Atmospheric Rivers intensify extreme precipitation and flooding across Australia

Atmospheric rivers (ARs) are narrow corridors of intense water vapor transport in the atmosphere. While the link between atmospheric rivers and extreme precipitation has been established across many regions of the world, the relationship between atmospheric rivers and flooding, the ultimate hazard resulting from extreme precipitation, remains poorly understood. Utilizing 467 Hydrologic Reference Stations (HRS) across Australia, the contribution of ARs to extreme precipitation and flooding is investigated by calculating the probability of occurrence of an AR on peak over threshold (POT) event days using different lag periods. By examining the tail behaviour of heavy precipitation and flooding caused by ARs, using the Generalized Pareto distribution (GPD), the magnitude to which ARs impact extreme events, and how this varies with event severity, is also quantified. Here, we find that southeast Australia has the highest AR concurrence (around 75- 100%) with extreme precipitation and streamflow events. The median magnitude of extremes is 20 to 70% higher in the presence of an AR. In addition, the return periods of extreme flood and precipitation events of a given magnitude are on average 2 to 12 times shorter when they coincide with an AR compared to when they do not coincide with an AR. Our study highlights that ARs are a major factor in significantly increasing the frequency of extreme weather events in different regions of Australia. This suggests a need to incorporate AR impacts in hydrological modelling to enable better water resource management and flood risk assessment. • Atmospheric Rivers (ARs) are linked to extreme precipitation/streamflow in Australia • ARs are present on 70-90% of days with extreme precipitation and flooding • ARs increase 20-year flood frequencies by a factor of 2 to 12 across Australia