The Coming California MegaFlood

Investment Analysis Clubs Macro Economic Trends and Risks
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Interesting subject in the NY Times and other papers recently, covering the results of a new study about the risks of a month-long (+/-) atmospheric river of moisture hitting California and causing unbelievable flooding. Turns out these have happened numerous times in the last millenia, most recently in 1861-62. The new study projects that the warming climate is increasing the risk of such a storm.

https://www.usatoday.com/story/news/nation/2022/08/13/califo…
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While intense droughts, wildfires and earthquakes are typically the main concern across the West, the study released Friday warned of another crisis looming in California: “Megafloods.” It notes climate change is increasing the risk of floods that could submerge cities and displace millions of people across the state. It says an extreme monthlong storm could bring feet of rain – in some places, more than 100 inches – to hundreds of miles of California.
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A NY Times article on this subject (https://www.nytimes.com/interactive/2022/08/12/climate/calif… ) says that the new study indicates that with current levels of atmospheric warming we’ve increased the risk of a California mega-storm to about 1/50 for a given year. A warmer atmosphere holds more water that can rain out of the sky in the right conditions, and if we increase the global temperature another 1 degree C, that would go to 1/30.

A 2013 Scientific American article covered the subject and has a graphic of the “inland sea” created by the 1862 storm, covering areas where millions of people now live.

https://cw3e.ucsd.edu/wp-content/uploads/2013/10/Dettinger_I…

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The intense rainstorms sweeping in from the Pacific Ocean began to pound central California on Christmas Eve in 1861 and continued virtually unabated for 43 days. The deluges quickly transformed rivers running down from the Sierra Nevada mountains along the state’s eastern border into raging torrents that swept away entire communities and mining settlements. The rivers and rains poured into the state’s vast Central Valley, turning it into an inland sea 300 miles long and 20 miles wide…Downtown Sacramento was submerged under 10 feet of brown water filled with debris from countless mudslides on the region’s steep slopes. California’s legislature, unable to function, moved to San
Francisco until Sacramento dried out—six months later. By then, the state was bankrupt.
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As our nation’s most populous state, and a massive economic engine for both the nation and the world, such a disaster would have widespread macroeconomic implications. If the recent study is right, then chances are good that many of us may see such an event in our lifespan.

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The latest in media “severe weather” hysteria? I remember the hype, decades ago, about a supposed earthquake causing California to slide into the ocean.

Steve

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The latest in media “severe weather” hysteria?

Yes and no. If you’ve ever driven through California’s Central Valley, it’s obvious it’s a giant flood plain. That’s the source of the flat and fertile land. The only question is what causes the floods.

Is it heavy rainfall, possibly triggered by warm, moist air rising up to get over the Sierras? Or is it a fast melting snow pack of the higher Sierras running down and flooding the land?

Apparently these scientists think the former is more likely than the latter.

—Peter

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Is it heavy rainfall, possibly triggered by warm, moist air rising up to get over the Sierras? Or is it a fast melting snow pack of the higher Sierras running down and flooding the land?

Apparently these scientists think the former is more likely than the latter.

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It is both. The warm moist tropical ARs hit the Sierras and dump warm rain to get over the Sierras, which melts the Sierra snow pack causing torrents of rain and melted snow come down the many Sierra rivers to flood the Central Valley.

Jaak

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The latest in media “severe weather” hysteria?

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Unfortunately this is not hysteria. It is related to new California normal of heat, drought, fires and ARs.

Jaak

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We’ve had a variety of flooding, whether it’s a problem relies of a bazillion gallons of water being sucked up into the atmosphere then magically released in all the right places… Rivers were famed to handle it over the millennia, I think there are some crackpots just stirring up more fears, and such as they always have… So they flood, we’ll grow rice instead of wheat, other grains, almonds, peached love a lot of water… The farmers or corporate owners will deal with it…

Ignore the fear mongers of a certain bent… P-Box 'em!

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The latest in media “severe weather” hysteria? I remember the hype, decades ago, about a supposed earthquake causing California to slide into the ocean.

So, which will happen first, The Big Quake or The Big Flood?

DB2
No longer living in California

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The atmospheric river megafloods are obviously a hazard; we know there was one just 160 years ago. That said, the paper does take the high end projections.

Two examples:

  • The authors used an extreme high-end projection for future greenhouse gas emissions (RCP8.5 scenario).
  • The authors used several different models; they noted that there were substantial difference in the amount of precipitation and went with one called CESM1-LENS, the one “exhibiting the largest precipitation accumulations”.
    www.science.org/doi/10.1126/sciadv.abq0995

DB2

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Believe it or not my great, great uncle died in the great flood of Pico (So. Cal.). He was a bean farmer. After 70 years I would like to see a flood in So. Cal. We have some of the best flood control in the world. Some coastal areas will flood but there on the water and have great insurance. I takes a east coast paper to talk about a west coast flood.

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Gosh, all it means is that large scale long term planning in the state needs to ask "What can we do now that would be cost effective for such a radical real rare threat?You knowm prudential thinking, long term investment planning, civil order…

Oh, we don’t do that anymore. Mostly, we never did.

I vaguely remember something about why the Dutch have done so well.

david fb

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The latest in media “severe weather” hysteria?

Yes and no. If you’ve ever driven through California’s Central Valley, it’s obvious it’s a giant flood plain. That’s the source of the flat and fertile land. The only question is what causes the floods.

Is it heavy rainfall, possibly triggered by warm, moist air rising up to get over the Sierras? Or is it a fast melting snow pack of the higher Sierras running down and flooding the land?

Apparently these scientists think the former is more likely than the latter.

The unofficial big word for the day is “Geomorphology” which is a fancy way of saying the geological reasons for the way a landscape looks.

https://en.wikipedia.org/wiki/Geomorphology

Even if there are periodic mega floods the reason that the central valley looks the it does is likely mostly a combination of gradual erosion from mountains on both sides of the valley and the glaciers that carved out places like Yosemite Valley. I don’t think that the glaciers got down into the central valley but I did not double check that.

The heavy rain pattern is sometimes call “The Pineapple Express” since and atmospheric river will stretch from Hawaii to the west coast.

https://en.wikipedia.org/wiki/Pineapple_Express

I was living in Portland Oregon in 1996 when this developed, along with some other unusual weather patterns, which caused widespread flooding around Portland Oregon. My house actually had some minor flood damage even though it was on top of a 20 foot berm that was maybe a half a mile from a sluggish river that was normally around 20 feet wide and maybe 6 feet deep.

People often greatly underestimate the risk if infrequent events. For example you might have some thing like a 500 year flood risk but if you live in some place for 50 years there is about a 10% chance of that happening during your lifetime. Likewise there would be about a 5% chance of a 1000 year flood happening in 50 years.

Even without climate change weather prediction is difficult because most areas have very limited weather. Flood records that go back more than about 100 years are mostly anecdotal stories and newspaper accounts of floods.

It is not related but if you want to hear about some floods of truly biblical proportions read up on the Missoula floods. https://en.wikipedia.org/wiki/Missoula_floods

Basically at the end of the last ice age there were ice dams around Missoula Montana which formed lakes the size of the great lakes. When the ice dam broke it sent a wall of water downstream and formed the Columbia River Gorge and flooded the area where Portland Oregon is in and hundreds of miles south. This happened repeatedly. It is not entirely clear but some Native Americans may have lived in the area then and some of their oral history could be related to that.

https://en.wikipedia.org/wiki/Pineapple_Express

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watty: People often greatly underestimate the risk if infrequent events.

YES! Just as with financial innumerancy, the failure to understand simple statistical language in large scale planning is insanely destructive and expensive.

I do expect big earthquakes will continue with greater frequency than big floods in California, but the terms of discussion of a mythical “Big One” earthquake is stoopid. California, not even the part west of the San Andreas fault, is not going to fall into the ocean nor anything like. And in terms of earthquake safety, from the late 1980’s on I always felt safer in earthquake aware and building code updated Los Angeles than places like St Louis. Huh?, well check out the New Madrid earthquakes

https://en.wikipedia.org/wiki/1811–1812_New_Madrid_earthquak…),

and ponder this:

“In a report filed in November 2008, the U.S. Federal Emergency Management Agency warned that a serious earthquake in the New Madrid Seismic Zone could result in “the highest economic losses due to a natural disaster in the United States”, further predicting “widespread and catastrophic” damage across Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and particularly Tennessee, where a 7.7 magnitude quake or greater would cause damage to tens of thousands of structures affecting water distribution, transportation systems, and other vital infrastructure.”

And yes, the New Madrid earthquake zone is a direct threat to the Old River Control Structure (actually there is a long and intimidating list of other equal or worse threats to the Old River Control Structure but we all just keep walking by while whistling a happy tune… For those who like disasters a medium big earthquake destroying buildings and wrecking big cities while permanently and radically changing the course of the lover Mississippi River via huge floods…well, it is hard to beat.

So, do we need to do a lot more thinking about the future? Nah, let the kids take care of it.

david fb

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Gosh, all it means is that large scale long term planning in the state needs to ask "What can we do now that would be cost effective for such a radical real rare threat?You knowm prudential thinking, long term investment planning, civil order…

Oh, we don’t do that anymore. Mostly, we never did.

You know, maybe some dams for flood control and power generation might help. We should get on that.

https://water.ca.gov/water-basics/the-california-water-syste…
California’s State Water Project (SWP) was constructed in the 1960s and 1970s to supply water to more than 27 million people and 750,000 acres of farmland. Planned, constructed,and operated by DWR, it is one of the world’s most extensive systems of dams, reservoirs, power plants, pumping plants and aqueducts and remains key to California’s economy. [bolding mine]

Oh. Looks like my idea is a bit too late.

I wonder how many dams and reservoirs there are in California.
https://en.wikipedia.org/wiki/List_of_dams_and_reservoirs_in…

1400 dams? 1300 reservoirs? What good is this lousy government anyway?

I get a little tired of government bashing in general, and California bashing specifically. So little of it is based in facts.

Now, is this enough to prevent this possible mega flood? Probably not. But this mega flood is likely a worst case scenario. And an awful lot has already been done to reduce flooding and provide water for the world’s 7th (6th? 5th? I gotta leave some research to others) largest economy.

Can more be done? That can almost always be answered in the affirmative. Something more can be done. The question is whether it is cost effective. In the middle of an historic drought, spending to mitigate a massive flood event isn’t going to gain sufficient political traction to get off the ground. But some thinking can be done and ideas tossed around. And that’s exactly what articles like this stimulate. A bit of thinking.

–Peter

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So, which will happen first, The Big Quake or The Big Flood?

You forgot the Great Coming California Tsunami.

No longer living in California

Maybe, anyone who moved to California after 1960 should go back to where it’s safer.

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Something more can be done. The question is whether it is cost effective. In the middle of an historic drought, spending to mitigate a massive flood event isn’t going to gain sufficient political traction to get off the ground. But some thinking can be done and ideas tossed around. And that’s exactly what articles like this stimulate. A bit of thinking.

The scale of changes needed to protect property against this threat is hard to imagine. Move Sacramento? Obviously not making it onto the agenda, lol. More realistically, California should be developing a plan for education of their population about the risk / early warning and progressively more intense warnings as the event develops / robust evacuation plans to minimize deaths, etc …

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Most people don’t know much about the New Madrid earthquakes of 1811–12, rather the fame goes the the San Francisco Quake of 1906. The 1811 New Madrid earthquakeS went on and on for months. Like you said, they changed the course of the Mississippi River.
But, OMG the San Francisco Quake. Actually, The City was rebuilt with far better standards. It was the devastating fires that lasted for several days which caused the high number of people who died.

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The scale of changes needed to protect property against this threat is hard to imagine.

Just need to install a big drain at the low point of the valley …

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particularly Tennessee, where a 7.7 magnitude quake or greater would cause damage to tens of thousands of structures affecting water distribution, transportation systems, and other vital infrastructure…a direct threat to the Old River Control Structure…

David fb,

Your comment on the New Madrid fault raises the spectre of mass casualty and catastrophic losses in a large area of hydrographic importance stretching west/southwest along a swath spanning from the Eastern Continental Divide to the eastern half of the Mississippi River basin.

https://upload.wikimedia.org/wikipedia/commons/1/15/NorthAme…
https://www.epa.gov/ms-htf/mississippiatchafalaya-river-basi…

Many people forget the massive size and impact of the Tennessee Valley Authority (“TVA”) area on not just power generation and infrastructure support systems but also on watershed development and flood control for an important swath of America’s agricultural and manufacturing economy.

Missouri, Arkansas and all of the “TVA Megasites” could experience dangerous flooding, including Huntsville (AL), Chattanooga (TN), Golden Triangle (Mississippi), Hopkinsville (KY), Memphis Regional, and West Kentucky Megasites.

https://en.wikipedia.org/wiki/Tennessee_Valley_Authority#Meg…

Just looking at a map of the TVA area compared with a map of the New Madrid Seismic Zone makes it obvious that one overlays the other, belying a natural correlation:

https://www.tvasites.com/maps/
https://dnr.mo.gov/land-geology/hazards/earthquakes/science/…

Even if St. Louis, Eastern Arkansas and all the TVA Megasites survived, a major quake in the New Madrid Seismic Zone could sufficiently disrupt the TVA flood control systems to inundate or obliterate parts of New Orleans and/or the US petrochemical infrastructure sites along the Gulf Coast.

Until your suggestion invoked my own investigation, I had no idea how destructive and economically significant a major New Madrid earthquake could be when hydrography is taken into account.

One may reasonably expect that the TVA agency and/or the Army Corp of Engineers has anticipated this very flood scenario. Surely the US government already has earmarked funds from our recent infrastructure and climate bills for projects mitigating such events.

Or not.

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The choice of greenhouse gas emissions scenario in recent study is intended to provide a plausible worst case scenario, but, as Bob points out, the projection of future risk, driven by the RCP 8.5 greenhouse gas scenario, is almost certainly too high, as advanced nations like the US have indeed bent the curve of emissions down to where it’s extremely unlikely that scenario would play out. They went with that choice though because it (somewhat) fit their description of plausible worst case scenario, but also apparently for convenience, because it was the only one that was included with the high frequency data needed in the CESM1-LENS dataset.

I don’t think the scientists picked the [model] “exhibiting the highest precipitation totals”, as Bob put it, rather it seems like they chose CESM1-LENS for its advanced features, like a relatively high resolution 1deg x 1deg cell size vs 2-3deg for the other global climate models, and this:

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Among the available global climate model large ensemble datasets, CESM1-LENS stands out with its comprehensive suite of three-dimensional, high-frequency (6 hourly) atmospheric variables, which provide the forcing conditions required for dynamical downscaling simulations.
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This enabled them to run a high resolution weather model driven by the larger scale global climate model in the mega-storm, to get a better idea of what the weather might actually be like during such an event.

Also CESM1-LENS has been validated against historic California precipitation, according to the study. So, it appears they had reasonable cause for basing the study on that model’s output.

Historically, the frequency of occurrence of these mega-storms appears to have been ~1/200 years. While the science is solid that a warming atmosphere contributes to more extreme rainfall events, the study’s estimate of 1/50 years for current risk should be taken with a sizable grain of salt. Maybe the real number is more like 1/100 or 1/150? No way to say for sure at the moment.

It’s something that will add a little extra ‘excitement’ to my observation of future medium to strong El Nino events, that’s for sure, as that seems to be when they happen.

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I get a little tired of government bashing in general, and California bashing specifically. So little of it is based in facts.

I’m always amazed and impressed when I drive on I-5 or 395 and see the massive pipes and aqueducts moving water around the state. Much of it 50 and 100+ years old. Surely we need to add to it to keep up with the population. But then, why have so many, over the many years kept moving here?

https://www.latimes.com/local/obituaries/archives/la-me-will…

Mike

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