‘Rivers in the sky’ threaten more flooding for California
UNITED STATES: Giant plumes of water vapour known as atmospheric rivers are surging across the Californian sky, wreaking havoc.
They are typically hundreds of kiloemtres wide and carry more water than the Amazon or the Mississippi.
Extending back to the Tropics, they funnel vapour thousands of miles through the air and dump it as record quantities of snow and rain on the state, which until recently was suffering from drought. ‘‘We usually see three or four atmospheric rivers in a season,’’ Scott McGuire, a meteorologist with the National Weather Service in Reno, Nevada, said. ‘‘We’ve already had ten.’’
Recent research has shown that atmospheric rivers are among the most dangerous weather systems.
A study published in the British journal Nature Geoscience last week looked at two decades of storms in non- tropical parts of the world and found that as many as half of the windiest and wettest storms were inflicted by these rivers in the sky, and that they were also responsible for up to three quarters of large storms along coastlines.
Duane Waliser, an atmospheric scientist at Nasa’s Jet Propulsion Laboratory and lead author of the study, said that the winds associated with atmospheric rivers were typically twice as fierce as those in an average storm.
In the past 20 years Europe has had 19 storms that caused at least a billion dollars of damage. ’’We associated atmospheric rivers with 14 out of the 19,’’ Waliser said.
In California this northern winter, atmospheric rivers have been at least partly beneficial.
The US Drought Monitor said last week that less than 20 per cent of California now faces drought conditions and that nowhere in the state is suffering from extreme or exceptional drought.
A year ago 90 per cent of California was in drought.
However, snow in the Sierra Nevada mountains is so deep that ski resorts are having to dig piste markers, chair-lifts and ski patrol huts out of snow drifts.
The storms have also brought flooding, power cuts, felled trees and caused many fatal or nearly fatal car crashes. In Los Angeles last weekend firefighters rescued a woman from a 7m sinkhole in a road a few miles from Universal Studios.
She was found standing on top of her car, which was upside down in rushing water.
Further north, thousands of homes were evacuated this month for fear that the Oroville dam, America’s highest, was about to fail. It held, thanks to an emergency spillway that had never been used before and the frantic efforts of construction crews to reinforce it.
‘‘Most of the reservoirs are full and the amount of snow is very high, so everything we get now is going to cause some problems,’’ Jan Null, of Golden Gate Weather Services, said. - The Times