Editor’s note: Marshall Brain – futurist, inventor, NCSU professor, writer and creator of “How Stuff Works” is a contributor to WRAL TechWire.  Brain takes a serious as well as entertaining look at a world of possibilities for Earth and the human race.  He’s also author of “The Doomsday Book: The Science Behind Humanity’s Greatest Threats.” Brain has written several posts recently about the threat of climate change. His exclusive columns written for TechWire are published on Fridays.

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RALEIGH – Imagine that you live in the state of California. It’s a popular option in 2022, with approximately 40 million Americans choosing California as their home.

For people living in California, there are already two doomsday scenarios to be thinking about on a regular basis. The first is the earthquake problem. California unfortunately sits on top of several major earthquake fault lines that have a history of doling out catastrophe. For example, San Francisco was destroyed in the 1906 earthquake and then hit again by a major quake in 1989.

And then there is the water situation, which seems is getting more critical by the day. The drought’s effects include problems with crop failures, wildfires and, eventually, drinking water scarcity.

The water scarcity problem has become so significant that California’s governor has announced the state’s plan for spending $8 billion to address it.

But then last week a new doomsday scenario for Californians appeared on the radar seemingly out of nowhere – the California Megaflood.  This is the opposite of water scarcity. And if we believe the predictions, a megaflood could be the worst possible disaster that California could face.

California’s Historical Record of Megafloods

If we get in our time machine and set the dial for 1862, we can witness the kind of megaflood that scientists are now talking about anew. This megaflood even has its own Wikipedia page: The Great Flood of 1862

“The event dumped an equivalent of 10 feet (3.0 m) of water in California, in the form of rain and snow, over a period of 43 days.”

Think about a major hurricane that makes landfall in the United States. Hurricanes can cause massive flooding because they can dump 12 or even 18 inches of rain on an area over a couple of days. The Flood of 1862 was caused by 120 inches of rain. It is easy to imagine streams and rivers rising to unprecedented heights in such a deluge. And this did happen, with everything along the banks plus bridges and dams getting washed away. But perhaps the most devastating thing about the Flood of 1862 was the lake that formed in the Central Valley of California. Imagine a lake 300 miles long, 20 miles wide, encompassing perhaps three million acres, that forms spontaneously from all the rain and runoff. It took months for this lake to evaporate and soak into the ground. This video shows how it happened – https://www.youtube.com/watch?v=GjSh7wxr0IA

An optimist might think, “OK, so maybe a megaflood has hit California before. That was probably a fluke, never to be repeated again.” Unfortunately, geologists have discovered plenty of evidence for earlier megafloods in the region, happening fairly regularly every 200 years or so apart. This article points out that there is evidence for megafloods hitting California in “212, 440, 603, 1029, c. 1300, 1418, 1605, 1750, 1810, and 1861–62.” This steady pattern is what is causing the concern among scientists today. Megafloods in California seem to be regular events, and therefore the scientists ask:

  1. When will the next megaflood hit California?
  2. Will climate change supercharge the flooding and make things even worse?

What scientists are predicting

The problem with a warming climate is that it can have two opposing effects on the weather. When things are dry, the warmer climate makes things even drier. So we see longer, more persistent droughts on the one hand. On the other hand, when things are wet, they become even wetter, and we can see extreme flooding events. This happens because warmer air can hold more water vapor in the same volume of air.

We saw one of these extreme flooding events in Kentucky this summer, with 10 inches of rain falling in just 2 days. This intense rainfall was not caused by a hurricane, but instead is the effect of normal storms that have been amplified by climate change and intense atmospheric rivers of moisture – https://www.youtube.com/watch?v=Jw2lrQ5zst4

These extreme flooding events have been happening around the world:

Scientists are expecting the same kind of phenomenon to occur in California. Since there is already a historical pattern for these megafloods, climate change has the potential to make future megafloods more intense and more frequent.

The problem is that a California megaflood that occurs today will be incredibly devastating compared to the megaflood that occurred in 1862. The population of California has grown by a factor of 100 since 1862, and the amount of development and agriculture to be wiped out has expanded in the same way. Some estimates for megaflood damage range as high as $1 trillion, with the potential for hundreds of thousands of people to die in the floodwaters.

Like an earthquake, we do not have a way to pinpoint the day when the next megaflood will happen. Like an earthquake, there is no way to prevent a megaflood. Unlike an earthquake, which tends to be localized to just one city, the next megaflood can impact a much larger region. If the next megaflood forms a gigantic lake like the last one did, 6,000 square miles of property could be inundated in the Central Valley. That’s an area the size of Connecticut.

Sources