John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Imagine the amount of water pouring out the mouth of the Mississippi River, times 15. That's what these things move through the air over time.
Last winter, rain-swollen storms gave the UK a drenching it won't soon forget: waves lapped against houses, mired cars became live-human traps, people were crushed by falling trees and drowned in boiling rivers. Lumped in with the damage caused by the summer's also-bad floods, the blow to the country's coffers totaled about $1.6 billion.
And that most foul year could be just the beginning of decades of flooding, according to researchers from the University of Reading and the University of Iowa. These scientists are concerned about the meteorological movers behind the UK's recent floods: vast channels of moisture in the sky known as "atmospheric rivers" that convey great amounts of water over the globe.
Look, here's a river about to hit California in December 2010. By the time it passed, 26 inches of rain had fallen on the state and the Sierra Nevada mountains sported a new 17-foot-tall cap of snow:
And this is one of the latest rivers to lick the United States, in the winter of 2012:
Atmospheric rivers are responsible for some of the most prolonged, punishing storms around. Imagine the amount of water pouring out of the mouth of the Mississippi River, and then increase it by 15 times to understand what a really big atmospheric river moves through the air over time. These things are responsible for some of nature's worst storms, such as 2010's "Snowmageddon" and the 2005 rains in Southern California that prompted mudslides, killed 14 and caused up to $300 million in destruction.
An occasional visit from one of these floating beasts can be nasty enough. But the researchers are concerned that the paths these rivers historically take are changing direction and moving toward Britain. Why is that? They point the finger at the increasing amounts of CO2 that humans are pumping into the atmosphere. Says lead researcher David Lavers:
"ARs could become stronger in terms of their moisture transport. In a warming world, atmospheric water vapour content is expected to rise due to an increase in saturation water vapour pressure with air temperature. This is likely to result in increased water vapour transport.
"The link between ARs and flooding is already well established, so an increase in AR frequency is likely to lead an increased number of heavy winter rainfall events and floods. More intense ARs are likely to lead to higher rainfall totals, and thus larger flood events."
The scientists reached this grim conclusion using several different climate models. They successfully simulated atmospheric rivers from 1980 to 2005, and then projected the models forward from the year 2074 to 2099 to get this array:
Like psychedelic leeches (red is the most dense concentration of water vapor), the rivers seem almost attracted to the UK and a sizable chunk of western Europe. In their study, the researchers don't really give any ideas for counteracting these monstrous streams of moisture. Perhaps it will be something we'll just have to adapt to, perhaps by getting really good at doggy paddling.
Top image: Firemen attempt to rescue passengers of a van during flooding in Gloucester in November 2012. (Andrew Winning / Reuters)