Atmospheric rivers - long, narrow streams of high water vapour transported in the atmosphere - are associated with up to 75% of extreme wind and rainfall or snowfall events over mid-latitude coasts, reports a study published online this week in Nature Geoscience. The study suggests that atmospheric rivers therefore represent a significant global hazard, both because of high winds and large amounts of precipitation and flooding potential.

Atmospheric rivers have previously been linked to a number of regional hydrological extremes, such as flooding and occurrences of extreme rain- and snowfall. However, their role in wind extremes has received less attention, and their impacts have not been investigated systematically at a global scale until now.

Duane Waliser and Bin Guan used a global detection algorithm together with reconstructions of atmospheric conditions for the period 1997 to 2014 to quantify the global impact of atmospheric rivers. They found that up to half of the most extreme 2% of wind and rain- or snowfall events are associated with atmospheric rivers. In western Canada, northern Europe, New Zealand and southern South America, atmospheric rivers occur on about 30-35 days per year. Their analysis of large insurance losses (over US$1 billion) during European windstorms between 1979 and 2003 reveals that 14 out of the 19 largest loss events were linked to atmospheric rivers.