2021), who found that in southern Australia extreme rainfall usually occurs in the autumn and winter months, but that the timing is highly variable and that in southeastern Australia extreme rainfall can fall at any time of the year.…”

“…This latter result is in contrast to Dey et al. (2021), who found that in southern Australia extreme rainfall usually occurs in the autumn and winter months, but that the timing is highly variable and that in southeastern Australia extreme rainfall can fall at any time of the year. This clear shift in the seasonality of rain intensity in all regions indicates that studying the settings of extreme rainfall events remains important for the prediction of extreme rainfall.…”

“…That is to say, the greatest number of T3 and top 100 days occur in the tropical wet season (DJF) for Darwin (in agreement with the findings of Dey et al (2021), who found, using AWAP, that extreme rainfall in northern Australia usually occurs in austral summer), and the summer months (NDJF) for both Brisbane and Melbourne. This latter result is in contrast to Dey et al (2021), who found that in southern Australia extreme rainfall usually occurs in the autumn and winter months, but that the timing is highly variable and that in southeastern Australia extreme rainfall can fall at any time of the year. This clear shift in the seasonality of rain intensity in all regions indicates that studying the settings of extreme rainfall events remains important for the prediction of extreme rainfall.…”

“…Unlike previous studies of localized Australian rainfall events, which have tended to focus heavily on southern Australia and the eastern coast (e.g., Ashcroft et al, 2019;Avila et al, 2015;Dey et al, 2019Dey et al, , 2021King et al, 2013b;Pepler et al, 2019Pepler et al, , 2021Warren et al, 2021), we extend our focus from the tropics to mid-latitudes and choose three regions of study centered on the cities of Darwin (tropical), Brisbane (subtropical) and Melbourne (mid-latitude, although Melbourne still has some sub-tropical aspects to its climate), respectively. These areas are chosen to develop a methodology that is universally applicable from tropical to mid-latitude regions (given that the findings of Norris et al (2019); Wood et al (2021), indicate the importance of understanding precipitation extremes from the tropics to mid-latitudes).…”

“…Berry et al (2012), Berry and Reeder (2016), and Narsey et al (2017) argue that Rossby wave disturbances originating in the mid-latitudes account for more than half of the wet season rainfall in northern Australia, and Hoang et al (2016) examined the links between extreme rainfall in northern Australia and synoptic-scale potential vorticity (PV) disturbances, many of which have connections to the mid-latitudes. The range of seasonal variability of these rainfall drivers and their interactions all influence the frequency, intensity and timing of extreme rainfall in Australia (e.g., Dey et al, 2021), and instances where these weather systems co-occur are particularly likely to cause precipitation extremes.…”