Global scale impact of atmospheric rivers on the severity of flooding

Atmospheric rivers (ARs) are narrow, elongated corridors of concentrated moisture that transport substantial amounts of water vapour from the tropics to the mid-latitudes. These meteorological phenomena are known to significantly influence extreme precipitation events and are often linked to major flood occurrences. Despite their recognized importance in regional hydrology, the overall contribution of ARs to global flood risk—the hazard posed by extreme precipitation events—has not been comprehensively quantified. In this study, we assess the relationship between ARs and extreme hydrological events using data from 2686 largely regulation-free catchments distributed across the globe. Our findings reveal that on a regional scale, ARs are responsible for over 70% of the largest precipitation and streamflow events in the last four decades. Furthermore, AR-related precipitation leads to a significant reduction in the recurrence intervals of these extreme events, increasing the likelihood of large-scale flooding by a factor of 2 to 4. In certain regions, such as parts of North America, Europe, and Australia, rare flood events are up to 12 times more likely when ARs are present. These results underscore the critical role that ARs play in driving the frequency and severity of extreme hydrological events globally. Our findings highlight the need for greater attention to the influence of ARs on flood risk, particularly as climate change may alter their frequency and intensity in the future.