S.C. flood is 6th 1,000-year rain since 2010

The biblical flooding in South Carolina is at least the sixth so-called 1-in-1,000 year rain event in the U.S. since 2010, a trend that may be linked to factors ranging from the natural, such as a strong El Niño, to the man-made, namely climate change.

So many "1-in-1,000 year" rainfalls is unprecedented, said meteorologist Steve Bowen of Aon Benfield, a global reinsurance firm. "We have certainly had our fair share in the United States in recent years, and any increasing trend in these type of rainfall events is highly concerning," Bowen said.

A "1-in-1,000 year event" means that there's a 1 in 1,000 (or 0.1% chance) of it happening in any given year in a given location, the National Oceanic and Atmospheric Administration (NOAA) said.

In addition to this weekend's floods in South Carolina, which killed at least nine people, the other 1-in-1,000-year rain events include the Tennessee floods in May 2010, the Mid-Atlantic, Northeast and New England drenching during Hurricane Irene in 2011, the Colorado floods in 2013, the deluge in Baltimore in August 2014, and the flooding earlier this year in Nebraska, according to Bowen.

South Carolina floods: Death toll rises to 9 in unrelenting storm

Scientists say there could be a connection between these floods and man-made climate change.

Research has confirmed that our warming climate is making intense short-term rains even heavier in many parts of the U.S. and the world, as warmer temperatures allow more moisture to evaporate from oceans and flow into rain-making storm systems, according to Weather Underground meteorologist Bob Henson.

A study earlier this year from Climate Central reported that 40 of the 48 contiguous states have recorded an uptick in heavy rain events in the past several decades (though South Carolina was not one of the 40).

The National Climate Assessment, a federal report from 2014, also found that a warming atmosphere would bring about more extreme rainfall events.

However, when speaking about this specific event, "I am very lukewarm on a climate change linkage," said University of Georgia meteorologist Marshall Shepherd in an e-mail. He said there is scientific evidence that the worst heavy rain events are increasing, "but I am not sure you can conclusively link this event."

Bowen added that huge floods occurred long before man-made climate change was an issue. "Atmospheric river events in particular have led to unbelievable rains throughout our recorded history, most notably the 1861-62 floods in California that flooded the Central Valley," he said.

Atmospheric rivers are ribbons of vapor that can extend thousands of miles from the tropics to the western U.S. and often provide the fuel for massive rainstorms in California. The 1861-62 floods were the worst in the recorded history of California.

Shepherd said storm-water management engineering may be behind the times, potentially exacerbating floods like that in South Carolina.

Given the vast size of the USA, it shouldn't be that surprising for extreme flooding to occur somewhere, Weather Underground meteorologist Bob Henson said in an e-mail. "Even very rare events do happen on a very limited basis when you're looking at a large area such as the United States," he said. "It's not hard to imagine getting 1-in-1000 year events at scattered locations over a few years' time."

It's also possible that the ongoing El Niño event, which has intensified throughout 2015, has played a role in boosting the amount of water vapor available for heavy rain across the southern U.S., Henson added.

El Niño is a natural climate pattern in which warmer-than-average Pacific Ocean temperatures change weather patterns around the world. Rain and snow from El Nino would help ease California's record drought.

Some parts of South Carolina received more rain in the past few days than some parts of California have seen in the past three years, according to AccuWeather.