Trivia 006: ARkStorm

Hello everyone, how’s the weather where you are? The east coast may have been getting hammered, and they even got snow down in my home state of New Mexico. But here the weather’s been unseasonably balmy. It was almost, but not quite, t-shirt weather today. It’s been a far cry from the huge amounts of rain and snow we had in December and January. At least it didn’t rain for forty days and forty nights. But such a flood of biblical proportions has happened, and could happen again. On that note, I have some bad news for those of you who live in California.

A large amount of the precipitation that hits the US west coast comes north from the warm waters and atmosphere around the equatorial Pacific Ocean. Carried north and east by wind currents, it eventually makes land fall and deposits its moisture as precipitation. But occasionally an unusually high amount of moisture surges upwards. This is known as an atmospheric river, sometimes colloquially called the “pineapple express”. You can watch these massive air currents thanks to NASA’s GOES-West weather satellite. These atmospheric rivers can deposit as much as 50% of the west coast’s annual precipitation. This can be great, as it gives us water, but also devastating, as excess rain and snow can cause flooding, landslides, and other disasters.

In 1862, a particularly prolonged atmospheric river hit California. This dumped rain for forty-three days in most parts of the state. As a result, major flooding occurred, covering the Central Valley with water up to depths of 30 feet. The city of Sacramento was completely flooded, causing the newly-elected governor to have to travel by rowboat to his inauguration ceremony. (It’s almost like building your city on a site known for flooding is a bad idea).

In southern California, fully one-quarter of the 800,000 cattle living there died. This hastened the area’s transformation from ranching to farming. Ultimately, the flood caused over $3 billion of damages (in 2021 dollars) and killed 4,000 people. But the damage wasn’t just limited to California; Oregon, Nevada, Utah, Arizona, and New Mexico all saw their share of flooding as well.

The 1862 flood was the worst flood in Californian history. But geologic evidence has found that there was an even more massive flood in 1605, at least 50% more powerful than any other in the geologic record. The US Geologic Survey (USGS) estimates that such storms occur roughly every 500 to 1000 years. But climate change will likely exacerbate this issue, causing frequent storms to become more frequent. They have termed such an event an “ARkStorm” (short for “Atmospheric River 1000 storm). In addition to all the rainfall such an event would bring, it would likely cause dams and levees across the state to fail, causing yet more flooding. The USGS predicts that major parts of California will be under as much as 20 feet of water.

So enjoy the good weather while it lasts! And maybe buy an emergency rowboat if you live in California.

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