‘Biblical’ Floods Hit California Every 200 Years – the Next One Is Due 

The recent storms in California have been big news across the world and with good reason – a state of emergency has been declared and people have been evacuated in the tens of thousands. But what many people may be less aware of is that even greater floods, ones of ‘biblical proportions’ as described by The Verge, are due some time soon, if history is taken as an indicator.

Such epic storms have visited the region roughly every 200 years for the past 2,000 years or more, climate scientists Michael Dettinger and Lynn Ingram pointed out in 2013.

The last such event was a series of storms lasting for 43 days between 1861 and 1862. California’s Central Valley was transformed into an enormous lake, and thousands of people drowned. The state government had to relocate from Sacramento to San Francisco.

We are now in the final quarter of the 200-year period since the last big event, and researchers with the US Geological Survey say “it appears that California may be due for another episode soon.”

The experts have used a simulation called the ARkStorm to examine what effects a disaster on the scale of the last would have today. They found that a 300-mile-long and 20-mile-wide portion of the Central Valley would be under water. Cities the length of the California coast would flood, winds would reach 125 miles per hour and roads would be rendered impassible by landslides.

The Mississippi River times 20

Despite the devastation of the recent storms, they can’t be compared in terms of scale to the ‘biblical’ ones of the past and, possibly, the future. They are of a similar nature, however.

Marty Ralph, director of the Center for Western Weather and Water Extremes at the University of California, San Diego, explained that both result from an atmospheric river, a phenomenon first identified in 1998.

An atmospheric river is a massive ribbon of water vapor that flows off the Pacific Ocean and combines with strong, low-altitude winds. They measure around 250 to 375 miles across, reaching lengths from 1,000 to 2,000 miles or even greater.

“It’s about the equivalent of 20 Mississippi Rivers’ worth of water, but it’s in the form of water vapor rather than liquid,” Ralph said.

The stream of warm, wet air is forced upwards when it hits coastal mountains, after which it cools and condenses into vast rain clouds.

“It’s definitely a very unusually very wet year for us,” Ralph noted, but he doesn’t believe we’re in an ARkStorm type of year.

“Now that’s not to say that couldn’t happen, which would be highly tragic,” he added.

In an average year around nine atmospheric rivers play a part in California precipitation. There have been a massive 30 since October 1st.

“When we get a sequence of them, or we get too many and the soils are real moist and the rivers are high and the reservoirs are full, then they can go from being largely beneficial — because we need water in the West — to hazards,” Ralph explained.

The increase is unlikely to be a rarity. As global temperatures continue to rise, atmospheric rivers get warmer and wetter, bringing with them more flooding.

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Image credit: Thinkstock

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