Tuesday, October 6, 2015

S. Carolina Flood: How It Happened, Climate Change, Warnings And Stupidity.

Water rescues near Columbia, South Carollina.
From WISTV.com  
The South Carolina flood that we've all been hearing about might be the nation's biggest disaster of 2015, and that's saying something.

After all, different parts of the country have endured intense droughts, huge wildfires, other major floods and storms. But South Carolina, where over two feet of rain fell in some areas, is in a class by itself.  

According to the Weather Channel, at least 11 deaths have been reported, there were at least 150 water rescues, 535 South Carolina roads and bridges are closed and 19 dams have been breached.

Larger rivers are still causing flood havoc in South Carolina this morning, even though the epic rains that caused the flooding have ended. This ain't over yet.

This was truly one of the most notorious, historic floods I've seen.

More water rescues in South Carolina. Photo by
Colin Duncan via WISTV.com  

Hurricane Joaquin was only a bit player in the meteorological drama that set up South Carolina's deadly flooding.

An area of low pressure, not a tropical storm, settled into the southeastern United States toward the end of last week, and then sat there.

This storm system drew in a big stream of super wet tropical air from the Atlantic Ocean.

One of the southeastern storm's tentacles reached all the way southeastward to Hurricane Joaquin, which was completely trashing many of the Bahama islands at the time.

The "atmospheric river" of moisture fed into an area of rising air that is fairly common to the northeast of the type of storm that was parked over the Southeast. This river was a string of thunderstorms that stayed in place for three days, repeatedly socking South Carolina with the torrential downpours.

This was made even worse by the fact that strong winds blew the storms and the moisture onshore, and overhead, upper level winds sort of fanned apart. This is known as a diffluence.

This meant there was air was being dispersed away from South Carolina far overhead. The atmosphere always seeks equilibrium, so air rose over the state to replace the upper level air being whisked away. Rising air leads to clouds and rain.

Inside a flooded South Carolina house. Photo by
Mike Buol via WISTV.com  
Since this diffluence in the upper atmosphere was strong, so were the updrafts. These strong updrafts further enhanced the rain.

The Washington Post's Capital Weather Gang has an awesome more detailed explanation of the meteorological factors that came together to cause this disaster.

The best part is you don't have to be a scientist to understand all this. Capital Weather Gang appeals to non-hard core geeks too.  

In addition, according to Capital Weather Gang, this South Carolina disaster might be an example of something called a predecessor rain event or PRE. (Further analysis is needed to make a firm assessment of this.)

PRE's are areas of heavy rain north of hurricanes that are distinct from these tropical storms but still indirectly tied to them, says Capital Weather Gang.

PRE's caused big flooding ahead of Hurricane Frances in 2004 around New York City and in the Midwest north of Tropical Storm Erin in 2007, for example.


Climate change was almost certainly not the sole cause of the South Carolina flood calamity, as noted above in the meteorological explanation of the storm.

However, but evidence suggests global warming contributed to this mess.

There have always been extreme rains and terrible flash floods, with or without global warming. The problem is, climate change makes such events more likely and more intense.
A business destroyed by the flood in Columbia,
South Carolina. Via WISTV.com  

Warmer air often holds more water vapor. More water vapor means more moisture is available for storms. When one gets going, the rain will be more intense than it otherwise would have been, had the atmosphere been cooler.

This means that some storms that might have in the past caused a so-so flood now causes a really nasty one.

We've seen a lot of unusually intense flash floods in recent years. This year alone, epic and deadly floods have hit places like Kentucky, Houston, Oklahoma City and Utah.

This weekend, while South Carolina was drowning, the French Riviera had its own catastrophic flood, which killed at least 19 people. 

According to the 2014 National Climate Assessment heavy precipitation events have increased by about 40 percent across the nation since 1900.

South Carolina Governor Nikki Haley described the flood as a 1,000 year event. Which is technically true. Given normal climate such a flood has a 0.1 percent chance of happening in any given year.

However, the United States has had no fewer than six 1,000 year flood events since 2010, according to USA Today. (This includes the epic Hurricane Irene flood that hit my home state of Vermont in 2011.) This is more evidence climate change is likely screwing around with precipitation.

Another culprit in the South Carolina disaster was unusually record or near record warm Atlantic Ocean waters off the East Coast.

As noted climate scientist Michael Mann tells Bradblog:

"Part of the story - and don't let anyone tell you otherwise - was record heat in the Atlantic, which means there was record moisture off the coast. And it's that record level of moisture in the atmosphere giving us these record levels of rainfall."

Ocean temperatures were also at record highs in the Bahamas as Hurricane Joachin trudged through the area. The high water temperatures were one reason why Joachin got a lot stronger than most meteorologists forecasted. (Another reason for Joachin's strength was unexpectedly favorable upper level winds.)
A flooded South Carolina business.  

A stronger Joachin might have loaded in more moisture for the fire hose of water directed at South Carolina over the weekend.

Less certain is whether the meteorlogical set up for the storm was related to climate change.

Does global warming increase the liklihood of stalled storms like the one over the Southeast this weekend? Does climate change mess around with jet stream dynamics, making storms like the one in South Carolina worse?

I'm sure scientists will be looking into it. I don't have a good answer at this point.


As always with floods, the South Carolina disaster brought out the heroics in some people, stupidity in others.

While most people headed South Carolina Emergency Management's plea for people who were in safe places to stay put, some ventured out.

One annoying thing I saw on social media is that businesses insisted on opening, despite the dangerous weather. That put their employees in danger as they felt forced to drive to work amid the high threat of flash flooding.

Hey, who cares if an employee or two dies as long as there's money to be made, right?

Even more appalling were the people who insisted on driving into clearly dangerous high water. Hey, I'll make it, I've got an SUV!!

Yeah, right pal.

I got a couple video examples as proof.

The guy in the first of the two videos you'll see below infuriates me. What was he thinking?  The water was clearly deep, flowing fast and getting worse. So he attempts to drive through it anyway.

This necessitated a good Samaritan to risk his life, rescuers to risk their lives to fish this guy out. And it's not as if first responders were twiddling their thumbs waiting for something to do. They were already responding to TONS of calls to rescue people from flooded homes, and other washed away cars.


The next guy made it through, too, but geez. He put a lot of people in danger, and less importantly, I'm sure his employer was thrilled that he almost destroyed the cargo in his tractor trailer:

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