CNN News:路易斯安那遭遇历史性洪水 已致11人死亡

One story we've been following this week is the historic flooding in the U.S. state of Louisiana. A by the numbers look helps us explain how bad it is, especially in Southern Louisiana.
Six-point-nine trillion, that's the number of gallons of rain that started all this, between August 8th and August 14th. Livingston Parish in particular got more than 31 inches of rain in just one day.
Forty thousand, that's the number of homes that had been damaged, in what Louisiana governor calls a major disaster. Twenty thousand, the number of people who've been rescued so far. Eleven deaths have been blamed on the floods across the state.
Five hundred years, the likelihood that a flood this catastrophic would occur in the Baton Rouge area. It means once every 500 years.
And finally, 12, the number of Louisiana parishes that had been declared federal disaster areas. That speeds up federal government assistance to them. More than 12 other parishes may also get this declaration.
We touched on the definition of flash floods the other day. Jennifer Gray now explores what makes this flood so dangerous.

JENNIFER GRAY, cnn METEOROLOGIST: In the U.S., flash floods kill more people than tornadoes, hurricanes or lighting. A flash flood creates a rush of moving water than can sweep a grown man off his feet, a car off the road and even your entire home off its foundation.
When the ground becomes so saturated that water can no longer seep in to the soil, it begins to run off quickly into rivers and streams and this causes a rise in water and a flash.
Densely populated areas have an extremely high risk of flash flooding with additional concrete than less grassy areas for the water to soak into the soil. And they can see flash flooding very quickly. In mountainous terrain, the combination of gravity, plus the easy runoff can lead to catastrophic flooding when all of that water is funneled into rivers, creeks and even the valleys.
Remember, flash flooding can happen in the blink of an eye. That's why it's important to stay alert and pay attention in case a flash flood watch or warning is issued for your area.