The atmospheric river, one of many to hit California this winter, brought heavy rainfall that set off flooding across the state this weekend.
California was hit by torrential rains brought about by a new atmospheric river this weekend, which triggered flooding and blackouts and prompted evacuations across the state, including greater Los Angeles, the San Francisco Bay area, and metropolitan Sacramento.
Intense wind and rain destroyed trees, damaged cars, and homes, and pulled down power lines across the state, which is struggling to recover from months of extreme weather.
The storm, which originated near Hawaii and brought between 3 and 10 inches (7.6-25.4cm) of rain across a region that is home to 26 million people, is just the latest blast of heavy showers and gusty winds to batter California, which has been battling record-breaking droughts and wildfires for years. 10 atmospheric rivers have hit California since Christmas, leading to one of the wettest and snowiest winters in recent times.
On Friday, US President Joe Biden issued a disaster declaration for 35 counties, unlocking federal assistance to support local authorities and rescue teams. On the same day, California Governor Gavin Newson issues an executive order to ease restrictions on capturing water from the heavy storm to boost groundwater recharge storage.
In San Luis Obispo County, authorities spent the day monitoring levees, creeks, and rivers and issued evacuation orders and warnings affecting about 2,000 residents. A failed levy led to flooding in low-lying areas across the county, damaging homes and businesses. A roadway in Paso Robles collapsed for the second time since January, trapping a few hundred residents outside the town.
What Is an Atmospheric River
An atmospheric river is a long, narrow band of moisture in the atmosphere – akin to a river in the sky – that extends from the tropics. These storms, which can carry up to 15 times the Mississippi River’s volume, are responsible for most of the flood damage in the Western US.
While atmospheric rivers are nothing new, a 2018 study suggests that global warming will cause these events to become 25% longer and 25% wider, carrying more water and thus becoming more calamitous, escalating the threat of flooding, landslides, and damage to communities. This is because warmer air has the capacity to hold and release more moisture; for each 1C of warming, saturated air contains 7% more water vapour.
California’s years-long drought is exacerbating the situation. Years of dry weather have left parched soil compact, making it increasingly difficult to absorb groundwater and thus leading to a higher risk of flooding and less storage water. Reservoirs across the state are exceptionally dry and even this winter’s exceptional rains will not be enough to solve the ongoing drought, the worst in more than 1,200 years.
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