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.
我们这周一直在关注美国路易斯安那州遭遇的历史性大洪水。现在通过数据来了解一下这场大洪水有多严重，路易斯安那州南部地区的灾情尤为严峻。
8月8日至14日，路易斯安那州全州的降水量累计达到6.9万亿加仑。利文斯顿县一天的降水量就超过31英寸。
洪水造成超过4万所房屋损坏，路易斯安那州州长称这是一场大灾难。截至目前，全州已有2万名居民获救。洪水已在全州造成11人死亡。
巴吞鲁日上次遭遇这种大灾难还要追溯至500年前。这意味着，这一灾难500年发生一次。
最后一个数据，路易斯安那州已有12个教区宣布成为联邦灾区。这加速了联邦政府的救援。其余教区也可能宣布成为联邦灾区。
此前我们介绍了暴洪的定义。现在詹妮弗·格雷将解释一下为什么这场洪水如此危险。

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.
cnn气象学家詹妮弗·格雷：从美国的情况来看，暴洪造成的死亡人数多于龙卷风、飓风和闪电。暴洪致使水流加速流动，可冲走成年男性和汽车，甚至还以冲走整座房屋。
地面饱和后，水就不能再渗入土壤中，因此积水会迅速流入河流和小溪，导致水位上涨，最终形成暴洪。
由于混凝土地面多、可将水吸收进土壤的绿地少，人口密集区发生暴洪的风险极高。暴洪会在人口密集区迅速形成。在山区，在积水注入河流、小溪甚至是流域以后，重力和径流的联合作用会引发灾难性洪水。
记住，暴洪可能会在眨眼之间发生。所以，保持警惕、留心你所在地区是否发出暴洪警报非常重要。