Re: The coming megafloods -- Scientific American

Megastorms Could Drown Massive Portions of California
Huge flows of vapor in the atmosphere, dubbed "atmospheric rivers," have unleashed massive floods every 200 years, and climate change could bring more of them

By Michael D. Dettinger and B. Lynn Ingram | Friday, November 30, 2012

Editor's note (11/30/12): The article will appear in the January 2013 issue of Scientific American. We are making it freely available now because of the flooding underway in California.

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. Thousands of people died, and one quarter of the state’s estimated 800,000 cattle drowned. 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.


http://www.scientificamerican.com/article.cfm?id=megastorms-could-down-massive-portions-of-california&print=true&utm_source=buffer&buffer_share=9f463



Edited 1 time(s). Last edit at 11/30/2012 09:13PM by KenS.

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KenS
Megastorms Could Drown Massive Portions of California
Huge flows of vapor in the atmosphere, dubbed "atmospheric rivers," have unleashed massive floods every 200 years, and climate change could bring more of them

By Michael D. Dettinger and B. Lynn Ingram | Friday, November 30, 2012

Editor's note (11/30/12): The article will appear in the January 2013 issue of Scientific American. We are making it freely available now because of the flooding underway in California.

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.

Sigh...

That first sentence is such a weasel sentence... Yes, the current climate warming could bring more of them, but it could theoretically decrease the frequency of them. No one really knows.

Just a point of reference though. That last mega-flood that occurred in the winter of 1861-1862 occurred at the end of the Little Ice Age. And many of the mega-floods before that one occurred during the Little Ice Age. So it's really a stretch to say that the current global warming will result in more frequent mega-floods. There's no historical evidence to back up that assertion.

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plawrence
Just a point of reference though. That last mega-flood that occurred in the winter of 1861-1862 occurred at the end of the Little Ice Age. And many of the mega-floods before that one occurred during the Little Ice Age. So it's really a stretch to say that the current global warming will result in more frequent mega-floods. There's no historical evidence to back up that assertion.
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You are right, in the sense that those mega-floods probably included a lot of warm-rain-induced snow melt. That was certainly a big factor in the much smaller (but still very damaging) great flood that started right after Christmas in 1996. The river valleys in Yosemite won't recover from that one for a long time. But the glacier levels in the high sierra are much reduced from what they were a hundred and fifty years ago. The snow pack is probably less, too. So there may be a little less fuel for the fire now, so to speak.

Anyway, one good point to take from that article is not about the frequency of such mega-floods, but rather that they are absolutely quite possible today. Like the great earthquakes, they will surely happen again. We have spent a lot of resources trying to shore up our buildings against the great quake, but almost nothing against the great flood. The big cities in CA are terribly vulnerable. Don't build your house upon the sand, and all that...

Me, I built my house in San Jose on a solid rock hill 400 feet above sea level. It didn't notice the Loma Prieta quake, whose epicenter was only a few miles away (though about half the water sloshed out of my swimming pool) and it won't notice the great flood either. Until the water, sewer, and electric services all shut down for months, and the highway bridges are all gone. And all the California crops are gone, too. I could move back to North Dakota, but they have been having drought there. I could move to the coast, but they have tsunamis. Fortunately, my actuarial life expectancy is pretty short now. I'll most like die before the big disaster hits. But you whippersnappers might think about moving somewhere else, and reducing the traffic jams between here and Yosemite.

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wherever

We have spent a lot of resources trying to shore up our buildings against the great quake, but almost nothing against the great flood.

Actually, that's not true. All those dams that were built in the Sierra weren't built just to quench the thirst of a growing state and irrigate its crops and provide power. Most of them were built also to help reduce the risk of a great flood causing widespread damage.

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actually north dakota got some major floods in a variety of areas throughout the state in 2011. i worked in doing some pretty major flood restoration work in the national parks and historic sites when the floods occurred in ND during 2011. one life lesson i learned is if you are going to build a house, try and build it on top of a hill if possible where it can't get flooded



Edited 3 time(s). Last edit at 12/02/2012 12:21AM by marmot.