Rivers in the sky
Atmospheric bands of water vapor can cause flooding and extreme weather
Scientific conferences usually don’t physically experience their subjects. But during a session on “atmospheric rivers” last December at a geophysics meeting in San Francisco, one of those very rivers was barreling down on meeting attendees.
Like freight trains loaded with water vapor, atmospheric rivers are long, narrow bands whose winds funnel huge amounts of moisture through the sky. When they hit coasts, these rivers can drop their moisture as rain and cause destructive flooding, as in January 2005 when more than 20 inches of rain soaked southern California, killing 14 people and causing hundreds of millions of dollars in damage.
Scientists (and San Francisco) managed to escape December’s atmospheric river without such harm, but the storm dumped more than 10 feet of snow in parts of the Sierra Nevada, putting the mountains on track for their wettest recorded season. That sort of impact underscores why researchers have recently become fascinated with atmospheric rivers. Completely unknown just over a decade ago, these rivers turn out to be not only a key factor in Western flooding and water supply, but also a major player in the planet’s water cycle.