They are giant conveyor belts of water in the sky, moisture-rich storms that roll in from the Pacific Ocean a few times a year to fill California’s reservoirs… But distinguishing a good atmospheric river storm — a modest one that can help end a drought — from a catastrophic one that can kill people has been elusive. On Tuesday, that changed, as scientists published the first-ever scale to rank the strength and impact of incoming atmospheric rivers, similar to the way hurricanes are classified.

Related articles:

• San Francisco Chronicle: California storms to get a rating from 1 to 5, like hurricanes
• Scientific American: Warning scale unveiled for dangerous rivers in the sky